Oil Change: Hot or Cold?

[johnmyster]

It took a while to build oil pressure because you changed the oil and filter. It's going to do that regardless if the oil is change hot, warm or cold.

That wasn't a point. Of course I expected some time of empty oil passages. I was shocked at how long, but maybe I've forgotten in an age where most cars don't have OP gauges on the dash.

The point was, if dry restarts matter at all to the engine, why not choose to the change with as much oil in/on parts as possible? (The counter argument being, why not choose to use a method that we suspect achieves the highest draining of old oil.) If we suspect overnight draining gets more of the lube to the pan, the any dry restart concerns are an argument against the method. If it's got to run without pressure for a bit, why not have some oil in/on the parts by running it briefly, cold, before the change.

Any time the oil filer is removed, the galleries can drain out, regardless of the oil temperature. There is nothing you can do about that. One thing you can do is pre-fill the oil filter as much as possible. Or figure out how to crank the engine without it starting to prime the oiling system. I pre-fill the filter and fire it up, which cuts the time down to see the oil pressure. Not worried about it beyond that.

I'm well familiar. I pre-filled as much as I could, but the filter goes on nearly horizontal.

 

[kschachn]

For one thing “dry starts” don’t really matter. There is no truly dry start and oil changes are quite infrequent in the life of the vehicle. You may be alarmed by noises and what not but there is more than sufficient oil film on the parts to get you through the brief period while oil pressure rebuilds.

You really have no more nor less oil in the “parts” by either method, cold or hot.

 

[ZeeOSix]

That wasn't a point. Of course I expected some time of empty oil passages. I was shocked at how long, but maybe I've forgotten in an age where most cars don't have OP gauges on the dash.

It was one of your points, as shown by the edit in your post #92.

The point was, if dry restarts matter at all to the engine, why not choose to the change with as much oil in/on parts as possible? (The counter argument being, why not choose to use a method that we suspect achieves the highest draining of old oil.) If we suspect overnight draining gets more of the lube to the pan, the any dry restart concerns are an argument against the method. If it's got to run without pressure for a bit, why not have some oil in/on the parts by running it briefly, cold, before the change.

Dry starts aren't really "dry" of oil. A certain amount of oil clings to parts, and also remains inside journal bearings, regardless of how long the the engine sits after a hot shutdown. I have two motorcycles and one car I don't drive in the winter months, and they sit for months without being started - fuel stabilizer is added to the gas, and their batteries are kept charged. That would be like draining the oil for months, yet I'm not concerned when I fire them up again for the first time. Enough oil is going to cling to parts to provide adequate lubrication until more oil is supplied by the oiling system. Oil pressure doesn't directly equate to lubrication. Oil pressure only means oil is being forced through the engine by the oil pump.

One could argue that more oil clings to parts if the engine was ran cold for a few minutes, then shutdown. But if you then drained the oil cold you would have to drain it longer to get about the same amount of oil out if it was drained hot instead. So if you think more oil will cling if the engine is started for 5 min, shutdown cold and drained, then only let it drain for 15-20 minutes cold and not worry about the last 4-5 ounces of oil left in the engine. But I doubt there is any real proof that draining it that way, or draining it hot, or even firing up an engine after it sat for 3 months in the garage during winter storage is resulting in any amount of wear that will make any measurable difference.

 

[johnmyster]

That would be like draining the oil for months, yet I'm not concerned when I fire them up again for the first time.

When a car sits, do the oil filter and oil passages go empty? If so, then I accept that a restart after a filter change is no different than any other time the car has been at rest for moderate/extended periods.

My remark wasn't so much about if the passages go empty or they don't. Clearly they do, as evidenced by the oil running down my arm when I unscrew the filter. The remark was to acknowledge that this one element may inform one's take on the process, or not.

