[QUOTE]Originally posted by MacGyver
I believe it was Consumer Reports that did a several year long study on the properties of dino versus syn oil.

 

I don't agree that general passenger car use is as severe as a taxi. While you are essentially correct about the heat thing, most people drive their cars enough that the oil temp reaches over 200 degF, which will boil off most of the water in the oil. And it does not occur from the cooling down cycle, it tends to occur more from the warming up cycle, since the cold engine bore will cause imperfect combustion and one of the byproducts of said imperfect combustion is H20. The water indeed can react with phosphorous and sulfur to form weak acids, which if left in the oil too long, can be damaging. But remember that oils contain acid neutralizers, eveidenced by the TBN, or total base number. The higher, the longer the oil can withstand acidification and oxidation.

Oxidation is primarily the reactive combination of high temperature and oxygen. This will cause breakdown of the VI improvers in oil, and boil off the lighter factions - even synoils will experience viscosity thickening due to volatility. The result of oxidative processes is sludge and thickening, and even synoils will leave deposits in the high temperature areas like oil control ring lands.

Also, mineral oils are formed by refining, which is essentially a series of heating cycles which cause the aliphatic compounds and asphalts in crude oil to be released and skimmed off. When in a hot engine, this process tends to reverse, causing some de-refinement, and release of the contaminants never quite removed from mineral oils.

So even with suburban start/stop cycling, I would side with MacGyver that taxi cab use is just about the most brutal use there is.

Regardless, back to the point - modern oils are terrific, and most people overchange them. The 3K oil change is for the most part an anachronism.

 

What is amsoil again?

 

http://www.amsoil.com/