Oil fill cap/temperature question

[JoeP]

Back in The Day, I worked a Summer for Mobil in their engine testing lab.  Foam or jelly in the cooler parts of the engine can occur during the winter if you do not get the engine to full operating temperature for 20 minutes or so.  It is a common problem for people who only use their cars to go to the train station.

Water condenses in every engine when it gets cold and mixes physically (not chemically) with oil on the upper parts of the engine.  Extended operation boils the water away, and no damage occurs.    This usually is not a significant problem in the sump that supplies the oil pump.

However, upper-engine gunk can build up after repeated short starts in very cold weather.  It can cause long term trouble if foam progresses to the point where it mixes with crankcase oil and water gets pumped into the bearings. 

Oh, if the foam/jelly smells sweet or looks yellow, the water could be coming from a coolant leak in a water cooled engine.  Look for oil in the radiator.