One could argue that more oil clings to parts if the engine was ran cold for a few minutes, then shutdown. But if you then drained the oil cold you would have to drain it longer to get about the same amount of oil out if it was drained hot instead. So if you think more oil will cling if the engine is started for 5 min, shutdown cold and drained, then only let it drain for 15-20 minutes cold and not worry about the last 4-5 ounces of oil left in the engine.

That's how the process works. I run the car long enough to pull it onto ramps, then shut down for the change. The oil has pretty good flow at ambient, so it comes out. (I know a person that would dump gasoline into the valve cover to rinse out the bad oil.) Two of my three cars have convoluted oil pans that don't fully drain so waiting for every drop to fall is pointless. When the stream turns into a dribble, the plug goes back in. While the oil was draining, I dealt with the filter. After that, oil goes back in topside and I pull of the ramps.

How long the process takes is largely independent of hot (100 C) or cold (20 C) oil.

My point was that your process might be dictated by your priorities. If you think the old oil is harmful and you want to get out every last drop, you may choose one method. If you dread the dry restart, you may choose another. To 100% fixate on the demise of either scenario is what this OCD forum is about, but neither captures the full truth. Both matter to a degree even if never to the extent they impact the longevity of the car.

Since I've been challenged on it, I think I'll improve my process. I'm going to warm the fresh 0w-20 oil in the microwave so that I can get it back into the engine faster. I'll also have my wife sit in the car so that she can restart as soon as the new oil is in. Both of those will help me get back to the restart sooner, mitigating as much as possible the dry restart scenario.

Or I'll take it a step further. I'll dump half the sump. Add a few quarts of 75w-140. Run the engine. Then dump the full sump and do the change. This way I know I'll have some sticky residual on standby.

 

[ZeeOSix]

When a car sits, do the oil filter and oil passages go empty?

If so, then I accept that a restart after a filter change is no different than any other time the car has been at rest for moderate/extended periods.

Not if the filter's ADBV works right. Not to say some galleries that might drain out that don't go the route of backflow towards the oil filter could still happen. Depends on the specific design of the oiling system for each engine design.

Some oil filters do have an ADBV that doesn't work that well, and therefore could allow some oil galleries above the filter to drain down every night while the vehicle sits until the next start-up. Use a good filter with a silicone ADBV is one way to mitigate ADBV malfunction.

That's how the process works. I run the car long enough to pull it onto ramps, then shut down for the change. The oil has pretty good flow at ambient, so it comes out. Two of my three cars have convoluted oil pans that don't fully drain so waiting for every drop to fall is pointless. When the stream turns into a dribble, the plug goes back in. While the oil was draining, I dealt with the filter. After that, oil goes back in topside and I pull of the ramps.

How long the process takes is largely independent of hot (100 C) or cold (20 C) oil.

My point was that your process might be dictated by your priorities. If you think the old oil is harmful and you want to get out every last drop, you may choose one method. If you dread the dry restart, you may choose another. To 100% fixate on one or the other is what this OCD forum is about, but neither captures the full truth. Both matter to a degree even if never to the extent they impact the longevity of the car.

Like I said earlier, I'm not worried about starting an engine that's been sitting for 2-3 months during winter storage because oil clings to parts and stays inside journal bearings for a very long time, so why would I be worried about the couple of times I've drained the sump when cold for 12+ hours and then fire up the engine a day later. People do what doesn't make them concerned or worried, regardless if what they do actually makes a difference or not. Carry on.

 

[kschachn]

Like I said earlier, I'm not worried about starting an engine that's been sitting for 2-3 months during winter storage because oil clings to parts and stays inside journal bearings for a very long time, so why would I be worried about the couple of times I've drained the sump when cold for 12+ hours and then fire up the engine a day later. People do what doesn't make them concerned or worried, regardless if what they do actually makes a difference or not. Carry on.

Sometimes there’s a lot of imagination about what’s going on inside the engine, whether it’s running or not.

 

[ZeeOSix]

Sometimes there’s a lot of imagination about what’s going on inside the engine, whether it’s running or not.

