Most common cause is too much short-trip driving. All engines have some "blowby" past the piston rings. Those gases condense in the oil and form sludge. Once the oil becomes hot those hydrocarbons start to vaporize and they get drawn out through the PCV valve to be burned again in the cylinders. That just STARTS to occur when the engine gets hot. From there it takes time for it all to be drawn out.
Also, much of that sludge doesn't drain out with the oil when it's cold. That's why oil is normally changed when it's hot. Keep in mind too that when sludge collects in places like the oil pan it isn't harming anything What can cause problems is when there's so much sludge that it displaces the new oil. Professionals typically do not pour in measured amounts of new oil because, among other variables, it's impossible to memorize the needs of all the different engines. Instead, they will start with about four quarts, then add more as necessary. If there's a half quart of sludge stuck in there, you'll get a half quart less new oil. When those hydrocarbons finally do start to vaporize and circulate with the oil it impedes the oil's ability to isolate moving parts, (lubricate) and that can accelerate engine wear.
Sunday, March 31st, 2013 AT 8:39 AM