Are you guys still gonna run 20/50 weight oil in the Winter?
11-01-01, 09:33 AM
#26
Original Gangster/Rotary!
iTrader: (213)
Originally posted by kwikrx7
10W-30 or 20W-50 are fine. I use 20W-50 beacuse of the heat issue but I also have oil-porting done and also the eccentric-shaft plug mod done.....I have heard not to switch back and forth and just to stay with one so you might not spin a bearing.
10W-30 or 20W-50 are fine. I use 20W-50 beacuse of the heat issue but I also have oil-porting done and also the eccentric-shaft plug mod done.....I have heard not to switch back and forth and just to stay with one so you might not spin a bearing.
so you're saying you run 20w50 year round, even in the PA winters?
11-01-01, 08:22 PM
#28
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Why would you want to start your RX7 in 20 deg weather with 20w50 molasses oil? Twice as hard to pump when cold? Not in my RX7. Every manufacturer recommends dropping viscosity under winter conditions.
Again, you want the oil to flow in a rotary since it is used to cool the engine. The faster you get hot oil moving away to be cooled the better. What other car with a 1.3 liter engine has a oil cooler?
I think the comments about the pre-cat and the cooling are not relevant to this discussion. Everyone knows that the EPA required the pre-cat. The underhood head from this is probably one of the reasons the car is no longer imported (does anyone remember all the FD fires prior to the hose recalls?). Cooling was designed for a 255hp car with a new radiator. Higher hp and mileage probably make the radiator marginal (although I have no problems). Remember the car was designed as light as possible so some of the systems are not as over-engineered as other cars.
How can you bust on the FD? Even after all these years, it is one if not the best handling car hands down. It wone the Turbo Mag and Sports Compact Car shootout against 2 Supra's. If you want an appreciation of the work which went into the car, I highly recommend 'RX-7 Mazda's Legendary Sports Car' by Jack Yamaguchi and John Dinkel. The whole book details the development of the 3rd gen RX7. You see a discussion of every major car system, including oil and cooling.
Unless you car is running higher oil pressure, and is ported and clearenced, I would stick to Mazda's recommendations, especially in a cold climate.
But I'm willing to listen to a compelling argument. Convince me you are not doing damage to the engine using 20w50 in the winter.
Again, you want the oil to flow in a rotary since it is used to cool the engine. The faster you get hot oil moving away to be cooled the better. What other car with a 1.3 liter engine has a oil cooler?
I think the comments about the pre-cat and the cooling are not relevant to this discussion. Everyone knows that the EPA required the pre-cat. The underhood head from this is probably one of the reasons the car is no longer imported (does anyone remember all the FD fires prior to the hose recalls?). Cooling was designed for a 255hp car with a new radiator. Higher hp and mileage probably make the radiator marginal (although I have no problems). Remember the car was designed as light as possible so some of the systems are not as over-engineered as other cars.
How can you bust on the FD? Even after all these years, it is one if not the best handling car hands down. It wone the Turbo Mag and Sports Compact Car shootout against 2 Supra's. If you want an appreciation of the work which went into the car, I highly recommend 'RX-7 Mazda's Legendary Sports Car' by Jack Yamaguchi and John Dinkel. The whole book details the development of the 3rd gen RX7. You see a discussion of every major car system, including oil and cooling.
Unless you car is running higher oil pressure, and is ported and clearenced, I would stick to Mazda's recommendations, especially in a cold climate.
But I'm willing to listen to a compelling argument. Convince me you are not doing damage to the engine using 20w50 in the winter.
11-02-01, 01:45 AM
#29
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Okay, why not run Castrol GTX 10/40 then and have the best of both worlds?
Also, msdbman,
============================
But I'm willing to listen to a compelling argument. Convince me you are not doing damage to the engine using 20w50 in the winter.
============================
Answer: doesn't it depend on where you live? Here in Southern California, it doesn't as cold as places like Washington or Montana?
Also, msdbman,
============================
But I'm willing to listen to a compelling argument. Convince me you are not doing damage to the engine using 20w50 in the winter.
============================
Answer: doesn't it depend on where you live? Here in Southern California, it doesn't as cold as places like Washington or Montana?
Last edited by frank69m; 11-02-01 at 01:48 AM.
11-02-01, 07:07 AM
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Yes, geography does play a part. I think I already discussed this in one of my first posts about what the Tuners recommend.
Even so, I'm still not convinced you want thick molasses oil in a rotary. Anyone know why the tuners recommend this? Is low viscosity an issue under race conditions? Just the facts, Maam...
Even so, I'm still not convinced you want thick molasses oil in a rotary. Anyone know why the tuners recommend this? Is low viscosity an issue under race conditions? Just the facts, Maam...
11-02-01, 09:10 AM
#31
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oil
The comments on oil viscosity, thermal breakdown, etc. are interesting. I'm old enough to remember non-detergent oil. Any of you guys ever use it? A lot of the comments here are theoretical issues that the major oil companies have been working on for 50 years. Their improvements in the use of oil additives and the development of synthetics are the result of the combined expertise of groups of people who spend their entire careers on this subject. My point is- unless you are buying some **** brand of oil that has been sitting on a shelf in Podunk, Arkansas since 1943, there have been industry standards implemented that ALL oil has to meet for passenger cars (racing is a different issue). Check the label- it will state "meets xxx ,xxx, xxx, etc. standards". If your FD is getting hot enough to boil, thermal break, or otherwise destroy the film strength of the oil, you have other problems not related to the oil. Changing the oil frequently is the only commonly held opinion. While many of us mock some of the design features that Mazda built into the RX-7, their engineers know a lot more about the internal engine design and its lubrication requirements than most of us. My $0.02. (10W-30). My apologies to the residents of Podunk, AR. No disrespect was intended.
Last edited by ronarndt; 11-02-01 at 09:16 AM.
