Oil Change on a Cold Engine

[blupupher]

Originally Posted By: znode
The ability of any solvent to dissolve solute is going to be dependent upon temperature.

The hotter the oil is, the more muck you will remove, period.

The "muck" will be dissolved the same hot or cold (so long as we are not talking below freezing temps).

I always do it cold if possible, less chance of me burning myself.
More time for all the oil to drain into the pan and get as much out as possible.

 

[PolarisX]

I always do them hot. Oil flows faster, filter comes off easier.

..And it's over with before I have the change to have to start something else.

 

[BrocLuno]

I do cold changes all the time. Jack the vehicle so the pan plug is lowest point, pull plug, let drain, go do something else. An hour later it's done. Put in oil. Run motor make sure you have pressure. Good to go.

Next week, change filter so you have some overlap on "made in engine" AW compounds. All good

 

[Nyogtha]

I've done the vast majority of my oil changes at ambient temperature. I don't like being underneath a vehicle with warm components, let alone hot ones. I did a bunch of ambient oil changes with sraight SAE 30 in the 70's & 80's with never a problem draining.

I put the vehicle up on ramps the night before typically. Oil filter gets changed after the oil pan finishes draining, then refill with fresh oil.

 

[barryh]

I use a vacuum extractor these days and the oil needs to be at least warm to get it out in a reasonable time.

 

[mjoekingz28]

I have seen threads come apart by pulling hot drain plugs so I have been doing cold for about five years now.


I didn't think I had overtorqued the prior oil change so I don't know why the pan or plug would strip.


This had me wondering how lube shacks got by. They change HOT HOT oil all summer long with minimal cool down.

 

[meborder]

Some of you don't know much about chemistry. Which is fine, but ought not be giving advice about thing which you don't understand.

As temperature goes up, solubility increases also. As the temperature falls, solubility decreases. So, if the solvent contains more "stuff" at a higher temp than what it can hold at a lower temp, then "stuff" will precipitate or fall out of solution as the temperature drops.

There is an exception to the rule, of course. Of you dissolve a huge amount of a solute at a very high temp then very slowly cool it down, you can keep it in suspension creating what is called a "super-saturated solution"

https://m.youtube.com/watch?v=1y3bKIOkcmk

However, outside of these special conditions, precipitation will occur and leave "muck" at the bottom.

So, in a really dirty engine, changing your oil hot is best because the contaminants will stay suspended in the hot oil, where if left to cool down they will fall out of suspension and may not come out.

In a clean engine it wont much matter.

 

[demarpaint]

I was taught to change the oil after the car has been driven. That stuck with me, and I continue to do so. I wear gloves because I don't like cleaning oil off my hands and they protect against heat.

 

[JoelB]

If there is muck in the pan why not just drop it and scrape it all out? MMO won't clean it out for you.

 

[kohnen]

Before I retired, I had a 33 mile commute one way. When it was time for an oil change, I'd come home Friday evening, jack up one side of the car, slide an oil pan under there, and remove the oil plug and the oil filter. Jacking the car up tilted the oil pan making the drain plug the absolutely lowest part of the pan.

Then, I put the jug of new oil and filter on the floor of the driver's position (just to remind me not to drive off).

Saturday morning, I'd complete the job.

I think this method got as much of the old oil out as practical.

 

[BrocLuno]

And since the plug was lowest, the "muck" would settle out the plug too

 

[CR94]

Originally Posted By: Colt45ws
I do it warm after it has cooled for awhile. I burn myself all the time on hot oil changes. I dont particularly feel the need to do the same on my own stuff.
I did a variation of that with the Mazda, from which the oil came out hot enough to burn in summer. Solution to get thorough draining with less risk of burns:

1) Let it cool a half-hour or so;
2) Move car to oil-change spot, leaving engine idling;
3) Loosen drain plug, position drain pan;
4) Rev engine briefly to stir up anything loose;
5) Turn off ignition;
6) Finish removing the loosened plug;
7) Wait until dripping near stops before replacing plug.

With the Prius, positioning the car and accessing the drain plug are both so much more cumbersome and time-consuming that Step #1 (cool-down) is superfluous, especially since it's reluctant to idle.

 

[Shannow]

Originally Posted By: meborder
Some of you don't know much about chemistry. Which is fine, but ought not be giving advice about thing which you don't understand.

