frank69m

Just got some Castrol GTX 20/50...then I realized, it is the winter time coming up...I live in California so I don't expect any snow, but can have cold startups in the morning...Should I stick with 20/50 or go for 10/30...and no synthetics or me...just good ole Castrol GTX

thatoneguy

I use 10W30 in the winter here. 20W50 takes forever and a day to warm up.

misdbman

I stick to the Owners manual. Since it get's cold here in DE, I usually run either 5w-30 in the winter. 10w-30 is ok also. Even though some of the tuners use 20w-50, Mazda does not recommend it.

Tim McCreary

misdbman,

I agree with you on the oil. If people are using 20w50, they are losing a little power with internal viscosity friction. I think people have been using it due to the extreme high temperatures in a rotary, but if you change your oil every 3k or less, chances are any oil will not show much viscosity breakdown.

Tim

f2racer

iTrader: (1)

Agreed here, run 10W30 all year in the suburban Boston area. It snows here for those that don't know (in fact it's snowed here already this year). As long as you change the oil frequently (2-3k), you'll be safe. I once changed the oil closer to 3k and even though the oil was cold when I did it, it poured out like water. Don't think it's the oil weight, more likely the abuse it gets from the rotary... Manufacturers haven't recommended using 20W50 in 20 years because it's pros (better protection when used in high heat conditions) are heavily outweighed by its cons (much less protection during the time that you most need it - starting).

AARotary

As of now I am using Castrol GTX 20W-50 now and I will switch over to 10W-30 when the weather is getting colder.

misdbman

I'm know that Mazda engineers put the motor through tons of testing prior to their oil selection recommendation. I run the recommended 10w30 all year. I just change it every 1500 miles. I think part of the problem is too much heat when you mod the engine, breaking down the oil. One of the recommended mods should be the second oil cooler.

Does anyone know what Mazda Motorsports recommends? I would be more likely to trust their racing division.

misdbman

I like Pettit but just remember that the rotary uses the oil to reject heat. Higher viscosity would cause a lower flow rate, rejecting more heat into the oil per volume. This would cause the oil to get hotter using 20w50. Synthetic is good but may build up deposits on the seals.

Just remember that Mazda builds test beds with many motors subjected to all temp and operating conditions. They have a very good reason for their viscosity recommendations.

I would personally add the 2nd oil cooler if you don't have one. The base and touring models are not designed for higher horsepower(rejecting more heat) and to be driven harder on 1 cooler.

wickedrx7

iTrader: (14)

I run 20-50 in the summer ans then 10-30 in the fall.
I have heard that sythetics are bad for rotories. I thought this was well known around the rotory world that sythetics are a no no. Well if you didn't know that you should, no synthetics.

wickedrx7

iTrader: (14)

I run 20-50 in the summer ans then 10-30 in the fall.
I have heard that sythetics are bad for rotories. I thought this was well known around the rotory world that sythetics are a no no. Well if you didn't know that you should, no synthetics.

misdbman

I'm just going to do a mind dump here and see where I get with this...

I am no expert on this subject, but seems to me that a higher viscosity just means that the oil is 'thicker', not that it is any less prone to breakdown. Granted you might get better cushioning, but a rotary does not have reciprocating mass to cusion. Higher viscosity means that less would get past the oil seals - good. Higher viscosity means that the oil injection would flow less - bad, especially on this REW motor which injects less oil than the 2nd Gen 13B's. Higher viscosity means that the oil used to splash inside each rotor would stay there longer(maybe good for longer time for heat transfer) but would not flow out of the rotor as fast (maybe bad if this oil is staying hotter). I think what would rule would be to keep the change in temps less between motor parts(especially since the rotory is a sandwich of dissimilar metals with different expansion\contraction rates). You would also want to keep the oil temps lower due to this same reason. Higher viscosity means less flow at startup. We've all seem the adds about most of engine wear at startup.

I think lower oil temps due to higher flow through the oil cooler and more oil injection rule out the benefits of higher viscosity. But I could be wrong - I have nothing but my conjecture to go on. Again, Mazda spent years testing the REW motor and came up with 10w30. I would go with the designers of the motors. Maybe so many of us pop motors using this higher viscosity?
Also, some of the newest cars recommend 5w20, a lower viscosity...

Tim McCreary

I am no expert either, but I did find the following websites for information. My determination (opinion based on data and information given) is that 20W50 is NOT AS GOOD AS 10W30 for the RX7 Rotary Engine car based on the information they gave me.

http://www.vtr.org/maintain/oil-overview.html
http://www.engineoilinfo.com/voxpop19.sht
http://www.castrolusa.com/products/p...uct_category=1
http://www.oilanalysis.com/dictionar...lphasearch=%25

Some items that I took note to:

Multi Viscosity Oils - Polymers are added to a light base (5W, 10W, 20W), which prevent the oil from thinning as much as it warms up. At cold temperatures the polymers are coiled up and allow the oil to flow as their low numbers indicate. As the oil warms up the polymers begin to unwind into long chains that prevent the oil from thinning as much as it normally would.