11-02-01, 09:17 AM
#32
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sure, the oil "looks like molasses" when you pour it out of the bottle at 30 degree ambient temps, but how long is the engine (and the oil) at that temp after the spark plugs fire? NOT VERY LONG....like a few seconds....these engines warm up damn quick....and I don't think ANY oil is going to prevent all cold start wear, although synthetics are very good
my point is, after a few minutes of warm-up, the other hour or two you operate the car, even a 20w-50 is flowing extremely well, you'd be very surprised
also, at very cold temps, the metal surfaces inside the engine contract and the surfaces do not wear as much as they do when warm
the ONLY valid argument against the heavier oil is formation of deposits....and I don't care about that becasue this is a rotary and I put nasty 2-stroke oil in the gas, anyway
my point is, after a few minutes of warm-up, the other hour or two you operate the car, even a 20w-50 is flowing extremely well, you'd be very surprised
also, at very cold temps, the metal surfaces inside the engine contract and the surfaces do not wear as much as they do when warm
the ONLY valid argument against the heavier oil is formation of deposits....and I don't care about that becasue this is a rotary and I put nasty 2-stroke oil in the gas, anyway
11-02-01, 04:20 PM
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Ok, here's a long post from Castrol's web site: http://www.castrolusa.com/expert/default.asp
In short, the info below seems to point to 10w30 in cooler climates, but to 20w50 for hotter climates, high rpm race engines.
I went to http://www.castrolusa.com/gradeCalculator.asp and got the following:
According to the information you have provided, The Expert recommends following your manufacturer’s guidelines for a 1993 MAZDA RX-7. Castrol grades which correspond to these guidelines are as follows: Castrol GTX SAE 10W-30, Castrol Syntec SAE 10W-30, Castrol Syntec Blend SAE 10W-30.
If you often drive under extreme conditions (frequent short trips, driving in stop and go traffic, towing and hauling, extreme temperatures) or you simply want some additional peace of mind, you may wish to consider selecting this grade in a Full Synthetic motor oil such as Castrol Syntec for the ultimate in engine protection, or a part synthetic motor oil such Syntec Blend for added engine protection.
Note: If you live in a warm climate, you may want to consider using a heavier weight oil, such as a 20w50. If you live in a primarily cold climate, you might prefer a lighter weight oil, such as 5w30 to facilitate oil flow at startup. For more information about oil grade please see the Expert’s All About Oil information <http://www.castrolusa.com/expert/aeA...p?section_id=3>.
Changing your car's oil every 3 months or 3 thousand miles is the most important thing you can do to extend the life of your car. To help keep you on track, Castrol's Expert will email you when it is time to change your oil. To sign up for this free service, CLICK HERE <javascript:updateParent('http://www.castrolusa.com/about/signup.asp'); close();>. However, this tool is just a guide and is to be used only for reference. Castrol disclaims any and all liabilities arising from or relating to the use of this tool. Before changing your oil, please consult your car's instructional manual or a professional lube center.
Motor Oil: the Basics
OK, we've established that it's important for you to change your oil religiously. It's vital for your car's engine to have clean, fresh oil to properly do its job. But you still may be wondering what motor oil is exactly and how it works.
Well, let's start with the basics. The oil used in your car has two primary ingredients: base oil and additives. The base oil allows the motor oil to perform its vital function - lubricating the engine's moving parts to protect them against wear and tear caused by friction. The additives provide additional engine protection by helping prevent the oil from deteriorating under the extreme temperature conditions in the engine.
The base oil is refined from crude (oil in its natural state when pumped from the ground). The crude must undergo a variety of refining processes before yielding base stock suitable for use in engine oil. Undesirable components such as wax, sulfur and nitrogen compounds must be removed. Unsaturated hydrocarbons must be extracted or converted into more stable molecules. Crude is first separated by vacuum distillation into a series of fractions or viscosity ranges. The fractions intended for base oil production are processed further using various combinations of refining processes, such as:
Solvent Extraction- separates the naturally occurring saturated and unsaturated hydrocarbons.
Hydrofinishing- removes some of the nitrogen and sulfur compounds, improves color, oxidation and thermal stability of base stock.
Hydrotreating- converts some of the unsaturated hydrocarbons to saturated hydrocarbons to help improve yield prior to solvent extraction. This process also helps remove of large portion of sulfur and some nitrogen compounds.
Hydrocracking- a sophisticated process in which molecules in the base stock fraction are rearranged into the desirable saturated hydrocarbon molecules. The yield of saturated molecules is much greater than that achieved with hydrotreating and solvent extraction.
Hydroisomerization- when used along with hydrocracking, can transform the molecules of the base stock fraction into the most stable form possible.
Base oil alone is not enough to properly protect your engine. A motor oil needs to perform a wide variety of functions under a wide range of engine operating conditions. Therefore several additives are incorporated into the formulation:
Detergent/dispersant additives- are used to maintain engine cleanliness, keeping the various contaminants in a fine suspension and preventing them from settling out on vital engine components.
Rust and corrosion inhibitors- are added to protect the engine from water and acids formed as combustion by-products.
Antioxidants- are added to inhibit the oxidation process, which can result in oil thickening and sludge formation.
Anti-wear additives- form a film on metal surfaces to help prevent metal-to-metal contact.
Viscosity modifiers and pour point depressants- help improve the flow characteristics of motor oil.
Now that you know what motor oil is, how it is made and what it does, here comes the most confusing part of all: grades. In order for motor oil to perform its major function - lubrication - its viscosity (the measure of it's thickness or resistance to flow) must be capable of holding up under your engine's extreme temperature conditions. Oil thins when heated and thickens when cooled. Choosing the proper viscosity grade for the ambient temperature of your geographic location becomes vitally important.
A monograde is an oil whose viscosity is defined at only one temperature, either high or low. A multigrade must meet both high and low temperature viscosity requirements simultaneously. This makes multigrades an easy and popular year-round choice for drivers who experience hot summers and harsh winters. They are easily recognized by the dual viscosity designation (i.e. 10W-30 where the 10W is the low temperature, or winter designation and the 30 is the high temperature designation). It is the viscosity modifier additive that produces a thickening effect at high temperatures but is dormant at low temperatures.
Information concerning the performance, viscosity grade and energy conserving properties of an oil can be found within the API Service Symbol, also known as the "Donut". This symbol displays the API (American Petroleum Institute) Service rating, a two-letter classification that identifies the quality level of the motor oil and the type of vehicle it is suited for. The first letter "S" indicates the oil is appropriate for "spark ignition" or gasoline engines. The first letter "C" indicates the oil is intended for "compression ignition" or diesel engines. The second letter in each category indicates the performance level of category. For the "S" categories, the performance level increases as the categories go through the alphabet. However, the same is not true for the "C" categories as the types and intended application range for diesel vehicles vary greatly. It is important to refer to the owners' manual for appropriate performance recommendation.
In the center of the donut will be the SAE (Society of Automotive Engineers) viscosity classification. The bottom of the donut is reserved to convey the energy conserving properties of the oil as determined in a standard industry test.
If an oil meets both the latest "S" API service category and the current energy conserving standard, it is also able to display the API Certification Symbol, known as the "Starburst". The Starburst will always be found on the front label.
