Why not change oil when cold?

[TheBrian]

I've always been told, when you're changing oil, you do it with the oil hot. Not so hot that it burns you, but as hot as possible so it drains down into the oil pan better.

 

Why don't we change our oil first thing in the morning, when it's had all night to drain into the oil pan?

 

I'm going to try out synthetic, so I'm interested in getting as much of the old oil as possible out this time.

[Al_SemC]

I've always been told, when you're changing oil, you do it with the oil hot. Not so hot that it burns you, but as hot as possible so it drains down into the oil pan better.

 

Why don't we change our oil first thing in the morning, when it's had all night to drain into the oil pan?

 

I'm going to try out synthetic, so I'm interested in getting as much of the old oil as possible out this time.

 

Because you don't just want to get oil oil out; you want to get sludge out too. That stuff basically doesn't flow unless it's hot-ish. While you do have a point about the oil being all stuck up inside the engine after you run it to warm it up, I'd rather have a little old oil kicking around in there then a big glob of sludge that might think it's cool one day to come loose and lodge itself in my oil pickup.

 

If you're really that worried about it, warm the engine up, set it to drain, then go have lunch or something. An hour should be sufficient to get all but the last dregs of old oil and sludge out. I find that I get most of it out each time and I usually let it drain about half an hour.

[Gnuman]

Warm oil flows better (it being thinner and all), so more of it comes out in a given amount of time. If you want to let it sit all night, that is fine, but I recomend that you start with it warm to begin with, so more of it flows into the drain pan. You will not get it all out in any case. The best you can aim for (unless you plan on taking the engine apart and hand cleaning every part) is to get 99.8% of it in two oil changes. . . Having a bit of dino oil in the crankcase when you go to synthetic will not harm anything in any case. Yo just loose 0.5% of the extra protection. . .

[nipper]

Changing the oil while cold you will never get all the old out of the car. Oil is thick when cold, and colder it is the thicker, leaving more old contaminated oil behind. Also instead of making it a 15 minutes job, it can now become an hour or so wating for the oil to stop driping.

 

 

nipper

[Setright]

Why not when cold? I have often wondered a bit too.

 

It's true that more oil would be in the pan when cold, but I think that warm oil would carry out more sludge/particles because it would be in suspension.

 

The particles of soot and ash that may be present in the oil would tend to sink to the bottom of the oil pan overnight and not get drained out.

[Tiny Clark]

If you were to change it in the morning, all the oil would be in the pan, but it would be thick and stick to the sides of the pan.

 

If it's warm, the oil is thin, but there will still be oil in the engine that hasn't made its way to the pan.

 

Ever pour a new bottle of oil in a car, set it set upside down for a minute or so to drain in, then set it off to the side for a day? You'll see a fairly decent layer of oil in the bottom of the container.

 

It's a lose-lose situation...

 

Maybe if you heated the oil pan up with a good heat source in the morning, you'd get a majority of the old oil out.

 

The win-win situation is to change your oil regularly, and not worry about yourself about such a little problem. Worry about beer and wine taxes instead, if you must!

[Dr Subenstien]

The biggest reason i think to do it while it is hot is that it also gets more of the contaminates out. When the engine is hot verythiing is mixed up and all the dirt is suspended in the oil and obviously it also drains better warm.

 

When the oil is cold not only is it thicker but all the dirt is settled out and more if it will remain on the bottom of the pan until it gets mixed up again by the running engine in your new oil. the filter does not filter everything out.

 

my 0.02cents

[TheBrian]

If you're really that worried about it, warm the engine up, set it to drain, then go have lunch or something.

Whoever says you can't have it both ways just isn't thinking hard enough. Good thinking, Al.

 

The problem with every theory presented here except TinyClark's is that you all say the oil has to be hot to flow out of the engine, carrying gunk with it. Well, it is, in fact, hot, when it begins to drain into the oil pan when I shut the car off at night. It carries contaminants and gunk down into the oil pan. So I guess the reason to drain the oil while it's hot is so as to have a hot oil pan.

 

I pulled the drain plug at the beginning of my lunch hour. 40 minutes later, it was still dripping, with one drip every several seconds. I went back to work with the oil catch pan under the car. Six hours later, it was *still* dripping, though only one drip every few minutes. This is 10w30 at about 3oC.

 

Note, a good reason to change the oil when it's hot is that you'd much rather have 35oC oil on your fingers than 0oC oil.