They might go bone dry if not ran every 12 hours.

 

[johnmyster]

Not if the filter's ADBV works right. Some oil filters do have an ADBV that doesn't work that well, and therefore could allow some oil galleries above the filter to drain down every night while the vehicle sits until the next start-up. Use a good filter with a silicone ADBV is one way to mitigate ADBV malfunction.


Like I said earlier, I'm not worried about starting an engine that's been sitting for 2-3 months during winter storage because oil clings to parts and stays inside journal bearings for a very long time, so why would I be worried about the couple of times I've drained the sump when cold for 12+ hours and then fire up the engine a day later. People do what doesn't make them concerned or worried, regardless if what they do actually makes a difference or not. Carry on.

Upfront, I don't think we're arguing as much as we see each others points in different proportions.

I don't worry about restarts after extended rest for two reasons. First, it's inevitable. (As are oil changes and dry restarts from filter changes.) Second, the oiling system is ready to function, quickly supplying lube flow.

In the case you highlight (extended drip times) we've drained as much oil away from parts as the engine will ever experience, and we've also extended the amount of time it will take before the oiling system provides/returns oil into any parts that have reduced inventory. I buy filters with nicer ADBVs and smooth plates for them to sit against because I pretend this matters.

Sometimes there’s a lot of imagination about what’s going on inside the engine, whether it’s running or not.

I blame the animated castrol commercials. I do know that some on this forum make major life choices based on pour point. I live above the pour point of every oil I've ever used. Oil tends to settle in bottles and in oil pans. I don't think it's far fetched to "imagine" that over time, there is less of it in the high places and more in low places. I also appreciate that adhesion and surface wetting is a thing. I also get that idle speed is slow and mechanical forces is thus lower on components, so it's not really a catastrophe to idle for a few seconds before lube supply returns. That doesn't mean I don't want to do what I can to minimize and mitigate it.

Completely unrelated, some in the thread might choose to do things in a way that reduces possible errors. I worry about someone walking into the garage and not knowing a car is a work in progress, or a toddler grabbing a set of keys and getting an idea. I replaced the famous oil cooler lines on our 2GR-FE a few months ago and had to to take a break in the process. (Talk about empty oil galleries.) I alerted my wife not to drive the car and went on to hide both sets of keys, because I didn't trust myself not to forget the car was missing some important parts should some unforeseen emergency distract me from the obvious.

 

[Steve_Crewdson]

But I check mine with a thermometer....The oil must be at 100 degrees F exactly then I change the oil.....

Sounds like someone who has checked ATF level on a Toyota AB60F.

 

[ZeeOSix]

Upfront, I don't think we're arguing as much as we see each others points in different proportions.

Just showing my viewpoint from all angles. Not trying to change anybody's mind on what they think is best for them - only they can decided that based on the information available. Pretty much how all aspects of life works.

I don't worry about restarts after extended rest for two reasons. First, it's inevitable. (As are oil changes and dry restarts from filter changes.) Second, the oiling system is ready to function, quickly supplying lube flow.

But as I pointed out, all the oil in the engine has drained down and off of parts as much as possible every time an engine is shutdown and allowed to sit for extended times. Just shutting down an engine hot and letting it sit overnight probably gets to the point where the oil film left behind is going to stay there a very long time (like months). I don't have any controlled test data to show it, but regardless if an engine sits for 24 hours or for 24 days, the same remaining oil film will be left on the parts, regardless if the engine was shutdown hot or cold. I will agree that if an engine was started cold, ran for only 5 minutes and then shutdown, then the oil was drained cold for 15-20 minutes, that there might a a bit more oil film left on parts because it would drain off of parts slower cold than if it was hot. Will it make a difference in wear on the next start-up ... probably not. But a controlled multi-million dollar test program might prove it one way or the other.

In the case you highlight (extended drip times) we've drained as much oil away from parts as the engine will ever experience, and we've also extended the amount of time it will take before the oiling system provides returns oil into any parts that have reduced inventory.