SAE Viscosity Grade Temperature Conditions Descriptions
5W-30 Below 0° F Provides excellent fuel economy and low-temperature performance in most late-model automobiles. Especially recommended for new cars.
10W-30 Above 0° F Most frequently recommended viscosity grade for most automobile engines, including high-performance multivalve engines and turbo-charged engines.
10W-40 Above 0° F The first multigrade introduced. A good choice for controlling engine wear and preventing oil breakdown from oxidation. Note: Always check your owner's manual or warranty requirements before using this grade.
20W-50 Above 20° F Provides maximum protection for high-performance, high-RPM racing engines. Excellent choice for high temperature and heavy loads such as driving in the desert or towing a trailer at high speeds for long periods of time.
SAE 30
SAE 40 Above 40° F
Above 60° F For cars and light trucks, where recommended by manufacturers. Not recommended when cold-temperature starting is required.
Category Status Service
SJ Current For all automotive engines presently in use. Introduced in the API service symbol in 1996
SH Obsolete For model year 1996 and older engines. Precede by certain C categories
SG Obsolete For model year 1993 and older engines
SF Obsolete For 1988 and older engines
SE Obsolete For 1979 and older engines
SD Obsolete For 1971 and older engines
SC Obsolete For 1967 and older engines
SB Obsolete For older engines. Use only when recommended by the manufacturer.
SA Obsolete For older engines; no performance requirement. Use only when recommended by the manufacturer.
In short, the info below seems to point to 10w30 in cooler climates, but to 20w50 for hotter climates, high rpm race engines.
I went to http://www.castrolusa.com/gradeCalculator.asp and got the following:
According to the information you have provided, The Expert recommends following your manufacturer’s guidelines for a 1993 MAZDA RX-7. Castrol grades which correspond to these guidelines are as follows: Castrol GTX SAE 10W-30, Castrol Syntec SAE 10W-30, Castrol Syntec Blend SAE 10W-30.
If you often drive under extreme conditions (frequent short trips, driving in stop and go traffic, towing and hauling, extreme temperatures) or you simply want some additional peace of mind, you may wish to consider selecting this grade in a Full Synthetic motor oil such as Castrol Syntec for the ultimate in engine protection, or a part synthetic motor oil such Syntec Blend for added engine protection.
Note: If you live in a warm climate, you may want to consider using a heavier weight oil, such as a 20w50. If you live in a primarily cold climate, you might prefer a lighter weight oil, such as 5w30 to facilitate oil flow at startup. For more information about oil grade please see the Expert’s All About Oil information <http://www.castrolusa.com/expert/aeA...p?section_id=3>.
Changing your car's oil every 3 months or 3 thousand miles is the most important thing you can do to extend the life of your car. To help keep you on track, Castrol's Expert will email you when it is time to change your oil. To sign up for this free service, CLICK HERE <javascript:updateParent('http://www.castrolusa.com/about/signup.asp'); close();>. However, this tool is just a guide and is to be used only for reference. Castrol disclaims any and all liabilities arising from or relating to the use of this tool. Before changing your oil, please consult your car's instructional manual or a professional lube center.
Motor Oil: the Basics
OK, we've established that it's important for you to change your oil religiously. It's vital for your car's engine to have clean, fresh oil to properly do its job. But you still may be wondering what motor oil is exactly and how it works.
Well, let's start with the basics. The oil used in your car has two primary ingredients: base oil and additives. The base oil allows the motor oil to perform its vital function - lubricating the engine's moving parts to protect them against wear and tear caused by friction. The additives provide additional engine protection by helping prevent the oil from deteriorating under the extreme temperature conditions in the engine.
The base oil is refined from crude (oil in its natural state when pumped from the ground). The crude must undergo a variety of refining processes before yielding base stock suitable for use in engine oil. Undesirable components such as wax, sulfur and nitrogen compounds must be removed. Unsaturated hydrocarbons must be extracted or converted into more stable molecules. Crude is first separated by vacuum distillation into a series of fractions or viscosity ranges. The fractions intended for base oil production are processed further using various combinations of refining processes, such as:
Solvent Extraction- separates the naturally occurring saturated and unsaturated hydrocarbons.
Hydrofinishing- removes some of the nitrogen and sulfur compounds, improves color, oxidation and thermal stability of base stock.
Hydrotreating- converts some of the unsaturated hydrocarbons to saturated hydrocarbons to help improve yield prior to solvent extraction. This process also helps remove of large portion of sulfur and some nitrogen compounds.
Hydrocracking- a sophisticated process in which molecules in the base stock fraction are rearranged into the desirable saturated hydrocarbon molecules. The yield of saturated molecules is much greater than that achieved with hydrotreating and solvent extraction.
Hydroisomerization- when used along with hydrocracking, can transform the molecules of the base stock fraction into the most stable form possible.
Base oil alone is not enough to properly protect your engine. A motor oil needs to perform a wide variety of functions under a wide range of engine operating conditions. Therefore several additives are incorporated into the formulation:
Detergent/dispersant additives- are used to maintain engine cleanliness, keeping the various contaminants in a fine suspension and preventing them from settling out on vital engine components.
Rust and corrosion inhibitors- are added to protect the engine from water and acids formed as combustion by-products.
Antioxidants- are added to inhibit the oxidation process, which can result in oil thickening and sludge formation.
Anti-wear additives- form a film on metal surfaces to help prevent metal-to-metal contact.
Viscosity modifiers and pour point depressants- help improve the flow characteristics of motor oil.
Now that you know what motor oil is, how it is made and what it does, here comes the most confusing part of all: grades. In order for motor oil to perform its major function - lubrication - its viscosity (the measure of it's thickness or resistance to flow) must be capable of holding up under your engine's extreme temperature conditions. Oil thins when heated and thickens when cooled. Choosing the proper viscosity grade for the ambient temperature of your geographic location becomes vitally important.
A monograde is an oil whose viscosity is defined at only one temperature, either high or low. A multigrade must meet both high and low temperature viscosity requirements simultaneously. This makes multigrades an easy and popular year-round choice for drivers who experience hot summers and harsh winters. They are easily recognized by the dual viscosity designation (i.e. 10W-30 where the 10W is the low temperature, or winter designation and the 30 is the high temperature designation). It is the viscosity modifier additive that produces a thickening effect at high temperatures but is dormant at low temperatures.
