Humm....I always thought that the "vapor" from a warm engine was water vapor. So it is a good thing to let it out. When I did the first oil change after a 15 year slumber. And about 500 miles of good running. Imagine my surprise when I found about a 1/2 cup of clear water in the bottom of the filter canister. When I did the next oil change I found no water in the system any where. No water leaks and no changes to the truck in that time. Makes me glad I have that big old canister filter. Let it steam let it steam. Oh yeah, I use a 180 thermostat. Modern engines are closed up real tight. To prevent evil stuff from getting into the air. So, where do you think that stuff goes? Into the oil of course. No place else for it to go. That is why you have to change oil every 3000 miles or 3 months. Now that is some nasty oil.
