Hot? oil change
 

Hi all....

Was reading another post and this thought came to me.

That when the engine is hot and you shut it off... the oil drains off the engine parts and into the pan.

Logic would say.. the longer you wanted after running the more oil would be in the pan.

So why toss the oil back up into the engine to get it hot... when its already down below when its cold?

Might take longer to leave the pan.

Don

Sounds Logical. I've heard many times to change it when hot, but never why...

There are 3 reasons that I know of:
1. The motion of the oil circulating into the pump and back thru the drains aids in loosening/disturbing some of the more recently settled depositis sitting in the oil pan, so that they are suspended in the oil and more readily able to be washed out with the oil flow out the drain.
2. Hot oil is thinner, and flows faster & more easily, so it causes the hot sediment in the pan to be thinner and more easily/readily broken up or washed out, almost a solvent effect.
Basically it aids in getting a cleaner change, you can even take it one step further by pouring a bit of fresh oil in with the plug out to rinse the pan. It's not a perfect flush, but it can and does help.

3. The least worrisome and probably least thought about, if you run the engine first, and pump oil to the bearings, it won't drain out and dry up the same as it would overnight. So, when you go to start up, you have a prime of oil in the bearings to help it along for that extended period of time where the new filter element is soaking up fresh oil and taking longer to provide pressure to the engine. Even if you pre prime it, it does help, but still takes a bit longer to pressurize on that first start. Not detrimental to the engine's survival, but it certainly doesn't hurt in extending the engines overall life, and reduces the possiblilty of spinning a dry bearing.

Getting the oil hot makes all the junk become suspended in the oil that would otherwise settle to the bottom of the pan and not get drained out.

After about 10 minutes of being shut off, the bulk majority will have run into the pan anyways but there will still be some left clinging to the parts. That's why we say to drain it hot and let it drain overnight if possible.

It probably doesn't matter. More so since the first owner of the car didn't for the first 25 years and 200k miles.:D

"So why toss the oil back up into the engine to get it hot... when its already down below when its cold?

Might take longer to leave the pan."




Next time you change your oil, wait until the oil stops flowing from the drain and then dump a quart in through the valve cover.

Get down on the floor and see how long it takes for the majority of that quart to vacate the engine.

Now imagine how much quicker it will get to the pan if that oil is hot and 15 centistokes vs ambient and 200 centistokes, as in this "test".

That is a long way of saying that by the time you shut your engine down, get your drain pan underneath the car and pull the plug, the vast majority of the oil that will ever make it to your pan (there is a bunch in the filter and cooler circuit) will already be there.

If you want to change it in 15 minutes.........do it hot.

If you want to change it overnight..........it makes no difference on the oil temperature.

why do you want to toss it back up into the engine to get it hot?
why not change it when you have come home from your errands,
then it is already hot. why waste the fuel having it idle in the drive
way to get warmed back up.
charlie

Yes, as Charmalu says; plan ahead and arrive home with everything already laid out: drain pan, wrench, sheet of cardboard and rags if you like, and so forth. Then you might try this easy experiment: let the hot oil drain out for a few minutes or a half hour and then replace the drain pan with another container and leave it all night to see how much more comes out. Steve