Information concerning the performance, viscosity grade and energy conserving properties of an oil can be found within the API Service Symbol, also known as the "Donut". This symbol displays the API (American Petroleum Institute) Service rating, a two-letter classification that identifies the quality level of the motor oil and the type of vehicle it is suited for. The first letter "S" indicates the oil is appropriate for "spark ignition" or gasoline engines. The first letter "C" indicates the oil is intended for "compression ignition" or diesel engines. The second letter in each category indicates the performance level of category. For the "S" categories, the performance level increases as the categories go through the alphabet. However, the same is not true for the "C" categories as the types and intended application range for diesel vehicles vary greatly. It is important to refer to the owners' manual for appropriate performance recommendation.
In the center of the donut will be the SAE (Society of Automotive Engineers) viscosity classification. The bottom of the donut is reserved to convey the energy conserving properties of the oil as determined in a standard industry test.
If an oil meets both the latest "S" API service category and the current energy conserving standard, it is also able to display the API Certification Symbol, known as the "Starburst". The Starburst will always be found on the front label.
SAE Viscosity Grade Temperature Conditions Descriptions
5W-30 Below 0° F Provides excellent fuel economy and low-temperature performance in most late-model automobiles. Especially recommended for new cars.
10W-30 Above 0° F Most frequently recommended viscosity grade for most automobile engines, including high-performance multivalve engines and turbo-charged engines.
10W-40 Above 0° F The first multigrade introduced. A good choice for controlling engine wear and preventing oil breakdown from oxidation. Note: Always check your owner's manual or warranty requirements before using this grade.
20W-50 Above 20° F Provides maximum protection for high-performance, high-RPM racing engines. Excellent choice for high temperature and heavy loads such as driving in the desert or towing a trailer at high speeds for long periods of time.
SAE 30
SAE 40 Above 40° F
Above 60° F For cars and light trucks, where recommended by manufacturers. Not recommended when cold-temperature starting is required.
Category Status Service
SJ Current For all automotive engines presently in use. Introduced in the API service symbol in 1996
SH Obsolete For model year 1996 and older engines. Precede by certain C categories
SG Obsolete For model year 1993 and older engines
SF Obsolete For 1988 and older engines
SE Obsolete For 1979 and older engines
SD Obsolete For 1971 and older engines
SC Obsolete For 1967 and older engines
SB Obsolete For older engines. Use only when recommended by the manufacturer.
SA Obsolete For older engines; no performance requirement. Use only when recommended by the manufacturer.
11-02-01, 04:43 PM
#34
Passenger
Posts: n/a
I guess that is alot of nice facts and figures there, but it doesn't really mean a whole lot...it's just spit out by a computer for a generic application by people that don't really much abou tthe specific needs of rotaries or turbo cars...so it's the Castrol website...who cares? I'll take the word of a racer who tears down engines over that any day...namely Cam Worth of Pettit
TURBOS ARE EXTREMELY HARD ON OIL....IMAGINE PUTTING YOUR OIL IN A EGG BEATER AND CRANKING IT UP TO 10,000 RPM FOR A FEW MINUTES...CAN YOU DIG IT? THAT TENDS TO CHOP THE HELL OUT OF THE MOLECULES AND ADDITIVES REAL DAMN QUICK
I'll keep using my 20W-50....keep using your 10W-30...my engine will outlast yours
TURBOS ARE EXTREMELY HARD ON OIL....IMAGINE PUTTING YOUR OIL IN A EGG BEATER AND CRANKING IT UP TO 10,000 RPM FOR A FEW MINUTES...CAN YOU DIG IT? THAT TENDS TO CHOP THE HELL OUT OF THE MOLECULES AND ADDITIVES REAL DAMN QUICK
I'll keep using my 20W-50....keep using your 10W-30...my engine will outlast yours
11-02-01, 04:58 PM
#35
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I guess you did not read my post very carefully. The text tends to agree with you regarding high rpm, racing engines and warm climates 20w50. I think we are both more likely to ping the engine and blow it rather than wear it out from oil breakdown. If were were taking about a 1G or 2G non-turbo then we would have a good experiment.
I respect Cam's opinion and they are correct for the FL climate and a car you run hard. I've visited his facility last summer - I have much more respect for his shop than PFS(which I've also visited).
On the other hand, I can respect all the Mazda engineers who spent years designing the 13B's lubrication and cooling system and their recommendations.
My answer would be in cold climate here in DE: 10w30 winter, 20w50 summer (if you run the car hard).
We haven't touched on the Synthetic vs conventional issue hotly debated. I just came off the Mobile1 site - here's more fuel to the fire: http://www.mobil1.com/why/myths.jsp
Mobil 1 can't be used in Mazda rotary engines.
While Mazda doesn't recommend synthetic oils in general for its rotary engines, experience and testing have shown that Mobil 1 provides superior performance in rotary engines. Check with your Mazda representative concerning warranty questions.
Using Mobil 1 will void my new-car warranty.
Mobil 1 exceeds the American Petroleum Institute (API) engine oil service requirements of all new-car manufacturers, both domestic and foreign. Mobil 1 is the factory-fill oil in Chevrolet Corvette, Dodge Viper, all Porsches, Mercedes-Benz AMG and all Aston Martin automobiles. The rotary-engined Mazda RX-7 is the only vehicle whose manufacturer does not recommend the use of any synthetic oil.
I respect Cam's opinion and they are correct for the FL climate and a car you run hard. I've visited his facility last summer - I have much more respect for his shop than PFS(which I've also visited).
On the other hand, I can respect all the Mazda engineers who spent years designing the 13B's lubrication and cooling system and their recommendations.
My answer would be in cold climate here in DE: 10w30 winter, 20w50 summer (if you run the car hard).
We haven't touched on the Synthetic vs conventional issue hotly debated. I just came off the Mobile1 site - here's more fuel to the fire: http://www.mobil1.com/why/myths.jsp
Mobil 1 can't be used in Mazda rotary engines.
While Mazda doesn't recommend synthetic oils in general for its rotary engines, experience and testing have shown that Mobil 1 provides superior performance in rotary engines. Check with your Mazda representative concerning warranty questions.
Using Mobil 1 will void my new-car warranty.
Mobil 1 exceeds the American Petroleum Institute (API) engine oil service requirements of all new-car manufacturers, both domestic and foreign. Mobil 1 is the factory-fill oil in Chevrolet Corvette, Dodge Viper, all Porsches, Mercedes-Benz AMG and all Aston Martin automobiles. The rotary-engined Mazda RX-7 is the only vehicle whose manufacturer does not recommend the use of any synthetic oil.
