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jfryjfry
jfryjfry Reader
12/19/16 2:56 p.m.

I hear and read instructions to warm a vehicle up before changing oil.... I presume it's because warm oil will flow out better than cold. (Read: makes it less viscous)

But I figure an engine that's been sitting at least overnight has as much oil in the pan as it ever will. When I pull the plug I usually let it drain for 30 mins or so while I do other things.

I feel like I'm getting about as much out as is reasonably expected.

Any reason to change my theory?

trucke
trucke Dork
12/19/16 3:08 p.m.
jfryjfry wrote: I hear and read instructions to warm a vehicle up before changing oil.... I presume it's because warm oil will flow out better than cold. (Read: makes it less viscous) But I figure an engine that's been sitting at least overnight has as much oil in the pan as it ever will. When I pull the plug I usually let it drain for 30 mins or so while I do other things. I feel like I'm getting about as much out as is reasonably expected. Any reason to change my theory?

See your first sentence.

Also, oil that has been flowing has picked up particulates that you want out. Particulates will drop out of solution when stagnant.

curtis73
curtis73 PowerDork
12/19/16 3:25 p.m.

Yup. Its like chocolate milk. You always want to shake it before you pour it out so you get more of the chocolatey bits that sink to the bottom.

codrus
codrus SuperDork
12/19/16 3:53 p.m.
trucke wrote: Also, oil that has been flowing has picked up particulates that you want out. Particulates will drop out of solution when stagnant.

Aren't those particulates supposed to be in the filter? Isn't that what it's for?

mad_machine
mad_machine MegaDork
12/19/16 3:54 p.m.

when I worked at a place that didn't care about stuff like this, I would drive to work (about 20 miles) crawl under the car in the parking lot and drain the oil (into a pan) and leave the drain out until lunch time. At that time I would put the plug back in and refill.

rslifkin
rslifkin Dork
12/19/16 3:54 p.m.
codrus wrote:
trucke wrote: Also, oil that has been flowing has picked up particulates that you want out. Particulates will drop out of solution when stagnant.

Aren't those particulates supposed to be in the filter? Isn't that what it's for?

Yes. IMO, most of the benefit of draining while warm is the shorter drain time (and easier cleanup of the drain pan, as warm oil leaves a thinner film and is easier to pour).

Streetwiseguy
Streetwiseguy PowerDork
12/19/16 3:55 p.m.

If you leave the plug out long enough, and its been sitting all night, go ahead and drain. If you have to start the engine to get up on ramps, or something, get it warm.

BlindPirate
BlindPirate New Reader
12/19/16 4:22 p.m.

Some cars where the oil filter is buried behind a bunch of stuff it makes it more pleasant working on a cold engine.

Knurled
Knurled MegaDork
12/19/16 4:38 p.m.

If you have enough "stuff" in the oil that it matters if you stir it up or not, there's hardly any point in changing the oil, the engine needs to come apart.

rustyvw
rustyvw Dork
12/19/16 4:49 p.m.

I have always heard that you should warm it up a little before draining to make sure everything gets stirred up. I don't know if it makes a difference, but I figure it couldn't hurt.

The0retical
The0retical Dork
12/19/16 4:56 p.m.
BlindPirate wrote: Some cars where the oil filter is buried behind a bunch of stuff it makes it more pleasant working on a cold engine.

Having worked on more than one Nissan with the oil filter next to or basically under the collectors... I have come to the conclusion that I don't think it matters much if the oil is warm anymore.

I hear the MR2 is much the same.

Fitzauto
Fitzauto Dork
12/19/16 5:12 p.m.

Due to me not liking hot engine parts near my skin ive always done it cold.

iceracer
iceracer PowerDork
12/19/16 5:16 p.m.

However warm it gets driving up the ramps is good enough for me.

Huckleberry
Huckleberry MegaDork
12/19/16 5:20 p.m.
curtis73 wrote: Yup. Its like chocolate milk. You always want to shake it before you pour it out so you get more of the chocolatey bits that sink to the bottom.

This. You want the tiny bits that pass thru the filter (or bypass it when it's blocked) in suspension in the oil when you drain it.

If you are draining from the lowest point in a conventional oiling system you are probably getting most of it anyway but a dry, semi-dry sump or oil cooler equipped car should have the oil at temperature enough to open any t-stats and flush out the tanks/returns to get all the wee little chocolate into the milk... as well as to make sure the t-stats are open to drain those passageways.

