quote:If it thickens enough, any oil will cause sludge. I don't know for sure if a lousy 5W-30 or a lousy 20W-50 dino oil is more likely to thicken under the same conditions, but I expect the 5W-30 to go bad faster.
Anyone vote for running too thin an oil for too long an interval?
quote:"using the wrong grade" Would that be lighter, or heavier than the mfrs recommended grade?
Originally posted by Jimbo: There are at least two different types of sludge. One type is oil coking or thickening from high temperature oxidation. This can be caused by over-extending drain intervals and/or using the wrong grade.
quote:That's NOT sludge at all. It's merely a harmless goo consisting of condensation of water and oil vapor that forms on cooler surfaces - most likely when the weather turns cooler and the car's not driven far enough to thorougly warm the oil and cook off accumulated moisture. Unfortunately that's the same scenario that's likely to form real sludge, too, because of acid/moisture buildup in the sump and that combo's chemical interaction with oxidation insolubles as the detergent package is depleted from overuse.
Originally posted by Jimbo: The other type I have seen is soft, mayonnaise-like sludge from moisture.