Oils that do not contain special Viscosity Index Improver additives, such as single grade oils, will experience little or no permanent viscosity loss. IE - the base oil will not breakdown viscosity lower than the stated number

Viscosity Index is an empirical number indicating the rate of change in viscosity of an oil within a given temperature range. Higher numbers indicate a low change, lower numbers indicate a relatively large change. The higher the number the better. This is one major property of an oil that keeps your bearings happy. These numbers can only be compared within a viscosity range. It is not an indication of how well the oil resists thermal breakdown.

Thermal Breakdown - IE- FLASHPOINT as alluded to in the Castrol Website indicates the oil being heated to the flashpoint and "Burning". Thermal breakdown is the reaction of motor oil to high levels of heat in an engine. See also Volatility. Volatility - the degree and rate at which a liquid will vaporize under given conditions of temperature and pressure. Most oils start to break down at around 400 degrees (generally) Thermal energy does not breakdown the oil, it vaporizes or burns the oil.

Viscosity Breakdown - when the polymers added to the oil start to break down and shear (cut due to friction) causing the oil's higher viscosity number to be reduced. IE Viscosity breakdown of 20W50 would end up being something like 20W40 or 20W30. The lower number is the base viscosity (20) and does not break down. Just the polymer additives to make it act like 50 breakdown causing the oil to be thinner at higher temperatures. Oils with less polymer additives are better. Generally, the lower the difference in the two numbers, the less polymers added. IE - 10W30 has a difference of 20 where as 20W50 has a difference of 30. High shear forces can crush lubricating molecules or even break them in half. These damaged molecules cannot thicken properly and may not provide the protection you need. NOTE THAT OIL VISCOSITY CHANGE DOES NOT OCCUR TO THE BASE OIL, BUT HAS EVERYTHING TO DO WITH THE POLYMERS ADDED TO THAT BASE. TEMPERATURE CHANGES THE POLYMER, NOT THE OIL, TO GET THE VISCOSITY CHANGE FROM THE LOWER NUMBER TO THE HIGHER NUMBER IN A MULTIVISCOSITY OIL. TEMPERATURE DOES NOT CAUSE VISCOSITY BREAKDOWN, ONLY HIGH SHEAR FORCES CAUSE THE POLYMERS TO BREAK DOWN CAUSING REDUCED VISCOSITY.


% sulfated ash is how much solid material is left when the oil burns. A high ash content will tend to form more sludge and deposits in the engine. Low ash content also seems to promote long valve life. Look for oils with a low ash content. 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.

I hope this changes some people's minds and misconceptions about oil and the oil viscosities.

Tim

bbr1

There have been MANY debates on 10W-30 vs 20W-50 on the email list and on this forum in the past (as well as debates on dino vs synthetic oil ). I think that the only consensus we've achieved is on the frequency of oil-changes - do them as often as possible.

I personally stick with Castrol GTX 10W-30 and change the oil every 1,200 - 1,500 miles. The oil does seem to have a lot of fuel dilution at that point....

misdbman

Excellent technical info from Tim. Just trying to have a technical discussion vs. so and so say to do this so we should.

Mazda put millions of bench miles on the REW motors in addition to real world testing under very hot and cold conditions. All this was done prior to their viscosity recommendations. The recommended viscosity was used to size the diameters of oil passages, flow rate, oil pump capacity\pressure, the oil cooler size, etc.

By running 20w50, you are doubling the viscosity when the oil is cold and by more than 50% when hot. This will screw up all the hydraulic equations which were used to design the lubrication and cooling of the REW motor.

I still argue that flow rate of the oil is more important than higher viscosity. Higher viscosity will lower flow rate and cause higher oil temps locally(hot spots). One would be the turbo bearings. Higher viscosity just means that is is 'thicker', not less prone to breakdown.

Anyone just out of engineering school or do hydraulics for a living? It's been to long ago but I remember viscosity being a primary variable in hydraulic calculations. How would doubling the viscosity affect the flow for a particular diameter oil passage?

My argument is that higher viscosity means lower flow rate. Do you want less oil splashing against the insides of the rotors or more? More should have a greater cooling affect on the rotor - this would be a good discussion for someone who is an expert on heat transfer.

