Causes of Sludge

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BITOGers,
Even after spending more than 8 months on this forum, I still do not understand the causes of sludge. Please educate me on this subject matter.

Michael
 
Several things can cause sludge. # 1 is not changing the oil when it needs to be changed. That, of course, depends on the engien and the oil. Other things, like a stuck open thermostat, can cause sludge too because the engine runs too cold and the oil doesn't get to temp. Extreme heat can cause sludge as well (case in point, Toyota).
 
Short trips KILL. We have a 93 Chevy K1500 5.7 tbi. Has major sludge under the rocker covers. Bought at approx 80,000 miles ~ 113,000 miles now. Dino oil always changed at 3000miles or less.
 
quote:

Originally posted by Steve S:
Not changing your motor in a timely manor is the cause of sludge.

How often should one change the MOTOR?
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or should I just change the motor OIL?
 
quote:

Anyone vote for running too thin an oil for too long an interval?

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.
 
pscholte - Anyone vote for running too thin an oil for too long an interval?

Doubt the viscosity has much to do with it, the OCI and add pac is much more important.
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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. The other type I have seen is soft, mayonnaise-like sludge from moisture. This can be casued by short trip driving, a plugged breather system or coolant leaking into the oil. Using non-detergent oil in a street-driven vehicle may also cause this.
 
quote:

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.

"using the wrong grade"
Would that be lighter, or heavier than the mfrs recommended grade?
 
As generalization poor engine design. Also over extended oil change intervals or improper spec'ed oil. The over extended time limit is controlled by engine design and of course lots of other variables.
 
Never changing out your PVC valve can lead to sludge. Just because they still rattle doesn't mean they are still working correctly.
 
The major cause of sludge in a diesel or gasoline engine is the oil on the cylinder wall burns and either carbonizes, becoming a hard particle, or it polymerizes, becoming a thick fluid. This burned oil then gets back into the sump. The carbon particles will attract water and acids from blow-by forming another thick fluid that sticks to engine surfaces. It is important to know that the chief product of combustion is water vapor. This vapor will combine with the traces of acid causing a reaction with the oil and congeal around carbon particles. This is the chief reason for that sludge caused by driving short trips.The water does not get a chance to boil out of the oil.
 
quote:

Originally posted by Jimbo:
The other type I have seen is soft, mayonnaise-like sludge from moisture.

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.
 
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