Oil change on cold engine

[teamextreme]

It's one of those urban legends that has some truth to it that no one understands. Changing the oil while hot does remove more of the dirt and contaminants, because the sediment/particulates that would normally settle on horizontal surfaces is reabsorbed into the moving 200°f oil.

Unfortunately, that's just a secondary benefit. The real reason you change your oil hot instead of ice cold is because you want every surface of every moving part coated in a thin layer of oil before you drain it. Otherwise you're starting your engine effectively dry (it takes about 1-2 full seconds to fill an empty oil filter housing, during which time you have zero oil pressure).

Are you driving vehicles with no oil filters? You claim sediment/particulates will be put into suspension in hot oil. True, if you didn't have a filter, which is trapping all those things.

On the secondary benefit, you're claiming that a hot oil change will keep oil on the engine parts for when you start it next. That makes no sense at all. Ignore doing any kind of oil change, what is happening every time you start a cold engine? The same scenario you are describing. Yes, all the oil has run down into the pan, and yes it's the hardest time on an engine, but doing a cold oil change has no effect on that, you would have started it cold next time weather you changed the oil or not.

 

[66HertzClone]

If you're doing it cold, try to get as much oil into the filter before you put it on the engine. That way, when you start it, there's less lag for it to get to where it's needed. If the oil filter screws on vertically with the opening at the top, this is a piece of cake, and I fill that sucker up. If it's at an angle, then I'll put a bit less in it.

In general, I'm a fan of doing it when the engine is warm-ish but not hot. That way, there's still oil on most surfaces, and the lag for circulating oil is less on start up after the oil change.

I remember years ago working on a 280Zx, one of the turbocharged one. If anyone remembers these the oil filter location was on the rear of the engine accessible only from above. The customer informed me the dealer had always filled the filter with oil prior to installation.

I looked him in the eye and said that’s just not possible. I explained the position and obstructions that would make this impossible. He continued to insist that this is what the dealer had been doing.

Eventually he called the service department to confirm, it wasn’t long before he approached m, apologized and said the dealer had confirmed what I had been telling him.

I saw him last week in my shop having the oil changed in his current vehicle, we laughed about our first meeting nearly 30 years ago.

 

[DGersic]

Will less likely strip the shoulders on a hot oil plug as it will come out easier when hot.

Fumoto valve. No stripped pan threads ever again.



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[Miss the Pontiacs]

I prefer to do it warm because the oil is a little thinner and comes out quicker, and because a good deal more of the contaminants will still be in suspension. Its certainly ok to do it on a cold engine, but there may be some stuff on the bottom of the oil pan that doesn't come out. If you really don't want to take it for a drive, change the oil as-is. Since you're on lock-down however, why not spend the time and take it for a rip??

It's one of those urban legends that has some truth to it that no one understands. Changing the oil while hot does remove more of the dirt and contaminants, because the sediment/particulates that would normally settle on horizontal surfaces is reabsorbed into the moving 200°f oil.

Unfortunately, that's just a secondary benefit. The real reason you change your oil hot instead of ice cold is because you want every surface of every moving part coated in a thin layer of oil before you drain it. Otherwise you're starting your engine effectively dry (it takes about 1-2 full seconds to fill an empty oil filter housing, during which time you have zero oil pressure). You can do more wear to an engine starting it five times driving ten miles, than starting it one time and driving five hundred miles. Now imagine starting that engine with no oil for several seconds.

If you ever build engines you understand the importance of having oil pressure before the motor even starts for the first time by priming it by hand. I watch these obnoxious shows like *** Monkey (Fast N' Loud) and when I see them fail to get a new engine to start within 1-2 seconds, you realize they've already done permanent damage to the motor.

So, the answer is in the tribal knowledge: you change oil when hot to remove contaminants, but mostly to prevent any damage to the engine while the oil filter pressurizes. If you have a FRAM type screw on filter, always make sure to fill it up, let it soak, and then fill it up again before installing it. The Germans made that nearly impossible with their MANN cartridge filters on their vehicles these days because they only seal when the o-rings make contact with the housing.