11-02-01, 05:24 PM
#36
Passenger
Posts: n/a
I'm a firm believer in synthetics and I know Pettit runs their race cars with synthetic and has not expereinced any problems, but they also run the "Protek R" premix in the gas for apex seal lubrication (apparently)....I think the jury is still out on this issue, but I tend to think synthetics are safe, if you run pre-mix
if I ran a synthetic in a rotary, here is what I would pick
http://www.amsoil.com/products/tro.html
if I ran a synthetic in a rotary, here is what I would pick
http://www.amsoil.com/products/tro.html
11-02-01, 06:54 PM
#37
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Remember,
Synthetics have a higher ash content which results in increased deposits in the engine. For example, Castrol Syntec has 50% more ash content versus Castrol GTX. When injecting it into the engine, this will result in a higher chance of deposits, which can cause engine failure. Now if you use premix in the gas tank instead of oil injection, synthetic is the best way to go. The synthetic is the best oil for the turbos and does not coke up as quickly. It has a higher flash point, so it is a more stable oil at higher temperatures. Turbo applications would be greatly benefited by synthetic oils.
Synthetics void new car warranties because the oil is too slippery. This does not allow the engine components to properly seat. For example, if you rebuild a piston engine and start with synthetic from the start, the rings will not have a chance to seat properly, thus causing the engine to fail. (my friend had this happen to a racing engine). Once the engine has been through a proper break-in period (5k to 10K miles), it is OK to use synthetic oils.
One more comment: If the "TURBOS ARE EXTREMELY HARD ON OIL...TENDS TO CHOP THE HELL OUT OF THE MOLECULES AND ADDITIVES REAL DAMN QUICK", Then why would anyone use multigrade oils in turbo cars? The molecules in 10W30 and 20W50 are both going to be chopped up equally. If anything, the viscosity modifiers would be sheared quicker in a thicker oil as the shear viscosity is higher. To get better consistent protection, don't you think using SAE 30 straight weight with no viscosity modifiers would be even better? Once the viscosity modifiers are broken down, you only end up with SAE20 equivalent oil (assuming that all the viscosity modifiers are chopped up quickly)? I point this out only to explain that viscosity modifiers break down at a rate that WE DO NOT KNOW since we are not oil experts. If anyone has test results for this type of action, please post as we need this information to make an educated determination of the correct oil to use. Also, there are other factors like blow-by gasses that can change the oil's viscosity quickly.
Tim
Synthetics have a higher ash content which results in increased deposits in the engine. For example, Castrol Syntec has 50% more ash content versus Castrol GTX. When injecting it into the engine, this will result in a higher chance of deposits, which can cause engine failure. Now if you use premix in the gas tank instead of oil injection, synthetic is the best way to go. The synthetic is the best oil for the turbos and does not coke up as quickly. It has a higher flash point, so it is a more stable oil at higher temperatures. Turbo applications would be greatly benefited by synthetic oils.
Synthetics void new car warranties because the oil is too slippery. This does not allow the engine components to properly seat. For example, if you rebuild a piston engine and start with synthetic from the start, the rings will not have a chance to seat properly, thus causing the engine to fail. (my friend had this happen to a racing engine). Once the engine has been through a proper break-in period (5k to 10K miles), it is OK to use synthetic oils.
One more comment: If the "TURBOS ARE EXTREMELY HARD ON OIL...TENDS TO CHOP THE HELL OUT OF THE MOLECULES AND ADDITIVES REAL DAMN QUICK", Then why would anyone use multigrade oils in turbo cars? The molecules in 10W30 and 20W50 are both going to be chopped up equally. If anything, the viscosity modifiers would be sheared quicker in a thicker oil as the shear viscosity is higher. To get better consistent protection, don't you think using SAE 30 straight weight with no viscosity modifiers would be even better? Once the viscosity modifiers are broken down, you only end up with SAE20 equivalent oil (assuming that all the viscosity modifiers are chopped up quickly)? I point this out only to explain that viscosity modifiers break down at a rate that WE DO NOT KNOW since we are not oil experts. If anyone has test results for this type of action, please post as we need this information to make an educated determination of the correct oil to use. Also, there are other factors like blow-by gasses that can change the oil's viscosity quickly.
Tim
11-02-01, 10:14 PM
#38
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Tim,
good post, but I would like to see the source(s) of some of your claims, and I've been doing some research myself
1) "if anything, the viscosity modifiers would be sheared quicker in a thicker oil as the shear viscosity is higher"
maybe the "shear viscosity" is higher, but the viscosity STABILITY of 20w-50 is superior
http://www.redlineoil.com/frames/whyoil.htm
also, look at the specification for high temperature/shear at the bottom of this page for Amsoil 20w/50 synthetic
http://www.amsoil.com/products/tro.html
then look at this one for 0w-30
http://www.amsoil.com/products/tso.html
2) "synthetics have a high ash content"
what is your basis for this statement?
read this excellent Amsoil article, 7th paragraph down
http://www.guarding-our-earth.com/de...reakdown.shtml
it contradicts your statement
after reading this stuff, I'm going full synthetic!! either 20w-50 or 15w-50
ideally, I need to get my hands on some ASME papers from my brother (who works for GM Advanced Vehicle Engineering) that deal with this topic in detail, because research prepared by vendors is obviously biased, to one extent or the other
good post, but I would like to see the source(s) of some of your claims, and I've been doing some research myself
1) "if anything, the viscosity modifiers would be sheared quicker in a thicker oil as the shear viscosity is higher"
maybe the "shear viscosity" is higher, but the viscosity STABILITY of 20w-50 is superior
http://www.redlineoil.com/frames/whyoil.htm
also, look at the specification for high temperature/shear at the bottom of this page for Amsoil 20w/50 synthetic
http://www.amsoil.com/products/tro.html
then look at this one for 0w-30
http://www.amsoil.com/products/tso.html
2) "synthetics have a high ash content"
what is your basis for this statement?
read this excellent Amsoil article, 7th paragraph down
http://www.guarding-our-earth.com/de...reakdown.shtml
it contradicts your statement
after reading this stuff, I'm going full synthetic!! either 20w-50 or 15w-50
ideally, I need to get my hands on some ASME papers from my brother (who works for GM Advanced Vehicle Engineering) that deal with this topic in detail, because research prepared by vendors is obviously biased, to one extent or the other
11-05-01, 01:47 PM
#39
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The link: http://www.guarding-our-earth.com/de...il/chart.shtml
does seem to support that Amsoil has a lower ash content that conventional oil. Is the ash content what Mazda was worried about when not recommending synthetics? Probably, although I am guessing. Wouldn't it be great to get a Mazda rotary engineer's input on this forum?
