Engine Oils!

[Anthony]

Comments by a GM Engineer taken from a yamaha motorcycle web site.

“I am a newbie to this site...LOL...but not a newbie. 33 years at GM and counting....the last 20 in engine development. If you want to see what I've been working on the last few years score the May issue of Hotrod Magazine and read the article on the Supercharged Northstar for the STS-V/XLR-V. “

A. Why change your oil ?

Keep in mind that there are a lot of reasons to change the oil. (1) Oil oxidizes with time and temperature.
(2) Oil gets contaminated with combustion by-products, oil gets contaminated with soot from blowby, oil gets contaminated with fuel and water...particularly during cold starts, acids form in the oil, oil gets contaminated with dust/dirt/debris, and the anti-oxidants/anti-acids/detergents/dispersant additives deplete with time and engine revolutions. (3) The anti-wear additive in the oil (the "zinc" or ZDP) gets depleted with engine revolutions,

(1) Synthetic oil addresses the oxidation as it will handle higher temperatures but that is about the only advantage of synthetic. If oxidation were the only reason to change the oil then synthetics would have an advantage in terms of life or extending the drain intervals. Unfortunately, oxidation due to temperature is RARELY the determining factor for the drain interval so any advantage synthetics might have in this area are moot.

(2) The water from combustion byproducts/blowby combines with the sulfur in the fuel in blowby to form sulfuric acid over time, so oil acidity slowly increases with time and miles, and synthetic oil does nothing different to prevent this. You have to change the oil before the anti-acids in the oil additive package are overwhelmed.

(3) Synthetic has the same amounts of ZDP as conventional oil, which is depleted over time.

So, in short, using synthetic does NOTHING to allow a longer drain interval. As compared to conventional oil, synthetic has the same problem with fuel and water contamination, same problems with other contaminates including soot, same problem with acid buildup, ZDP depletion, etc.... All reasons why synthetic oil does NOT allow longer drain intervals. I would recommend sticking to the recommended drain intervals even if you use synthetic oil.

As an aside, you will find that "racing" has little to do with passenger cars or street bike engines. Just because something works on racing cars or is used by racing teams does not mean it is good or applicable to everyday use on the street. The marketers like to make you THINK that racing means good but that is just marketing and an image. Look at the facts, first.

Like I said, the synthetics are excellent products. You certainly are not going to hurt anything using them... Just be aware that in most all conventional engines in cars and street bikes the use of synthetics is just not required. The areas that synthetics are "better" is far outside the normal operating range of the oil so that area or advantage is just not used nor needed.

My main reason for posting on this thread was not to run down synthetics at all...just make sure that people understand that the idea of extended drain intervals with synthetics is not really true and not something that they should be fooled into believing. "Extended" means a lot of different things to different people. If someone reads Amsoils BS and thinks that they can run their FJR 25K between oil changes they are being sadly mislead. In explaining why synthetics do not necessarily provide additional service life it is hard to not touch on their limitations and compare them to conventional oil.


The data that I see indicates that, under normal use, conventional oil functions perfectly well. When I see an engine run for 300 hours at full throttle/max load on an engine dyno with conventional oil and then at teardown the bearings are not even touched and other wear surfaces are fine it is hard to understand just how much "better" synthetic oil could have run....LOL LOL I have seen LOTS and LOTS of engines run like this and somehow, miraculously, the engines always look fine with conventional oil. And we don't even add Lucas or Slick50 or ZMax or ???? LOL LOL