Conventional wisdom as told to me long ago is change oil when it is warm, after driving because it suspends the "bad stuff" in the oil and it comes out when you pull the plug. My thinking is that by letting the car sit overnight, more oil drains from the upper engine down to the oil pan and whatever "bad stuff" comes with it and sinks to the bottom if it is heavier than oil or is on the top if it is lighter. But when you pull the drain plug it all comes out. And of course it is the filter's job to catch a lot of it anyway so changing the filter gets rid of bad stuff. So why change when it warm? Is the wisdom different for fossil and synthetic oils?