EvanR
EvanR SuperDork
12/19/16 5:41 p.m.

Also, one of the reasons to warm the oil was that it thins out, making it faster to drain.

That might hold weight in the olden days of 30W oil, but I'm betting 0W30 is less viscous cold than hot.

tjbell
tjbell Reader
12/19/16 5:46 p.m.

I've always got my vehicle to operating temp, then let it sit for 15 minutes to let the oil drain to the pan.

Knurled
Knurled MegaDork
12/19/16 5:54 p.m.
Huckleberry wrote:
curtis73 wrote: Yup. Its like chocolate milk. You always want to shake it before you pour it out so you get more of the chocolatey bits that sink to the bottom.

This. You want the tiny bits that pass thru the filter (or bypass it when it's blocked) in suspension in the oil when you drain it.

I would argue that anything small enough to pass through the filter is also small enough to not hurt anything, since it's smaller than any oil clearance in the engine.

I would also argue that, if getting this "fine debris" out is the priority, the worst thing you can do is start the engine and pump it all back up into the head, bore walls, etc.

Mind you, I'm the person who used to leave the RX-7 in gear on the lift, and rotate the engine backwards by turning the driveshaft, to try to slosh the oil out of the rotors...

Knurled
Knurled MegaDork
12/19/16 5:58 p.m.

Another anecdote that might lead to data: I've drained hot oil out of many an engine that was being pulled for an autopsy because it was filling the oil with debris. (Listen to engine - yep sounds bad. Cut open oil filter, yep full of junk...) There's generally a nice, neat layer of crud in the bottom of the pan, being hot didn't get it out of there.

There's also a really primal feeling when you set a still-warm engine on the ground.

dropstep
dropstep Dork
12/19/16 6:06 p.m.

Im pretty sure most people think thr car needs to be 200+ too change the oil because of old logic. Im no expert but i drain my wagon cold and let it drain for 2hrs or so. Ive donated enough skin too hot exhaust on gm's E36 M3ty 3.6

rslifkin
rslifkin Dork
12/19/16 6:43 p.m.
EvanR wrote: That might hold weight in the olden days of 30W oil, but I'm betting 0W30 is less viscous cold than hot.

Nope, 0W30 is still much thicker when cold than when hot. Of course, a straight 30 of the same thickness when hot will be even thicker when cold (than the 0W30).

hhaase
hhaase Reader
12/19/16 7:14 p.m.
The0retical wrote:
BlindPirate wrote: Some cars where the oil filter is buried behind a bunch of stuff it makes it more pleasant working on a cold engine.

Having worked on more than one Nissan with the oil filter next to or basically under the collectors... I have come to the conclusion that I don't think it matters much if the oil is warm anymore.

I hear the MR2 is much the same.

My MR2 is much easier to do an oil change. Drive it around, wait till it's warm, all the oil has now leaked out so just re-fill and you're done.

former520
former520 Reader
12/19/16 7:38 p.m.

I know of an old method that borders the cold/ hot line and helps flush as well. You need a helper to do this, but it is the best.

Get the car up in the air and hot. You need one person below and one above. The person above needs to have at least a gallon of fresh oil ready and funnel in fill hole.

The person below needs be ready to remove and reinstall the plug.

When everyone is in position, with the car running, pull the plug and start to refill at the same time. Keep doing this until the fresh oil is coming out and has cleared the engine of the old oil. It may take 2 gallons. Once it is coming out clear, shut down the motor and put in the plug to keep as much of the oil in as possible. Now you can remove the filter, install the new one and top off to spec knowing you have flushed all of the old stuff out.

spitfirebill
spitfirebill UltimaDork
12/19/16 7:57 p.m.

I like to change it as hot as I can.

Gearheadotaku
Gearheadotaku PowerDork
12/19/16 8:12 p.m.

"cold" and "hot" are somewhat relative here. "cold" oil on a 90 degree day will flow way better than 'cold' oil on a 10 degree day.

if you are changing your oil at the right interval with quality products I don't think there is much difference.

Nick (Bo) Comstock
Nick (Bo) Comstock UltimaDork
12/19/16 8:17 p.m.

I usually get them warm but not hot. I've changed them cold too. I don't really think it matters too much. I always use the quart that was left over from the last oil change to flush through though.

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