I see the chart shows some synthetics have higher ash content than conventional. In our Forum, I've read that people doing a rebuild had very clean motors except crapped-up apex seals. I wonder if they used Amsoil or another synthetic.
Just changed my oil for the winter using 10w-30 Castroil, although after reading the Amsoil articles I may switch to synthetic. I still don't think 20w50 is good in my NorthEast climate. Again, I'd love to see some technical analysis.
Anyone else find more tech info on synthetics and ash? Most seem to be some variation of the above link (and older).
does seem to support that Amsoil has a lower ash content that conventional oil. Is the ash content what Mazda was worried about when not recommending synthetics? Probably, although I am guessing. Wouldn't it be great to get a Mazda rotary engineer's input on this forum?
I see the chart shows some synthetics have higher ash content than conventional. In our Forum, I've read that people doing a rebuild had very clean motors except crapped-up apex seals. I wonder if they used Amsoil or another synthetic.
Just changed my oil for the winter using 10w-30 Castroil, although after reading the Amsoil articles I may switch to synthetic. I still don't think 20w50 is good in my NorthEast climate. Again, I'd love to see some technical analysis.
Anyone else find more tech info on synthetics and ash? Most seem to be some variation of the above link (and older).
11-05-01, 02:11 PM
#40
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synthetics are superior, no doubt....the thing I am not convinced about is the "long drain" oil change interval issue....10,000+ miles? no way....there isn't an oil filter made today that will filter out blow-by and particulate contamination down to the 5-20 micron level, and do it for 10,000 miles...I don't buy it
even if you run synthetic, it will become saturated with particulate contamination of one type or another by 3,000 miles, just like a petroleum oil, to the point where continued operation will result in wear...I have seen enough research articles in "Roadracing World" and other places to substantiate this....racers change oil every race
even if you run synthetic, it will become saturated with particulate contamination of one type or another by 3,000 miles, just like a petroleum oil, to the point where continued operation will result in wear...I have seen enough research articles in "Roadracing World" and other places to substantiate this....racers change oil every race
11-05-01, 02:50 PM
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Originally posted by gsxr1000
the heat rejection may be an issue, I'd like to see some research on that topic, but it is balanced out by the fact that 10w-30 is pretty low vicosity for a rotary....I don't see how it can provide the same cushioning that 20w-50 gives, especially in an engine that runs as hot as the rotary does and gets beat to a pulp by turbos spinning at > 10,000 rpm
the heat rejection may be an issue, I'd like to see some research on that topic, but it is balanced out by the fact that 10w-30 is pretty low vicosity for a rotary....I don't see how it can provide the same cushioning that 20w-50 gives, especially in an engine that runs as hot as the rotary does and gets beat to a pulp by turbos spinning at > 10,000 rpm
Actually turbochargers operate in the 100,000 to 200,000 RPM range.
11-05-01, 05:51 PM
#43
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Use a lower weight oil in the winter. Something like a 10W 30 or maybe even a 5W 30. The greater the weight and colder the temps, the longer it takes for the oil to be pumped to the engines vital areas.
11-06-01, 09:26 AM
#44
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and the less protection it provides as soon as the car warms up!! you missed the whole point of this post and obviously didn't read any of it
it's a catch 22...that's why a heavier weight synthetic is the best solution (i.e. 15w-50 or 20w-50)....flows as good as a 10w-30 petroleum, cold (try it...you'll see, the pour point of a synthetic 20w-50 is still about -40 F) and blows it away in high temp performance (viscosity stability and thermal breakdown properties)
the WOT operating temps inside your engine are essentially unchanged, regardless of the ambient temps (within reason)
it's a catch 22...that's why a heavier weight synthetic is the best solution (i.e. 15w-50 or 20w-50)....flows as good as a 10w-30 petroleum, cold (try it...you'll see, the pour point of a synthetic 20w-50 is still about -40 F) and blows it away in high temp performance (viscosity stability and thermal breakdown properties)
the WOT operating temps inside your engine are essentially unchanged, regardless of the ambient temps (within reason)
11-06-01, 12:49 PM
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Here's some info I just got from Amsoil tech support (for what it's worth):
"We tested our products quite extensively in rotary engines and found it to work very well. We really know of no reason a high quality synthetic should not be used in these motors, after all synthetics do a great job in jet engines. Perhaps Mazda might be of more help. The repair manual that we use to help make product recommendations has no disclaimer about the use of synthetic motor oils. We’re also not sure about the pre-mix oil situation, but assume that whatever is being used in the crankcase should be used for the pre-mix. Once again, we are not familiar with this and Mazda should be consulted."
"We tested our products quite extensively in rotary engines and found it to work very well. We really know of no reason a high quality synthetic should not be used in these motors, after all synthetics do a great job in jet engines. Perhaps Mazda might be of more help. The repair manual that we use to help make product recommendations has no disclaimer about the use of synthetic motor oils. We’re also not sure about the pre-mix oil situation, but assume that whatever is being used in the crankcase should be used for the pre-mix. Once again, we are not familiar with this and Mazda should be consulted."
11-06-01, 01:57 PM
#46
Originally posted by Tim McCreary
Remember,
Synthetics have a higher ash content which results in increased deposits in the engine. For example, Castrol Syntec has 50% more ash content versus Castrol GTX.
Remember,
Synthetics have a higher ash content which results in increased deposits in the engine. For example, Castrol Syntec has 50% more ash content versus Castrol GTX.
So, in reality, the opposite is generally true with conventional oils having a higher ash deposit than any good synthetics(Castrol Syntec doesn't qualify). You are correct in your example: 0.85% GTX v. 1.2% Syntec.
11-06-01, 02:52 PM
#47
Originally posted by Tim McCreary
Synthetic oils have a higher %ash (50% higher in Castrol Syntec versus Castrol GTX) as well as a higher flashpoint which indicates that generally synthetics are not as well as dino oil for injection into the engine for lubrication of apex seals.
NOTE, even though higher operating viscosity is more protective, it also takes more energy (loss in power) to move the engine parts, resulting in poorer fuel economy.
Synthetic oils have a higher %ash (50% higher in Castrol Syntec versus Castrol GTX) as well as a higher flashpoint which indicates that generally synthetics are not as well as dino oil for injection into the engine for lubrication of apex seals.
