T18skyguy wrote:
This is what I've read on the longevity of oil in the pan by date. The oil slowly combines with oxygen, and results in oxidation, which leads to sludge/coke or whatever other bad things. The filter media can also be attacked and ruined by the acids in oil while it sits in the filter. Then there is also the steady addition of water to the oil. This happens even when the engine is not running. The air in the engine is the same as outside, so when it hits the dew point, it condenses inside the engine, makes rust if it can, then settles into the pan. That water burns off if you run it, but not if it's parked for long periods. At night the engine inhales when the air gets cool(contraction), and when the day warms up it exhales(expansion), kinda like we do. I do the Mobil 1 annual oil once a year.
Right answer, finally! The moisture and acids that build up in the oil will slowly corrode the internal components of the engine. Its not that the oil breaks down, it doesn't; its the impurities that build up in oil that has some miles on it.