The amount of time it takes before the oiling system provides return oil to any parts is not based on if the oil was drained hot, warm or cold. It only is based on how much oil has drained out of the oiling system galleries after the oil filter is removed to install a new oil filter. Oil will drain out any time the oil filter is removed, regardless of the oil temperature.

I do know that some on this forum make choices based on pour point. I live above the pour point of every oil I've ever used. Oil tends to settle in bottles and in oil pans. I don't think it's far fetched to suppose that over time, there is less of it in the "high" places in a motor than there was during operation. Yet I also appreciate that adhesion and surface wetting is a thing.

Mentioned above, oil will drain off of parts and leave a constant layer of oil film. If the engine was ran cold for a few minutes, and the oil was still "cold" on those parts, it will probably take a little longer for it to drain off and leave the same resulting thickness of oil film.

Completely unrelated, some in the thread might choose to do things in a way that reduces possible errors. I worry about someone walking into the garage and not knowing a car is a work in progress. I replaced the famous oil cooler lines on our 2GR-FE a few months ago and had to to take a break in the process. (Talk about empty oil galleries.) I told my wife not to drive the car and went on to hide both sets of keys, because I didn't trust myself not to forget the car was missing some important parts should some unforeseen emergency arise.

Put a big sign on the windshield or on the steering wheel that says "DO NOT DRIVE ... CAR IS BEING WORKED ON !!" or something along those lines if you think someone not knowing what's going on with the car is going to try and drive it.

 

[johnmyster]

Mentioned above, oil will drain off of parts and leave a constant layer of oil film. If the engine was ran cold for a few minutes, and the oil was still "cold" on those parts, it will probably take a little longer for it to drain off and leave the same resulting thickness of oil film.

I don't disagree, the time it takes to refill the oiling system from empty isn't based on most recent shutdown temperature. That would be silly. If I asserted such, my apologies

If I read correctly, in your mental model drain off happens quickly (based on temperature) to some minimum stable film. That minimum film is still sufficient to protect for however long a dry start takes. A motor has a high number of minimum stable film restarts over its life, so no harm in one more per OCI.

In my mental imagination model, the drain off is quick at first but decays, continuing on for a long time until the same minimum stable film is realized. The rate is asymptotic. I imagine the minimum stable film is inevitable in some scenarios, but more film is better, especially in the case of a dry restart. How much better? Can't say. Dad always said that most engine wear occurs during startup and especially on an empty filter...thus we prefill.

FWIW, our truck isn't a daily driver. It primarily pulls a camper. I try to drive it every two weeks. I don't pretend the startup condition is too much different after a day, a week, or a month. I sure hope not. I'm not going out there and starting it up on days it isn't driven.

 

[KrisZ]

I think the solution is not to change the oil. I think Saturn did it right, burn enough so the owner just keeps adding oil.

 

[ZeeOSix]

If I read correctly, in your mental model drain off happens quickly (based on temperature) to some minimum stable film. That minimum film is still sufficient to protect for however long a dry start takes. A motor has a high number of minimum stable film restarts over its life, so no harm in one more per OCI.

Yes, that's my take. If the oil pressure is achieved in 5-6 seconds or less (probably even 10 sec or less), the remaining oil film will give adequate lubrication until the oiling system is fully flowing again, even if the oil was drained for say a day. Or even in my case with a few vehicles that sit for 3-4 months over the winter months without ever being started. It's something I'm not concerned about.

In my mental imagination model, the drain off is quick at first but decays, continuing on for a long time until the same minimum stable film is realized. The rate is asymptotic.

