Tim McCreary

JspecFD,

In my post above, you can see that I have clarified my mistake about ash content. My statement was not false, but true. I meant to say some synthetics and was specifically referring to Castrol and Valvoline synthetics versus their conventional brand oils. I was not trying to compare Joe-Shmo’s oil with synthetics, as that would not be fair.

You stated -- Secondly, Castrol GTX itself doesn't burn cleanly as well as most other conventional oils (Exxon High performance, Havoline Formula 3, Kendall GT-1, Pennzoil GT Perf., Unocal, havoline, etc.). They're generally around 1% by comparison. -- If you would have read the chart on the website I posted, you would see that Castrol GTX was at .80 and .85 which is lower than the 1% you listed above for the oils you listed above. (Exxon High perormance=.70, Havoline Formula 3=1.0, Kendall GT-1=1.0, Pennzoil GT Perf=.90, Unocal=.74, Havoline=??repeat). Actually 22 oils listed had lower than .85 ash content. Of those 22, 12 are the synthetic oils AMSOIL, MOBIL 1, and REDLINE. This leaves 12 better out of a list of 72 oils tested. This makes it one of the cleaner burning oils in the comparison, not worse. Yes, in comparison (apples to oranges), conventional and synthetic oils compared to Amsoil, Mobil 1, and Redline do have a higher ash content. Saying that Castrol Syntec or Valvoline Synthetic are not good synthetic oils is an unfair statement. They have additives for other reasons that make them better for other applications versus the three “good synthetics” listed above. If you would like to say the three are “good rotary engine synthetic oils”, I would most definitely agree to that statement. Most likely, the “other” additives in the store brand synthetics are contributing to the higher ash content (opinion, opinion, opinion).

In your next post, you state that the synthetic oils have a higher flash point, which provides better lubrication. Please provide information relating flashpoint to lubrication qualities of oils. If I am not mistaken, flashpoint has nothing to do with the lubrication qualities of the oil. Well I guess if the oil reaches flashpoint and burns off, there is no oil to lubricate. I guess then it would be better. The lubrication qualities of oil is a reference to how well it reduces friction between moving parts in an engine. Flashpoint is an indication of the temperature at which the oil itself will vaporize and burn.

Your quote: "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." Step outside the sales pitch world and analyze this quote. Synthetics provide high-shear (cutting) protection superior to ANY equivalent petroleum oil (10W40 vs 10W40 synthetic) because they need little or less polymers to achieve the higher weight listed. Also, 10W40 conventional ALSO has a lower viscosity than 20W50 conventional. Remember, Viscosity is Viscosity, whether synthetic or conventional. 10W30 Synthetic viscosity is equal to 10W30 Conventional viscosity. Now after time and use, the amount of viscosity breakdown in conventional is generally higher due to the higher polymer useage. Note that they do confirm my statement that lower viscosity oil produces more power and better fuel economy. This again holds true with any oil higher viscosity versus a lower viscosity. This is because viscosity is a measure of shear (friction) which is the internal friction of the fluid itself.

Remember now the statement can be changed to: 10W30 petroleum 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. This statement holds true for the same reasons listed above WHICH IS EXACTLY WHAT THIS POST IS ALL ABOUT. If you are going to use dino juice, use 10W30, not 20W50. It is more fuel efficient, does not rob power overcoming viscous friction, and is better flowing at cold start (increasing protection at engine start-up). Cold start is referring to a cold engine start, not necessarily cold outside temperature. Although the outside temperature will be the temperature of your car engine after setting overnight.

Also remember, viscosity of the higher number in a multigrade oil is based on the temperature at 100 degrees Celsius (212 degrees Fahrenehit). Above that, all bets are off (no firm data). If you are talking about how well the viscosity holds up at high temperatures, I can find no data on this. The only thing related to this is that most all synthetics have a higher flash point, thus will maintain integrity at a higher temperature.

Your last quote: “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.” I AGREE WITH THIS TOTALLY. After going through this discussion and research data, I would highly recommend using one of the three “good rotary synthetic” oils listed above over any grade equivalent conventional oil. The biggest concern appeared to be ash deposits from injecting oil into the engine. All posts that I have read referred to how synthetics do not burn cleaner. You have definitely helped point out that some synthetics do burn cleaner and are better for your engine. Thank You.

Tim

PS. All opinions expressed by Tim McCreary are his personal opinions. Anyone who disagrees with them has a right to come to his house and lash him 50 times with a wet noodle. Anyone who agrees with him should not speak up for fear they may be labeled psychotic and hauled away.

JspecFD

iTrader: (2)

Tim: Seems like we're on the same page for the most and agree on everything. Just some minor semantics to correct. I didn't comment on the dino oil only comparisons since we're in agreement there.


Actually, looks like you didn't read my reply. If you did, you'd note that I cited the specific numbers you referred to and agreed with your Castrol Syn v. GTX ash assessment. Also, when you see the words "generally around" thats known as an approximation. By listing specific numbers, you're only proving my assessment to be correct(note the use of 1 significant figure)

Regarding flashpoint, it seems like you're contradicting yourself. First you state that "higher %ash...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" With a 0% ash deposit left from a good synthetic, please quantify why the higher flash point would impede lubrication.

Since you had some question about Viscosity and shear at higher temperatures, here's a table that someone else alluded to earlier:




Thus, a "10W40 synthetic can provide the high-shear protection superior to a petroleum 20W50" So yes, 'all bets are off' on the dino oil at higher temps and shear conditions because they lack viscosity stability.

