I saw this in another thread. It scared the beejeesus out of me. How does water wind up getting in there in the first place???
Humidity from the air.
Ever notice condensation form on the outside of a cold drink? That water condensed out of the humidity that was in the atmosphere. Cold air cannot suspend as much water within it as hot air.
Every time your engine cools down, the crankcase, which is vented to the atmosphere, precipitate condensation on the interior walls and dribble down until the sump. The more cool down cycles and the higher the humidity in the air the faster the water collects inside the engine.
To combat the water build up, the engine must attain a temperature which allows the water to evaporate back into the atmosphere, and hold that temperature until all the water inside has gone. An oil cooler without a thermostat is totally reliant on the outside temps and the run times of the engine to rid itself of internal water. Even with a thermostat to shunt the oil around the cooler, the oil within the cooler can trap water that never gets circulated or heated enough to shed its water content.
Further, oil has an optimum temperature range for proper lubrication of the internal parts. Too cold is almost as bad as too hot.
Thermostats, help out the the "too cold" only if the engine is run long enough or hot enough for the oil to achieve operating temp.
The oil type does not affect the formation of water inside the engine. The viscosity of the oil does have a roll in and during the warm up time of the engine.
Cheers,
