Emulsified oil in the dipstick tube is very common regardless of the type of cooling system. As an engine warms up and the lube oil temps rise, the moisture in an engine crankcase vaporizes and accumulates in the coolest spots which the dipstick tube happens to be one of and easily noticed. On a hot engine, if I remember, I remove the dipstick, wipe it dry and leave it on the machine seat so I see it and reinstall it before the next start. The heat in the engine will dry out the moisture from the dipstick tube. The engine crankcase breather system is another place for moisture accumulation, but never noticed unless the system is disassembled and looked at. The interior of valve covers on some engines is another place where moisture accumulates.
One of my former high mileage trucks had a very long engine oil dipstick tube and dipstick. The metal dipstick tube interior and dipstick would get rusty on the upper portions of both. One of my drivers snapped the dipstick in the rusty area as he was checking the oil at a truckstop on the west coast, fortunately the truckstop engine service dept had one in stock and was able to fish out the broken part. Some large engines have a moisture separating crankcase breather system.
Mad Mackie in CT:smile::biggrin::laughing:
