Engine temp before oil change?

[ABN_CBT_ENGR]

What's the difference between starting your car in the morning after it sat all night or cut multiple days and starting your car after an oil change? All the oil that was going to drain back into the pan from the upper engine has drained back so there is no difference between oil film after an oc and after sitting overnight. The pan is full after an oc and after sitting all night. Therefore the difference must be with the oil pump. The pump is empty and needs to get primed after an oc. It takes 3-5 seconds to get the oil pump primed and oil flowing to the engine?

The truth is a lot of both "false data" (studies promoting anecdotal views rather than fact and being generally "accepted" on the basis of ineffective challenge rather than affirmative proof) combined with the fact that there was a point in history with primitive oils combined with different machine technology where it was "more true" than less untrue but the legend continues.

Like millions of others, I was brought up and taught the conventional wisdom and later had to see it proven inaccurate (notice that "wrong" is not the correct description to use because it was "right") before I would accept it so I generally don't flag on the topic.

With the baseline acknowledgement that neither machining, tribology or design is "perfect" so there is no possible scenario where 'start up wear' can be eliminated......

In days of old- there was most certainly a lubrication starvation issue on many fronts- different chemistry, metallurgy, clearances, finishes and other requirements.

Today, nowhere near as much ( but still present) but the damage and end effect potential has been reduced to what could be viewed as statistically insignificant ( assuming a good oil with an accepted change practice)

Assuming a properly built engine and an adequate lubricant starting cold ( cold being defined as all chemistry and metallurgy not being at design thermal limits irrespective of ambient temp)

There will be a percentage of oil in the system from the last operation, there will be some free air/void and all clearances will be fully open.

Starting there- a brief ( less than a full second) period for the air to expel and a pump to charge.

You have both fluid and film long before your system instrument sees it (a common myth) because fluid first "fills" the void then system resistance defines pressure so nothing is technically "dry" but for an insignificant time.

Then there is the dimension changing during the thermal growth- this will overwhelm any oil in any configuration until it completes.

That means for a point in any start up (OC or not, hot change or cold)- there is a period of time where no lubricant will have a tribological effect.

"Wear" resistance ( wear in this circumstance is defined both as a loss of mass due to abrasive forces removing base material and as a dimensional/geometric change due to physical impact leading to deformation) during this time is now being borne by the machine ( part) alignment/geometry/material properties and so forth.

So, both points of view are correct and incorrect at the same time depending on a lot of specifics but there is a point at initiation of movement/displacement up until thermal stabilization where nothing known will mitigate or eliminate or even slow down a certain percentage of mechanical wear in a machine.

Be confident in either way you choose to change your oil- both work very well.

 

[OilReport99]

An hour or two after the last drive, but I would do it with a cold engine as well.

 

[JeffKeryk]

I prefer cold if I am pulling the plug and filter. Hot engines are no fun to work on.
When using the MityVac, warm to kinda hot helps the draw.

 

[Zaedock]

I typically change oil based on the temperature of my beer.

 

[blupupher]

I don't think it matters very much. I do it cold because a cold engine is easier to work on than a hot one, and if you're changing transmission fluid, you want that to be cold so you can measure it and put back in the same amount. You don't have to worry about this with engine oil, but it's still easier to do the job cold than hot.

I use ramps, so I'm running the engine for at least a little bit, so the particles can still be suspended since the oil will have been flowing at least somewhat

Same here.
My truck I don't even have to put it on ramps, just do it cold. Sure it drains faster when warm, but when I do an oil change, I am in no hurry.

This gets brought up every so often, and never is there any proof either way.
For those that say they do it hot so "stuff" is suspended in the oil, well, don't you have a filter to catch "stuff", and unless the vehicle has been sitting for a decade, nothing will settle out since your last drive.

 

[Yah-Tah-Hey]

Probably only a two or three ounce difference between draining oil hot or at ambient. I prefer oil at operating temperature after a run up the highway and back.

 

[gathermewool]

Garage temperature. 50 to 80 F. Why burn your hands. 200,000 miles doing it like this and still doing fine.

Fumoto + top-mounted oil filter = no burning

 

[FordMan59]

I said I usually change mine cold which is true but, I do usually pull it up on ramps so I can get to the plug and filter easier so it usually runs less than 2 minutes. When I drain the oil I let it drain until there's only a drop every several seconds. While the pan is draining I pull the filter off and put the new one on. By the time I get that done it's usually time to put the plug back in and fill the sump.

