Oil changes: Warm or Cold?

[CobyRupert]

When the engine is shut down the hot oil is going to drain into the sump so if you drain it cold it doesn稚 need to drain off engine parts except the oil pump inlet. If drained hot almost all the oil will drain off the parts. Worst is slightly warmed and then drained because gunk can stick to the engine parts. But with today痴 oils it probably doesn稚 make much difference. I remember the old days when the oil we drained started coming out in globs near the end, and that was with 1,000 or 2,000 mile changes on cars and pickups, 50 hour on tractors.

Does/did it really come out in globs, or does it just look that way once the level is low enough that air can go IN the oil plug hole? A case of the viscosity of oil making this air "gulp" look like globs of oil are coming out?

I think a factor in the hot/cold "debate" (there really is none, but playing :devil: ); is how does oil flow out of the drain hole? Doesn't it flow off the bottom? (Significantly enough to carry particles off the bottom?) Is there "sludge" oil on bottom with a different viscosity than rest of oil pan, and does it flow differently/stay behind when plug is removed?

 

[cat fever]

I always change on the hot side.

I usually run the engine until the filter is hot to the touch, shut off the engine and drain the oil/change filter.

That works best for me on both the tractor and truck. :2cents:

 

[Ford850]

Has anyone had gunk come out during an oil change recently? With modern oils and better filters, I don't understand how getting an engine hot can suspend 'stuff' but not have it get caught in a filter. I changed the oil in my 60 year old Ford 850 last week, and since it has a huge drain plug (2" or so) I curled my finger up inside to rub the bottom of the pan after the old oil was drained. It was squeaky clean. Well, not quite squeaky since it did have a light layer of oil, but there was no gunk, sludge, or particles of anything.

When the weather is cold like it is now, I prefer to get an engine hot but let it cool down and change when the oil is warm. That allows the oil to drain back down but still flow easy when draining. In the summer when the oil is relatively warm, I change it without pre-warming.

 

[CobyRupert]

I run the engine under full load until operating temperature is reached. Then I shut the engine down and monitor the temperature of the oil in the pan with an RTD probe until the temperature is at 135 degrees F and then pull the plug. This method allows for the maximum suspension of particulates while preventing contact burns from hot oil as it is below 140 degrees at the time of draining.

RTD probe eh?? Hmmm...
Yep, probably best if I take the oil pan and valve covers off and power wash everything with a sludge remover as long as I'm changing the oil.

At least your posts come with a "**WARNING:..."

 

[mcfarmall]

Coby, I think you may have sensed my sarcasm WITHOUT a warning!

 

[3Lfarms]

I think the hot/cold thing is mostly a leftover from the past when oils and filters were poor.
The owners manual for my 24 Dodge says to change the oil every 500 miles and drop the oil pan to scrape out the sludge and clean it with kerosene once a year. The car doesn’t even have an oil filter.
I just run cheap Walmart 10-40 in it and change it every couple years (100 miles or so total). After 25 years of that, I dropped the pan to clean it a couple years ago and it was still spotless inside.
Today’s lubricants are infinitely better than they were back in those days.

 

[LouNY]

This has been an enjoyable read especially a couple of the later ones,
I prefer to change mine when it has been warmed up.

I'll ask another question in this vein, after you have let your engine drain well, and completed your
change do you just start it up and watch that red light till it goes out or the gauge comes up, OR
do you disable the ignition or fuel shutoff and crank the engine over to get oil back up into all the passages
you just drained it from???

For what it's worth RAM on the eco-diesels now wants a half hour draining time.

 

[ArlyA]

A warmer engine will simply speed things up. Why not do it flows out quicker??

 

[fxdb96]

Would the oil flow better cold with multi-viscosity oil that are in most engines? As the oil heats it becomes thicker. Don't think it it really matters.

Dave

Dave,

Great point I agree!

 

[TractorGuy]

I always do mine cold but after the engine was worked before parking. I assume the oil filter has done it's job and parking it after working should have ALL the oil drained into the pan. I don't care how fast it drains. I pull the plug and go about some other task while it drains. Don't care a thing about having hot oil splash on me.

 

[mcfarmall]

Here's another thought for the lubricologists: Aren't multi viscosity oils designed, for example 5w-30, to have the viscosity of a SAE 5 at LOW temperatures and the viscosity of SAE 30 at HIGH temperatures? That was the whole point of a multi viscosity oil, so you wouldn't have to switch viscosities seasonally...a 5w in the winter and a 30w in the summer. So theoretically, you would want to drain cold, as the oil would behave like a SAE 5 which would flow better and get all the nasties out of the oil pan.

