I use to own and operated a small single engine airplane, it would sit in the hangar a lot like most other airplanes not flown comercially. I would change the oil and filter every 50 ht=rs and send a oil sample in for testing. I took the airplane out for a flight to warm the oil up for changing one spring cool day, the motor has a oil coller and a thermostat in the line to the oil coller, oil temps. normally rane between 190 F and 210 F, depending on teh outside air temps and how fast I made the airplane climb out on take offs This particular day I flew it for around 20 mintues, oil temps did reach 190 F before landing. I sent the sample in and it came backwith high water content Alos the acid content numbers where higher than normal When water and oil mix you do end up with some acids in the oil I have seen condensation in my valve covers after letting teh car sit for a few weeks with the exhaust evac vacume system hooked up, not seen since I quit using them Lots of gremlins out there