 

[Loobit]

Let the engine get very hot and then let it sit overnight, then drain it cold. I noticed the oil level on the dipstick is most accurate after a hot Hemi has been sitting overnight. It reads higher on the dipstick than if you shut the engine off with cold oil and let it sit overnight, like as if the cold oil doesn't drain back into the pan as good as hot oil. This lets you drain out more oil. My LS1 does the same thing. Also do this same method to check the oil level after changing oil.

 

[Deleted member 89374]

I'm due for an oil change soon. I have a 2019 Ram 5.7L with under 10k miles. Wondering if it is best to change the oil while the engine is still hot (after it's had 5 - 10 mins to drain back into the pan) or after letting it cool off and sit overnight? I have heard several theories on the subject over the years but am interested to hear the opinions of others here.
Thanks

Here is how I do it:

I've built my own oil change ramps from wood. I made the front wheel ramps 2 inches taller than the real wheel ramps.

I start the car and go for a nice drive so I heat up the engine well. I go on the freeway for about 10 to 15 minutes. When I get back home I don't turn off the car. I put it up on the wooden ramps first, then I turn it off. The I remove the plastic engine cover while the engine is warm (it pops out easier). I don't touch the car until the next day. All that hot oil will drain into the oil pan along with any crud. So the next day I drain it and do my oil change. I live in NC, so it's nice and worm. The oil will flow out nicely even if the car had been off for 12 hours or more. That's about it. Is it the best way to do this? I don't know, but it beats the hell out of getting burned with hot oil.

 

[supton]

Like JeffK, back when I did topside it helped (a lot!) to do warm. I'm not sure what viscosity I used (5W40?) in the TDI but it was being sucked up through a straw. Warmer was better.

But for my other vehicles I've long done stone cold. 0W20 for the win in sub-freezing temps! Ha! [Yes I've done changes where I rolled around on snow and ice.] One car will burn me as the oil filter is under the exhaust manifold.

ABT can type it up better than I can. But years ago I figured that the filter was either doing its job, or the stuff that was not going to be filtered out was well-enough suspended that it wasn't going to fall out overnight (the finer the material the longer it stays in suspension). Plus by changing oil early and often it's not like the oil was ever all that worn out anyhow, nor "loaded up", nor was my engine generating lots of junk either (nothing old and worn out in my stable). The engines with the most miles seem to be driven hard and often and changed with cheap oil often with little care (taxi service and the like). Once I realized all that I decided it really didn't matter.

Now back in the days of non-detergent single grade oil, different story. Hasn't been that way in a long time.

 

[Snagglefoot]

I dropped an oil pan in a Ford 3.0 V-6 with 85,000 miles to change a leaking gasket. The pan was absolutely clean. There was no “crud”. Your oil filter takes care of that, especially if you do regular changes.

 

[Jocephus]

I used to do mine hot, but nowadays the vehicles I own are a PITA to work on so I just do it cold.

 

[Gene K]

Drive home and onto ramps. Come out two hours later and start oil.change.

I prefer warm without idling engine.

 

[Bryanccfshr]

Unless I am taking a sample I don’t care for a hot sump of oil to deal with.

 

[doublebase]

I used to think it mattered, now I really don’t. Just change it.

What I do now - instead of draining it when it’s smoking hot - is I just start it up and let it run for a minute. Just get it warm, not enough to burn yourself, just warm. Why punish yourself and make changing oil miserable by working under a hot engine? For what? What might be a few extra particles flowing out with hot oil? Even if true, not worth it in my opinion.

 

[free2d]

I do it cold overnight. Isnt particle will settle at the bottom of the pan?
Just take my time let it drip the whole afternoon.

 

[Brons2]

If I am taking a sample, I want the engine to be as hot as I can stand it as to minimize fuel dilution. I usually take the sample through the dipstick tube and then change the oil underneath the vehicle.

Otherwise - I live in Central Texas. 75% of the time, the oil is already warm, and I have changed a "cold" engine's oil when outside ambient is close to 100F. It comes out pretty fast regardless in July.

 

[wpod]

i Let it cool down (or warm up only a little) because I hate dumping hot Oil on my hand when I unscrew the drain bolt. Drains fine.

It makes you a man.

 

[wpod]

I would say hot could be the best but in real life it won't matter.