Dear Tom and Ray:
I always change my own oil on my cars. I let the car sit overnight and change the engine oil the next day. My daughter said that it would be better to change the oil when the engine is hot, like when I get home from work. So ... which is the preferred method? -- Will
RAY: Your daughter's right, Will. The reason we change the oil when it's warm is because it flows better and comes out faster.
TOM: It's not a big deal. But when the oil is cold, it's more viscous (it's thicker), so it drains out more slowly. And even if you're willing to wait longer for it to drain out, it's likely that a bit more oil will remain coated on the inside walls of the engine when you're done. Not a lot more than if the oil was warm, but a little more.
RAY: So I'd say a warm oil change is a little bit better.
TOM: Now, there is one major disadvantage to a hot-engine oil change: It hurts! First of all, when you remove the drain plug, if you don't know what you're doing, hot oil can run down your arms. And it's not as pleasurable as the room-temperature arm grease you get from eating one of those delicious In-N-Out (of the cardiac unit) burgers.
RAY: A lot of today's cars also have oil filters that are really buried and hard to reach. So the chances of burning yourself while trying to unscrew one of those is quite high.
TOM: So, for that reason, here's what we recommend. First, don't do the oil change when the engine is red-hot. Let it sit for half an hour or an hour before starting your work. The oil will still be warm enough to flow easily, but the exhaust manifold won't be glowing red and 800 degrees.
RAY: Second, wear a protective glove, like a welder's glove or a large kitchen mitt (they make some with fingers) to protect your hands and forearms.
TOM: Or just change the oil when the engine is cold. You'll have to wait a little longer for it to drain if you want to get most of the oil out. And a small amount will be left behind. But you'll still get 98 percent of the benefit of the oil change. And you'll be able to keep all of your arm hair.
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BringBack914
A friend / mechanic once told me that it's also better to do it soon after shutting off the engine because all the debris in there will be suspended in the oil. If you let it sit overnight everything will settle to the bottom of your oil pan and just get dredged up again the next time you crank it up.
charlieputt
So, with that in mind, drain the oil immediately after shutting down the car, and then just give it a half hour or so to drain while the exhaust cools down before going after the filter. I always give my car plenty of drain time.