About 4 months ago I bought a 2001 GMC Savana box truck (4.3 V6).  The only things I noticed that seemed out of the ordinary was an intermittent "ticking" sound, and that it seemed to run cool, about 150 or so...but for all I know that temp could be normal.  I've driven it for a few thousand miles with no issues.  Anyway, did my first oil change and the oil came out fairly thin and an unusual light chocolate color, and the filter was almost packed to the brim with globs of black sludge.  I've been told the color suggests a coolant mix, but I'm not 100% sure.  Here is some random information that may or may not be helpful.  Spark plugs looked good, with just a barely noticeable amount of an oily substance.  Little bit of condensation/smoke out the tailpipe but doesn't seem like an abnormal amount.  Rented a block test kit and, assuming I did it correctly, didn't show the presence of exhaust gases in the cooling system.  Coolant in reservoir clean, coolant in radiator looked very slightly murky but no oil slick on top.  Thanks a lot for any help/leads.  ~J.

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My assessment would be that the cold temperatures (it should run about 210) are the cause - that engine is seriously sludged up and the oil pickup screen is likely to be clogged.

Engines make a gallon of water for every gallon of fuel they burn, and while most of that goes out the tail pipe, some of it goes past the rings into the crankcase with the inevitable blow-by.  If the engine is running too cool (and that one definitely is!), the water in the blow-by tends to condense and mix with the oil and form sludge.  On an engine that is running the correct temperature, the PCV system eliminates the water as vapor.

That's what you have, and a bad thermostat is the root cause.  Regularly driving a vehicle very short distances (less than a mile) or regularly running it briefly without letting it warm up will cause problems like the one you have as well.

Usually a dealership will replace a sludged up engine because de-sludging one and repairing the resulting damage (depending on how long it has run cold and how badly it is sludged) is more expensive than replacing the engine with a long block.

That's  a raw deal.

Good luck!~

Richard

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