NOTE, even though higher operating viscosity is more protective, it also takes more energy (loss in power) to move the engine parts, resulting in poorer fuel economy.
Your "NOTE" only applies to conventional oils. From Redline:
"The superiority of synthetics lies in the fact that a 10W40 synthetic can provide the high-shear protection superior to a petroleum 20W50...while providing a much lower viscosity...This lower viscosity produces more power and also better efficiency and fuel economy."
11-06-01, 03:38 PM
#48
In answer to the original question, you should really re-examine why you're not using synthetic oil. A good synthetic oil is superior in every way to conventional oil including Castrol GTX. If you talk to M2, they recommend the use of Redline 10w40 and offer it on their site. If you talk to Racing Beat, they recommend Royal Purple(another good synthetic oil). Also, winter doesn't really exist in LA. Still, the vastly superior pour point of synthetics would greatly help in any cold-start conditions.
Of course, even if you use synthetic oil in a rotary you still need to change the oil frequently. The only thing people have against using synthetics is the cost.
From Racing Beat's website:
"Racing Beat has been recommending the use of synthetic oils in rotary applications for several years. Our research has found that synthetic oils provide superior friction reducing between sliding surfaces, reduced foaming, and lower oil temperatures. We have tested several different synthetic oils and have found that...most offered improved wear and lower oil temperatures..."
Of course, even if you use synthetic oil in a rotary you still need to change the oil frequently. The only thing people have against using synthetics is the cost.
From Racing Beat's website:
"Racing Beat has been recommending the use of synthetic oils in rotary applications for several years. Our research has found that synthetic oils provide superior friction reducing between sliding surfaces, reduced foaming, and lower oil temperatures. We have tested several different synthetic oils and have found that...most offered improved wear and lower oil temperatures..."
11-06-01, 04:00 PM
#49
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good notes, JSpecFD
with the few moving parts of a rotary, seems logical synthetic oil would greatly extend the life of the engine under hard use
I'm going to try Mobil 1 15w-50 "tri synthetic" in my car next oil change....I just hate to change it out every 1500 miles like I have been doing with Castrol 20w-50...supposedly if you use a high effeciency filter (like the Mobil 1 filter for 10 bucks!) you trap more small particles that pass right through a conventional oil filter, but what about blow by and unburned fuel that gets into the oil? no filter can do anything about that stuff, and it wreaks havoc on the oil (petroleum or synthetic)
fram has this new "long life" filter that just came out, too
http://www.framx2.com/
with the few moving parts of a rotary, seems logical synthetic oil would greatly extend the life of the engine under hard use
I'm going to try Mobil 1 15w-50 "tri synthetic" in my car next oil change....I just hate to change it out every 1500 miles like I have been doing with Castrol 20w-50...supposedly if you use a high effeciency filter (like the Mobil 1 filter for 10 bucks!) you trap more small particles that pass right through a conventional oil filter, but what about blow by and unburned fuel that gets into the oil? no filter can do anything about that stuff, and it wreaks havoc on the oil (petroleum or synthetic)
fram has this new "long life" filter that just came out, too
http://www.framx2.com/
11-06-01, 06:53 PM
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GSXR1000,
First, I wish to apologize for the implication that all synthetics have higher ash content. I should have specifically said SOME SYNTHETICS. I was specifically referring to the Castrol Oil comparison (Castrol GTX vs. Castrol Syntec) in the independent test at this website. Castrol and Valvoline have the higher ash content than conventional oil. http://www.vtr.org/maintain/oil-overview.html
As you have referred to: Redline, Mobil 1, and Amsoil have little or no ash (based on the same website tests), so my gut feeling would be that these oils would not be detrimental in a rotary engine (my opinion). But looking at the more common store brand oils like Castrol and Valvoline, you can see on the chart the ash content of .80 for 5W30,.85 for 20W50 or 10W30, and 1.2 for 5W50 Syntec oil. Valvoline is similar with 1.0 for standard oils and around 1.5 for Synthetic oils. Their synthetic brands compared to their standard oils are 41-50% higher ash content. This was what my figures were based on. People tend to buy these oils over the Redline and Amsoil because of cost and availability reasons. I would not (in my opinion) use these store available synthetics in a rotary.
Second, there is some confusion about the term SHEAR. This has two definitions in the oil application. Shear – by definition is the frictional force overcome in sliding one “layer” of fluid along another as in any fluid flow. This is the friction part of oil. The higher the viscosity, the higher the shear or resistance to flow. Higher weight oils 20W50, 10W40 have higher shear or a higher resistance to flow. 5W30 and 10W30 have lower shear or a lower resistance to flow. Shear in this connotation is the fluid dynamics term.
The second definition of shear is the common term - to cut or separate. When oil velocity is increased, the amount of viscosity controlling molecules (viscosity index improvers or polymers) are “cut” or sheared permanently over time. This causes a loss in the viscosity of multigrade oils. Increase in temperature only increases the length of the molecules. Combined with increased velocity, this also causes a loss in viscosity.
With this said, the websites I mentioned in my earlier post refer to viscosity index improvers (polymers) that are added to oils. They are the molecules that cause the 10W or 20W oil to act like 30, 40, or 50 oil when temperatures increase. This happens because the polymers unwind and elongate, slowing the oil down. GENERALLY, the higher the difference in the number, the higher the amount of polymers added to the oil to achieve the upper number. 10W30 generally has less polymers than 20W50, so there are less of them to shear cut causing a reduction in actual viscosity. From the same website: “AMSOIL can formulate their 10W-30 and 15W-40 with no viscosity index improvers but uses some in the 10W-40 and 5W-30. Mobil 1 uses no viscosity improvers in their 5W-30, and I assume the new 10W-30.” So not all oils use them (NOTE THESE ARE ALL SYNTHETIC OILS IN THE QUOTE, NOT CONVENTIONAL). If they do not use them, then viscosity breakdown is not really an issue. If you use these oils and you see viscosity breakdown, there is probably something else going on like fuel contamination thinning the oil.
Now it is time to make the case. Shear (Friction) is proportional to the Shear Rate (Velocity). The higher the velocity, the higher the shear (friction). The shear (friction) as well as close proximity or contact of engine parts causes shear(cutting) of the polymers. At a given temperature, say 70 degrees Fahrenheit, the polymers are short. At a given velocity, say 500 rpm, the amount of shear(cutting) is minimal(possibly negligible). At the same speed and a higher temperature, say 250 degrees Fahrenheit, the amount of shear(cutting) is increased slightly because the polymers are elongated due to temperature elevation, but still not much because the amount of shear(cutting) of the polymer is speed dependent. Now take this engine to 8,000 rpm. Speed is drastically increased which causes an increase in shear(friction). An increase in shear (friction) causes an increase in shear(cutting) of the polymers added to the oil. This causes the viscosity breakdown of the oil.