Tim McCreary

JspecFD, gsxr1000,

I mis-read your quote. I thought you were saying Castrol GTX was higher compared with the other oils you had listed. Now that I read it again, I can see where you were including them all in a less than 1 % ash comparison. Sorry.

I agree that it appears I have contradicted myself. I was using the Castrol comparison since the three “Good Rotary Engine Synthetics” do not have conventional equivalents within their brand name. The higher ash content will no doubt leave a higher deposit inside the combustion bathtub. The higher flashpoint will cause the oil to not burn as easily, therefore leaving a higher chance of residual oil after the combustion cycle. Now it is only my speculation that increased unburned oil would collect and promote carbon buildup. A higher flashpoint would not directly impede lubrication, but could cause increased buildup of carbon deposits. This is only my speculation based on the numerous posts I have read on the oil debates in rotary engines. (Now you think, if the oil does not have an ash content, how can it build carbon deposits? My only comment is that there is more than just oil in the combustion chamber. I am only suggesting that those additives in fuel and the residual of combustion would “stick” to the unburned oil promoting the carbon deposits. Not necessarily that the oil itself is the cause of the deposits.).

In an engine already running at operating temperatures, this should not be much of a problem as the temperature in the combustion bathtub would probably exceed the flash point of any oil (thus burning the oil). The problem would be at cold starts and cooling down after shut off. My friend had an engine set over winter, started it up at idle in the spring, and it locked up (carbon deposit fell off the one rotor face and wedged the apex and sidewall).

I can only comment on the high temperature protection or high load protection in opinions (logic) as I have no firm data to make a basis from. All things considered, the higher the flashpoint, the better the high temperature protection you would think, since the oil itself would not vaporize as easily.

Remembering that the oil is also a major part of the rotary engine cooling system, I would only suggest that the high temperature protection of oil should be based on its thermal conductivity. (How fast it can accept the heat from the engine and how fast it can dissipate the heat at the oil cooler). Since we have no data on this, I cannot make an educated guess as to whether any oil is better than another in this case.

High load protection…Hmmmm… Yes…and No… There are merits to using a thicker oil. The thicker oil would give a better “cushion” between moving parts. All oil thins out (varying degrees) as the temperature increases. The question then becomes what is my actual viscosity at operating temperatures? In my mind, I would use 10W30 and run a slightly lower temperature thermostat to keep things a bit cooler and a bit thicker. As someone else mentioned, the oil layer thickness and the viscosity play a big part in engine tolerances and flow of the oil throughout the engine. Remember, basing your argument on thicker is better, you probably should use 75W80 gear oil when the ambient temperature is above 80 degrees outside. But then the oil would not be suited for flow through the turbo chargers. Exactly the point with using any oils with viscosity not necessarily recommended by the manufacturer. We may not know what was put into the design and why. Mazda only recommended two different oil weights 5W30 and 10W30 for the 1993-95 RX7. I believe that they allowed 5W for colder climate startups. But both oils are limited to 30 at the upper limit for a reason. Many other cars that I have seen recommend 4 or 5 different oil viscosities for the same given temperature depending on the ambient temperature range. 1985 RX7 manual recommended oils viscosities are 5W20,5W30, 10W30, 10W40, 10W50, 20W40, and 20W50 (recommended from around 0 degrees Celsius and up) 1988 RX7 manual recommends all but the 5W20. When were synthetics introduced??? No warnings in these manuals for synthetic oils.

My opinion on oil changes. 3000 miles maximum with conventional oils. Synthetics could be longer. Remember that more damage occurs when the oil contaminants increase. It is the “dirt” and gas thinning viscosity in the oil that causes the damage. Assuming little viscosity breakdown, synthetic oil should be changed on a “dirty” basis. If I were going to run all synthetic, I would change oil filters at 3000 miles and oil change at 6000 miles as long as the oil stays clean to the appearance during the timeframe. If it becomes “black and dirty” or thins out quickly, I would change oil at 3000 miles. Changing oil sooner than 3000 miles is a personal preference. I think it would be a waste of money unless you really run the car hard and hot daily or you have definite fuel contamination. It definitely could not hurt though.

I am speculating ash content as this is what would cause additional carbon buildup in the engine. Mazda’s 1993 owners manual states “Synthetic oils will damage rotary engines. Be sure to use only nonsynthetic oil in your RX-7.” My understanding from a post I read once was that Mazda tested all synthetics and one oil did not work. Because they could not say, “Use all oils except BILL’S Junk Synthetic Oil, it will blow your engine” due to a lawsuit, they decided to not recommend any synthetics. Their statement does not specifically quantify “all synthetics”, you can take it from there. The burden of proof then falls on the oil manufacturer to prove his oil will not damage the engine. The post was supposedly an internal memo from Mazda or a paraphrased version of it.

Remember, if you are going to use synthetics, don’t use them on a new/rebuilt engine until after a break-in period. Even piston engines blow right after rebuild with synthetics.

As for me, my decision is to use 10W30 Castrol GTX until about 6000 miles on the new engine, then I am going to go with 3 quart Castrol and 1 quart Mobil 1 10W30. I will continue to change oil at 3000 mile intervals. The Mobil 1 will be for the turbo charger bearings. With a 25% mix, I think the chance of a failure is minimized and some of the benefits of synthetic are going to be utilized.

Tim