As temperature goes up, solubility increases also. As the temperature falls, solubility decreases. So, if the solvent contains more "stuff" at a higher temp than what it can hold at a lower temp, then "stuff" will precipitate or fall out of solution as the temperature drops.

There is an exception to the rule, of course. Of you dissolve a huge amount of a solute at a very high temp then very slowly cool it down, you can keep it in suspension creating what is called a "super-saturated solution"

https://m.youtube.com/watch?v=1y3bKIOkcmk

However, outside of these special conditions, precipitation will occur and leave "muck" at the bottom.

So, in a really dirty engine, changing your oil hot is best because the contaminants will stay suspended in the hot oil, where if left to cool down they will fall out of suspension and may not come out.

In a clean engine it wont much matter.


Spot on...

and for those who (because it sounds good, not because they ACTUALLY KNOW) reckon that "the muck" is equally soluble in cold or hot oil, here's a video on the temperature solubility of varnish.



That's Celsius...60-65C is usually to point at which people can still (just) hold onto stuff like drain plugs.

If you do it cold in the morning, the new oil will have to pick up immediately the "muck" that was settled out and not dissolved.

 

[CT8]

It is better to change the oil hot but it is best to change the oil. Do what is the most convenient for you.Just change the fluids because clean oil is happy oil.

 

[bbhero]

Great job guys. Explanation by meborder was very well done. And thanks Shannow for the video. You guys are a tremendous asset on here. Rock on!

 

[theeagleflies]

Gee Wiz; I am 60 and never heard of a cold oil change. I was taught not to do that actually.

FWIW Everything that was suspended in the oil has settled and stuck to oil pan when cold. Most of that junk would flow out with hot oil after a drive. That is what the auto techs were taught when I was growing up and started to get into cars. Drive the car 1st, to get the oil up to operating temp, let cool for 15 or 20 mins and then drain.

Different strokes I guess.......

 

[hatt]

I change mine hot after a good drive. You can look in the bottom of the jug you pour used oil into and see plenty of gunk. I have no idea how long this stuff takes to settle out but I assume the larger(and likely more damaging) particles fall out first. I do know changing it hot gives me the best chance to get this stuff out. And maybe the fast stream helps pull out anything on the bottom of the pan.

 

[B320i]

I've seen the cold oil change idea from a popular Australian YouTube mechanic. The theory there being that all the contaminants would be in the oil pan, rather than stirred up. Evidently, that isn't perhaps the case.

Out of curiosity though, I wonder if leaving some of those contaminants behind would help the new oil's anti-wear package develop (as has been suggested in other threads - not changing oil & filter at the same time so as to reduce wear)?

 

[SteveSRT8]

Originally Posted By: hatt
I change mine hot after a good drive. You can look in the bottom of the jug you pour used oil into and see plenty of gunk. I have no idea how long this stuff takes to settle out but I assume the larger(and likely more damaging) particles fall out first. I do know changing it hot gives me the best chance to get this stuff out. And maybe the fast stream helps pull out anything on the bottom of the pan.


Precisely. I have postulated about slow draining being an issue in certain engines with aftermarket drain valves installed. Some of them are markedly smaller than factory drain holes and thus seem to encourage a slower, less flushing drain. I have actually observed this in our trucks where Fumoto was used for many years.

Another great reason for a hot oil change is your engine will have residual lubrication to protect it during a dry start with an empty oil filter...

 

[SR5]

Originally Posted By: meborder

As temperature goes up, solubility increases also. As the temperature falls, solubility decreases. So, if the solvent contains more "stuff" at a higher temp than what it can hold at a lower temp, then "stuff" will precipitate or fall out of solution as the temperature drops.
....
In a clean engine it wont much matter.


Good chemistry mate, thanks for taking the time.

You sometimes see people posting pictures of inside the valve covers with a varnish pattern. Some areas are clean while others have varnish. Sure oil access / splash is one parameter, but often to me the varnish pattern reflects the hot and cold parts of the engine cover, where the cold parts have the varnish. The hot oil lands on a cooler (but still warm) part of the engine cover, the oil cools a little and the varnish drops out of solution.

But I also agree, it's probably not a big deal in a clean engine and a well looked after car, which would be most BITOG members.