Now remember, the amount of shear(friction) is dependent on the viscosity of the base oil. So 10W oil has a lower viscosity, therefore a lower shear(friction). With a lower shear(friction), you have lower shear(cutting) of the polymers. Higher viscosity oils have higher shear(friction) which equates to higher shear(cutting)of the polymers Oils with a higher polymer content like 20W have a higher chance of viscosity breakdown becuase the frequency of cutting the polymers is increased due to the increased number of polymer molecules.
To understand shear (cutting) due to speed increase, use this example: Silly Putty. If you pull it slowly, the layers slide over each other and the putty stretches. Now pull quickly, and the putty breaks or shears(cutting) and the putty splits into two pieces.
Summary:
So, the higher the temperature, the higher the viscosity, the higher the polymer content, the higher the chance of viscosity breakdown.
Comparing 10W30 to 20W50, you will see that there is a higher chance of viscosity breakdown in the same engine under the same conditions for the heavier weight oil.
NOW UNDERSTAND, the only comparison to Synthetic oils that I was making was in Ash content, not performance. I have clarified this mistake and should have quantified it better. Your referrals in your reply were aimed at Redline and Amsoil data which are both synthetic oils. The discussion originally revolved around 10W30 versus 20W50 conventional oil.
Tim
First, I wish to apologize for the implication that all synthetics have higher ash content. I should have specifically said SOME SYNTHETICS. I was specifically referring to the Castrol Oil comparison (Castrol GTX vs. Castrol Syntec) in the independent test at this website. Castrol and Valvoline have the higher ash content than conventional oil. http://www.vtr.org/maintain/oil-overview.html
As you have referred to: Redline, Mobil 1, and Amsoil have little or no ash (based on the same website tests), so my gut feeling would be that these oils would not be detrimental in a rotary engine (my opinion). But looking at the more common store brand oils like Castrol and Valvoline, you can see on the chart the ash content of .80 for 5W30,.85 for 20W50 or 10W30, and 1.2 for 5W50 Syntec oil. Valvoline is similar with 1.0 for standard oils and around 1.5 for Synthetic oils. Their synthetic brands compared to their standard oils are 41-50% higher ash content. This was what my figures were based on. People tend to buy these oils over the Redline and Amsoil because of cost and availability reasons. I would not (in my opinion) use these store available synthetics in a rotary.
Second, there is some confusion about the term SHEAR. This has two definitions in the oil application. Shear – by definition is the frictional force overcome in sliding one “layer” of fluid along another as in any fluid flow. This is the friction part of oil. The higher the viscosity, the higher the shear or resistance to flow. Higher weight oils 20W50, 10W40 have higher shear or a higher resistance to flow. 5W30 and 10W30 have lower shear or a lower resistance to flow. Shear in this connotation is the fluid dynamics term.
The second definition of shear is the common term - to cut or separate. When oil velocity is increased, the amount of viscosity controlling molecules (viscosity index improvers or polymers) are “cut” or sheared permanently over time. This causes a loss in the viscosity of multigrade oils. Increase in temperature only increases the length of the molecules. Combined with increased velocity, this also causes a loss in viscosity.
With this said, the websites I mentioned in my earlier post refer to viscosity index improvers (polymers) that are added to oils. They are the molecules that cause the 10W or 20W oil to act like 30, 40, or 50 oil when temperatures increase. This happens because the polymers unwind and elongate, slowing the oil down. GENERALLY, the higher the difference in the number, the higher the amount of polymers added to the oil to achieve the upper number. 10W30 generally has less polymers than 20W50, so there are less of them to shear cut causing a reduction in actual viscosity. From the same website: “AMSOIL can formulate their 10W-30 and 15W-40 with no viscosity index improvers but uses some in the 10W-40 and 5W-30. Mobil 1 uses no viscosity improvers in their 5W-30, and I assume the new 10W-30.” So not all oils use them (NOTE THESE ARE ALL SYNTHETIC OILS IN THE QUOTE, NOT CONVENTIONAL). If they do not use them, then viscosity breakdown is not really an issue. If you use these oils and you see viscosity breakdown, there is probably something else going on like fuel contamination thinning the oil.
Now it is time to make the case. Shear (Friction) is proportional to the Shear Rate (Velocity). The higher the velocity, the higher the shear (friction). The shear (friction) as well as close proximity or contact of engine parts causes shear(cutting) of the polymers. At a given temperature, say 70 degrees Fahrenheit, the polymers are short. At a given velocity, say 500 rpm, the amount of shear(cutting) is minimal(possibly negligible). At the same speed and a higher temperature, say 250 degrees Fahrenheit, the amount of shear(cutting) is increased slightly because the polymers are elongated due to temperature elevation, but still not much because the amount of shear(cutting) of the polymer is speed dependent. Now take this engine to 8,000 rpm. Speed is drastically increased which causes an increase in shear(friction). An increase in shear (friction) causes an increase in shear(cutting) of the polymers added to the oil. This causes the viscosity breakdown of the oil.
Now remember, the amount of shear(friction) is dependent on the viscosity of the base oil. So 10W oil has a lower viscosity, therefore a lower shear(friction). With a lower shear(friction), you have lower shear(cutting) of the polymers. Higher viscosity oils have higher shear(friction) which equates to higher shear(cutting)of the polymers Oils with a higher polymer content like 20W have a higher chance of viscosity breakdown becuase the frequency of cutting the polymers is increased due to the increased number of polymer molecules.
To understand shear (cutting) due to speed increase, use this example: Silly Putty. If you pull it slowly, the layers slide over each other and the putty stretches. Now pull quickly, and the putty breaks or shears(cutting) and the putty splits into two pieces.
Summary:
So, the higher the temperature, the higher the viscosity, the higher the polymer content, the higher the chance of viscosity breakdown.
Comparing 10W30 to 20W50, you will see that there is a higher chance of viscosity breakdown in the same engine under the same conditions for the heavier weight oil.
NOW UNDERSTAND, the only comparison to Synthetic oils that I was making was in Ash content, not performance. I have clarified this mistake and should have quantified it better. Your referrals in your reply were aimed at Redline and Amsoil data which are both synthetic oils. The discussion originally revolved around 10W30 versus 20W50 conventional oil.
Tim