residue on underside of oil cap...any ideas?

[mark71]

yesterday i was changing my oil (castrol 5w20) and i noticed a coffee-with-cream colored residue coating the underside of the oil fill cap.

there wasn't anything unusual about the oil that i drained and there was nothing but normal coolant when i looked under the radiator cap.

any ideas?

 

[96r50]

It's condensation from the crankcase. The engine heats up the oil and the water in it vaporizes and condenses on the coldest parts of the engine after shutdown. It's pretty common in the winter months (there are similar threads in the 80 and 100-series sections right now ). The PCV system will get rid of some of it, but you can also take the truck for a long, spirited drive to boil it off.