I've read several threads that talk about changing oil shortly after a car has been driven a while. Why is this? Is there any harm in changing oil when the car has sat for a few hours, or even overnight? It seems to me that if a car were just run it would be too hot under there especially if hot oil shot out all over your hands. How long does the engine need to run before changing oil - 10 miles, 20 miles or what? Maybe the oil needs to circulate a bit if you are changing it in below freezing weather but is there any harm in parking your car at night and changing the oil in the morning if the temps are moderate? It also seems to make sense to me that the oil would sort of "settle" in the pan overnight and the change would be more efficient but I just don't know the mechanics of oil "circulation" enough to be sure about that. The reason I ask is that I will change my oil/filter this weekend (first time I've done my own change in over 20 years) and would rather try it cold so as to not scald myself if I make a mistake.