Originally Posted By: solorexpy
Ok, correct me if I'm wrong, but doesn't the heavy metals and other undesirables sort of settle on the bottom of the oil pan and pulling the plug helps to get rid of said undesirables? Pumping doesn't seem like a good idea, at least to me.
Not sure that's really the case. Alas, I can't provide hard evidence either against or to confirm what you stated.
The way I see it, you've got two types of particle/crud in the engine. The first type is so small that it just gets suspended in the oil and thus comes out with the oil when you extract it. The second type are larger particles that cannot be suspended in the oil but instead get trapped by the filter media.
There shouldn't be anything settling at the bottom of the oil pan. But even if there is, if it's a soft settlement, it'll get thrown back into circulation when you run the engine and heat up the oil, and it's always a good idea to extract the oil while hot. On the other hand, if it's some hard baked on settlement that won't budge, then it will probably not come out on its own through the drain plug either.
As for the whole discussion regarding how much can be extracted vs. how much can be drained, it is really oil pan design dependent. If the engine was designed with oil extraction in mind, you can extract it all. People have done experiments when they extracted first, then unscrewed the drain plug and nothing else came out. But if your oil pan has a weird shape where the extraction tube can't reach all the way to the bottom, then you should probably stick with the traditional drain plug method.
