tomk said:
generally, the oil is supposed to look dark and used when it comes out?
if it doesn't, then all the stuff that makes it look dark and used is staying on surfaces inside your engine instead of coming out when you drain it?
Unless there's nothing in the engine that's causing it to turn dark. A fresh engine with regular oil changes using high quality oil won't generally darken too much. It's only contaminated oil that darkens.
In theory, if there were no contaminants introduced to the oil, it could last indefinitely. Look at a propane fueled vehicle?The oil is as clean as the day it's dumped in 10,000 miles later. There's little to no contamination with propane fuel as it burns so cleanly.
Our race motor got broke in on Schaeffer's 20w50, and it gets changed every 4th-5th race (gross overkill), and now 2 1/2 years later, when the valve covers were pulled to adjust rocker arms, the heads and valve covers were as clean as the day that engine was assembled. This engine runs 110 octane leaded race fuel, and has seen coolant temps upwards of 265? regularly.
