Dear Car Talk:
I was taught that when changing the oil, it is best to let your truck sit and let the engine cool, so that all the oil drains down into the pan before you drain it out. But I recently read online that you should let the engine run for about five minutes so that the oil heats up and thins out right before you start an oil change. Which way is best? -- John
Wow. Somewhat accurate information online! I'm stunned.
The five-minute rule is a good one. You warm up the oil so it's less viscous and it flows better. That way, less of the old oil remains inside the engine -- stuck to the walls of the oil pan and other engine parts. Recently circulated oil also picks up more contaminants and holds them in suspension. So you'll remove a little more unwanted gunk when you drain out warm oil.
If you want to be really fanatical about it, John, then you'd want the oil to be fully heated up when you drain it out. In that case, you'd want to drive the car for 15 or 20 minutes and get the engine up to full operating temperature, then pull over and immediately remove the drain plug. Then you'd proceed right to the emergency room after the 300-degree oil ran down your arm, seared a pathway down your right flank and pooled in your underwear.
That's why we strongly recommend against getting so fanatical about changing your engine oil, and why we endorse the five-minute rule for DIY'ers. The difference between changing warm and hot oil is not worth the trip to the emergency room and the permanent disfigurement.
Alternatively, if you've been driving the car and it's hot, let it sit for at least a good half-hour. Or more. This is the equivalent of sitting in the Jiffy Lube waiting room, catching up on Brad and Jen's recent breakup in the 10-year-old People magazines while you wait your turn.
Then put on a pair of gloves, carefully remove the drain plug and get your hand out of the way. And be especially careful when removing the filter. Even "cooled off" oil still can be pretty uncomfortable when it puddles in your Fruit of the Looms, John.