The ideas and thoughts shown above are NOT sarcastic in nature but actual discussion points not meant to invoke feelings of humor.

 

[Looking4new]

I change my oil hot. It is the way that I was taught.

 

[Ford850]

Multi viscosity oils do not get thicker as they warm up. They 'thin' at a slower rate as the oil temperature rises, and thicken slower as the temperature drops. A 5w40 flows like cold 5 weight oil when cold, and flows like hot 40 weight oil when hot. Hot 40W oil flows better than a cold 5W oil, so hot 5W40 flows better than cold 5W40.

 

[Spindifferent]

Politics, religion, oil change interval, synthetic vs conventional, and now warm vs cold. To each their own, I say.

 

[ArlyA]

So a warm engines used oil will flow out quicker when changed and maybe carry more debris out with itself. I'll stick with warm oil changes, politics and religion notwithstanding.

Multi viscosity oils do not get thicker as they warm up. They 'thin' at a slower rate as the oil temperature rises, and thicken slower as the temperature drops. A 5w40 flows like cold 5 weight oil when cold, and flows like hot 40 weight oil when hot. Hot 40W oil flows better than a cold 5W oil, so hot 5W40 flows better than cold 5W40.

 

[CobyRupert]

A warmer engine will simply speed things up. Why not do it (so it) flows out quicker??

because...:
I'm impatient and want to change oil now, even though I haven't used tractor. So this means an unnecessary cold start (the wear and tear of this is not a big deal), but this time of year it means plugging tractor's block heater for an hour or two, and maybe even having to hook up a battery charger for an hour or two (or use boost mode etc...)

Yes, oil FLOWS out quicker, but you've spread it around the engine and hot oil will still take awhile (longer?) to drain down to the oil pan as completely as an un-started engine with cold oil. (When I change hot oil and then dump the oil catch-pan into a pail, there's always some left in the pan. Only when I leave the pan tipped up for a couple days does it completely drain.)

- So hot or cold, I guess how long does one leave the oil plug out is another separate question?

Here's another question to ponder: Does colder (more viscous) oil falling out the drain hole, "pull" more oil with it than warm (less viscous) oil?
(That is, does a more viscous fluid leave less droplets behind?)

 

[CincyFlyer]

"Hot" is the only correct answer. Every piece of equipment I've ever owned says to warm up the engine. Every Japanese auto and motorcycle manufacturer says to do so. Mahindra says to do so. More "stuff" is suspended in the oil, and the thinner oil has a higher "exit velocity". I pull the plug as soon as I stop the engine, then I work on the filter. I clean/replace air filter and other items. I don't put the plug in until there is essentially no more coming out of the sump or oil pan.
Reductio ad absurbum: At 0°F, you'll never get all of the old oil out in a reasonable time. Any stuff that's settled may stay in the pan. Nothing to lose, everything to gain, by changing hot.

 

[deserteagle71]

"Hot" is the only correct answer. Every piece of equipment I've ever owned says to warm up the engine. Every Japanese auto and motorcycle manufacturer says to do so. Mahindra says to do so. More "stuff" is suspended in the oil, and the thinner oil has a higher "exit velocity". I pull the plug as soon as I stop the engine, then I work on the filter. I clean/replace air filter and other items. I don't put the plug in until there is essentially no more coming out of the sump or oil pan.
Reductio ad absurbum: At 0°F, you'll never get all of the old oil out in a reasonable time. Any stuff that's settled may stay in the pan. Nothing to lose, everything to gain, by changing hot.

Thank you!

People seem to forget that there's more than just minute metal particles in that used oil. The oil filter takes care of those. Its the "products of combustion" - the acids, soot, water, etc. (even unburned fuel that's made its way past the rings) that need to be thoroughly dispersed and dissolved in the engine oil before the oil is changed and the only way to do that is by running the engine until it is good and hot.

 

[Oldoak]

The best way is the one that make's you feel best.:confused3:

That would apply to many topics here on TBN.

Politics, religion, oil change interval, synthetic vs conventional, and now warm vs cold. To each their own, I say.

:thumbsup:

 

[CobyRupert]

Thank you!

People seem to forget that there's more than just minute metal particles in that used oil. The oil filter takes care of those. Its the "products of combustion" - the acids, soot, water, etc. (even unburned fuel that's made its way past the rings) that need to be thoroughly dispersed and dissolved in the engine oil before the oil is changed and the only way to do that is by running the engine until it is good and hot.

Good point!
....but where are they before you start the engine? Either on the bottom or floating on the top?