That's what I've been saying many times in this discussion. Only some good testing would determine what the oil film layer left behind vs drain time vs oil viscosity and temperature would be. Maybe a test like that has already been done, I've never search for one. My bet is if the oil drained overnight in a hot shutdown engine, the left behind oil film will be at it's stable minimum within 12 hrs .... just my gut feel. In other words, if the oil drained off of parts when hot (like cam lobes, followers, etc that are open and not trapping oil like in bearing journals or between piston and cylinder), it's not going to take very long to achieve the ending stable film thickness on those parts. Journal bearings will retain an oil film thickness easier than the face of a cam lobe for instance. People here have said they have torn down engines that have been sitting for years in a garage or junk yard, and still find a good oil film in all the journal bearings.

I imagine the minimum stable film is inevitable in some scenarios, but more film is better, especially in the case of a dry restart. How much better? Can't say. Dad always said that most engine wear occurs during startup and especially on an empty filter...thus we prefill.

Based on many cold start and warm-up studies discussed in this forum, there is also wear in the warm-up cycle going on even if the oil and filter wasn't changed. That happens every time the engine is started cold and warms up. The cumulative wear from warm-up may exceed the cumulative wear from start-ups after an oil change since the number of OCIs vs engine start-up is much lower. Look at the number of engine start-ups & warm-ups in a 7500 mile OCI. Theoretically, a car that is short tripped vs one that is driven many miles on every start-up should have higher wear from the increased number of cold start-up & warm-up cycles over an OCI period.

Yes, you can't do much about the oil draining off of parts every time the engine is shutdown and it sits for hours, days or months. Even if an engine is turned over without starting in order to prime the oiling system and get oil flowing, those parts are still moving the same as if the engine was actually fired up. Only difference would be the level of force on some of those parts, like rod and crank journal bearings. But those forces are relatively pretty low at a start-up with minimum throttle opening (engine load). But as mentioned above, oil film pretty much remains in journal bearings for years (junk yard engine example above), so that's a benefit. Other parts like cam lobs and followers have a super hard surface and that helps reduce wear. Plus the left over tribofilm AW layer on those parts helps mitigate wear in these kind of start-up (and warm-up) situations. Lots of stuff going on.

FWIW, our truck isn't a daily driver. It primarily pulls a camper. I try to drive it every two weeks. I don't pretend the startup condition is too much different after a day, a week, or a month. I sure hope not. I'm not going out there and starting it up on days it isn't driven.

Yep, I don't worry about that either. All you can do (without going wild, like a pre-lube system) is to pre-fill the oil filter to help the oiling system fill a few seconds faster and build up oil pressure. Trust the oil film and the tribofilm AW layer.

 

[KrisZ]

There is tons of oil left in the cylinder heads and on the cam lobes. When I did the rocker arms on my Pentastar, I got the wrong rockers the first time and the car sat for a week before the correct ones arrived. The lobes were still nice and wet with oil.

All these “dry starts” are only in people’s imagination, I have yet to see it in real life.

 

[ATex7239]

Engine builders and oil manufacturers throughout history have never considered the nuances of oil changes… glad YouTube experts finally came along to line this all out for us.

 

[KrisZ]

Engine builders and oil manufacturers throughout history have never considered the nuances of oil changes… glad YouTube experts finally came along to line this all out for us.

Yeah, before YouTube we were just primitive monkeys stumbling in the dark, not even realizing the dangers of changing the oil.

Good thing the enlightened age has arrived

 

[ATex7239]

Yeah, before YouTube we were just primitive monkeys stumbling in the dark, not even realizing the dangers of changing the oil.

Good thing the enlightened age has arrived

We are all better for it.

 

[Kantaro]

It's more important to have your drain plug aligned with the Earth's magnetic field so that it helps pull ferrous particles from the engine

 

[CheezWhiz]

impossible question- how frequently do cold-changed engines actually wear out compared to warm-changed engines?

 

[14.1 Grms]

It's more important to have your drain plug aligned with the Earth's magnetic field so that it helps pull ferrous particles from the engine

A step you can skip if you're using Magnatec - because it has intelligent oil molecules® that know you're doing an oil change and get a double armful of the bad stuff on the way out regardless of the oil temperature.