I think Pettit's and other tuner shop recommendations have merit dependent on how the car is used and your geographic location. Many of these shops are in hot regions of the country - their cars may not need the 10w viscosity. Their recommendation may come from running the motor continuously at high rpm - this may parallel the reasoning for underdrive pulleys eliminating coolant cavitation. Their recommendation for running synthetic during races but not street seems wise as well. This synthetic oil during races comes with a recommendation for gas\oil additive. This seems wise since the oil injection system is adding high-ash content synthetic and need to be supplemented.

Since my car is driven like a hard street car(not race car), this should fall into the operating parameters which Mazda envisioned. Hence I would follow their recommendations.

Any hydraulic\heat transfer engineers out there?

JConn2299

10w-30 Castrol GTX all year aound.

f2racer

iTrader: (1)

But yet they couldn't figure out that the downpipe was a really stupid idea, or the cooling system was inadequate... The list goes on and on. I wouldn't give Mazda all that much credit. Sure they've probably fixed the majority of crap with the latest Japanese only RX, but 3 years of RXs here kill the repuation of a truly great car.

Tim McCreary

I agree that the downpipe was a stupid idea when you think of longevity of the turbos and engine, but remember one thing: WHO REQUIRED MAZDA TO INSTALL IT??? The USA Emissions Testing OR corporate dictated emissions numbers. Remember back in 1974 when all the US cars lost all power? They had to put cats on and all the emissions crap. In hind site, we could easily say the same thing about those cars and their dependability. How many people plugged their cats only to poke a hole in it and let all the beads out? To them, it is the same as our downpipe. Don't put all the blame on Mazda for this one. Given time, I think Mazda would have changed this. And in fact, if you look at the new RENISIS engine, I think they have. Too bad demand for the RX7 dropped and the price jumped.

Don't forget, Mazda engineers went through many reworks to get the weight of our cars to the absolute minimum. Good examples are: Almost too short spark plug wires to save grams of weight, pressure cast aluminum rims that weigh about 15# and are stronger than regular aluminum, aluminum suspension components, twin bumps in the roof to improve aerodynamics, aluminum brake and clutch pedals, etc, etc. My belief is that the true engineers of the car probably did not want the pre-cat, but corporate dictated to meet cold start emissions standards for a cleaner vehicle for the US. (HMM... DOES J-SPEC ENGINES HAVE PRECATS??) Think of it this way. If the precat did not exist, the car may never have been allowed in the USA. That would have been bad.

As far as the cooling system, Supra TT had the same problems (I believe I read somewhere in comparison testings) For spirited street driving, the cooling is just adequate. Serious running cars will need to upgrade.

I personally have faith in the true Mazda Engineers that brought the car to reality. I don't have much faith in our local Mazda dealers though, as they don't care SQUAT about our cars (a few exceptions out there so noted). They care about making money.

One other note. People have said they drain their oil and it runs out like water after only 1500-3000 miles. Much of this appears to be from unburned fuel getting back into the oil system and thinning the oil out, not necessarily thermal or shear breakdown. Much of this comes from people who have modified and run the furel mixture rich to prevent detonation. People should note if the oil smells like gas when this happens. This would also indicate that the sealing integrity of some of their seals inside the engine may be marginal. Probably good for compression, but when the unburned fuel is wiped around from exhaust to intake side, it works its way in.

Tim

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. Mazda did do some things right with the REW but they also created a lot of problems that tuners eventually had to fix. AST being one of them. Mazda's precat has been a consistent problem with clogging and killing FDs everywhere. Rubber hoses used in a "surface of the sun" heated engine bay. There have been too many problems with the REW to trust many things that Mazda "recommends" Yeah, they have everything ironed out with the new FDs in Japan. Why didn't they install a 2nd oil-cooler in the base and touring. Did they actually think that someone with a base or touring would not run it as hard as an R1 or R2? Mazda might have done a lot of testing but look how many "engine rebuilds" you see on all FDs (even stock ones) because of some things that Mazda could have done. Either oil will work fine. I have heard not to switch back and forth and just to stay with one so you might not spin a bearing.

bbr1

Barry,

Unfortunately the lack of second oil-cooler on base and touring models is to allow an auto tranny cooler to be mounted, as I'm sure you're aware. I guess what Mazda should've done is offered two oil-coolers on all manual-trans cars and not just all R-models....

That was one of the reasons why I went for an R1...

Pele

iTrader: (28)

I usually use Castrol GTX 20w50, but I make up for it by adding a quart of Marvel's Mystery oil to 4 qts of oil.

10w30 with MMO was too thin in my opinion. I kinda compare it to how well it runs off the dipstick with basic 10w30 being the standard. Slower than 10w30, too thick. Runnier than 10w30, too thin.