Changing the oil when hot is normal procedure but not required. The thinking is when it's hot, the sludge and other debris that is being carried to the filter is suspended in the oil that is draining out, and you want to get that stuff out. When you wait for the oil to cool down, some of that debris might settle out and not come out with the oil that not flowing so freely. On the other hand, there is always a lot of old oil that doesn't drain out. It's stuck in passages and the oil pump. The longer you wait for the oil to cool down, the more of that oil has a chance to drip into the pan and get drained out.
Keep in mind that when you go to one of the "speedy lube" shops, they don't have time to wait a couple of hours for the oil to cool down. They have to work fast to avoid burning their hands on that hot oil. Also, there are a real lot of customers who are willing to pay more for the fast service, but they will scream and whine if the job takes five minutes more than expected.
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Friday, December 14th, 2018 AT 3:32 PM