I don't think it makes much diff. If the metal of the engine is hot I think the oil will flow out faster and more completey. Quote: why do all info. on changing oil says to run the engine for 5 minutes.... end of quote. Not all places say do it hot. I also do not think any particles should be in the oil, hot or cold as that is what a filer is for. You may be correct in that it is old school as they say.