In Reply to: Bob, are you sure **/30w oil is adequate for posted by more on September 12, 2000 at 12:26:01:
Synthetic engine oil protects better than petroleum so if the car maker suggested using a 20W-50 (for example) petroleum oil under high ambient temperature conditions, synthetics will accomplish the same job, better and easier using only a 30 weight.
Engine oil has friction due to its viscosity and must be forced to (and through) many parts of the engine. These oil passages are designed by the engineers to provide adequate lubricate to flow to various areas. The thicker an oil is, the more friction there is. Also, the thicker the oil is, the less cooling there is.
The list of reasons and thoughts are quite long for using a lighter weight "synthetic" oil. Keep in mind BMW and all the rest of the car makers suggested years ago (ex.'95) that a thicker oil like 20W-50 "petroleum" oil be used in high ambient temperature conditions. The reason; petroleum oil does not have near the lubricating qualities that synthetic oil does. Also, petroleum oil doesn't have the ability to protect as long, operate in nearly the high engine temperatures, clean as well, disperse contaminates as well, guard against high pressure and high sheer breakdown, protect against metal-to-metal contact and reduce friction of the moving parts. That's why the car makers only a few short years ago suggested a higher viscosity "petroleum" oil.
Bearing clearances are designed more for a 30 weight oil than a 50 weight oil. A thicker weight oil can and will "bump-up" or "ramp-up" while trying to be forced through bearing clearances that are tightly spaced. When this happens, oil starvation can result and damage can be the result! Engine oil can sheer or tear when thick and forced under pressure.
I might add if you had a 1,500 horsepower drag engine, the clearances would have much different spacing and a thicker oil "might" be used depending on how the entire engine was built. Using a a true racing oil, without any wear fighting zinc properties or detergent chemicals added should not be used for a street driven engine but many people elect to use it because it they thinks it's better. These are usually single weight oils defined for racing only but some still decide to use it because they think they have a "racing engine"!
I believe you'll find using a 0W-30 or 5W-30 synthetic oil for both everyday use as well as auto-X and track events will allow you the following: better overall engine protection, less wear, cooler operation, less engine friction, faster revs and more horsepower, less cold start-up wear and a longer lasting battery.
One last thing, independent testing has determined that engine failure due to oil quality itself is virtually nil. Failures that are due to lubrication or lack of it is only seen because of contaminated oil (by simply age, foreign particles, water, fuel or combustion by-products) or lack of oil (starvation) from less than necessary oil levels.
When was the last time you saw or heard of an engine failure due to the oil itself. The "synthetic" oils today are so far advanced from the oils just a few years ago that the car markers are only now beginning to catch up!
cars that frequently participate in auto-x/track events? I was told the higher the upper number the better for these extreme conditions? After going nuts trying to find a good 5/40 synthetic oil, I decided to go with castrol syntec 5/50 (seemed to have the best of both worlds...cold start up protection as well as protection against extreme stress loads/high temperatures). Given the availability of 0 or 5w/30w synthetic oils, I would rather use them, but, if they arent adequate for frequent auto-x/track events, I guess I have no choice. Your thoughts???