I don't think either the flash point or volatility have much to do with the deposits from the oil. It is not like water spots when you wash your car, or limed up radiators from high mineral water. Fill a radiator with antifreeze and distilled water, and it will never lime up, no matter how long you let it go. You will eventually have corrosion problems when the additives are depleted.
The deposits from the oil are not something that was in the oil you added. They form from a lack of oxidative stability. This relates to inherent properties of the base stock and is fortified by additives. Other additives, including the VI improvers, make things worse. Even the most stable hydrocarbons will burn readily if exposed to flame when hot enough to vaporize enough. It is the less stable material in the oil that oxidizes or breaks down and causes deposits. This is why the less stable it was, and older you let the oil get in the engine, the more deposits you have.
Use good stuff, and change at appropriate intervals, and all of your engine will stay clean.