I agree totally with a warm/hot change. I have to drive up on ramps anyway so why would I do a quick 3-5’ drive and change cold. This would take the particulate out of the pan and disperse it anyway. When you go to an oil change place is the oil not hot from the drive over? I also fill or at least partially the filter, then I can lubricate the seal as well at the same time. While it is draining I get everything else ready and once that is done the oil has drained. Now if I had a lift and it was sitting up there waiting and cold, I might give it a cold change. But it would be my first cold change.

 

[sberry]

Is there pixies living in these engines? **** like this gives people the feeling they know something about cars I guess.

 

[Balor]

Modern oil is designed to hold contaminants (acids, carbons, trash) in suspension when it is hot. When oil is cold/worm it allows contaminants to fall/drop to the bottom of the oil pan.

 

[Jackfre]

The compromise position on this is to heat the pan. Get a 100W incandescent drop light and hang it under the pan overnight. Dad's happy! You're happy! What could go wrong?

 

[Tonyuk]

If you spent any time rebuilding engines and priming them by hand, you would realize the inordinate amount of time required for oil to pass through a new filter before you get adequate oil pressure. Doesn't matter whether it's a cartridge or a screw on.


The hot oil versus cold oil has to do with sediment in the bottom of the pan. The more dirt you get out, the better the filter will do over the next 5,000 miles.

There's a right way to do things, and a lazy way to do things. People make excuses so they can do it the lazy way and cut corners.

Nonsense,

If the engine would suffer damage from being started with an empty filter then the engineers who built the car would design the filter in such a way that it was able to be filled before installation. Since not all can be done like this its clearly not a problem.

If you have sediment in your pan you have a more serious problem than what an oil change will fix.....

 

[double-d]

Nonsense,

If the engine would suffer damage from being started with an empty filter then the engineers who built the car would design the filter in such a way that it was able to be filled before installation.

-----> Uhm, can someone explain the reason for anti-drainback valves in screw-on filters?
If dry filters are not a issue..... why the anti-drainback valves?

https://www.pgfilters.com/blog/function-anti-drain-back-valve-oil-filter/

FWIW, I warm my engines and pre-oil my filters. If the filter installs horizontally, I simply drain back out enough oil that it doesn't pour out when installing.Saturated pleats reduces time for oil to hit moving parts.

Also, I typically use magnets on my filters.......but that is for a different thread.

 

[finn]

Have any of you actually taken apart an engine? I have yet to see a main or rod bearing on an engine that has been run within the past decade that doesn’t have an oil film on it. It doesn’t take much oil to provide a hydrodynamic film on a bearing. Prelubing a new engine is done primarily to insure that the oil pump primes, which isn’t a problem with an engine that has been previously run and is simply undergoing a routine oil change.

Filling the dry filters is a feel good exercise. If you feel it’s a must, carry on, I suppose.

By the way, during my career in Diesel engine R&D, one of the fill in projects my team had involved measuring wear using radiated engine bearings and piston rings. Part of the test sequence included start up (with and without filling the filters). Results: start up oil pressure lag was not a factor in bearing wear. Normal assembly practices, ie coating the bearings with fresh oil, provided adequate protection until normal gallery pressure built up.

Oil pressure and flow is necessary to provide cooling to the bearings. The actual loads are supported by the hydrodynamic oil wedge developed within the journal bearing interface. Running a few seconds won’t materially affect this wedge. Running for extended periods without pressure increases heat, or rather doesn’t allow the heat to be carried away, which in turn drops the local viscosity, which reduces the oil film thickness.......

 

[ddawg16]

do it cold, just means you can have another beer while it is draining

Nice to know I'm not the only one who thinks that way

 

[bwringer]

For a while there I was afraid that we'd have an oil thread without vehement argument, ire, dudgeon, or umbrage taking.

Glad to see that the Laws of the Internet regarding oil threads have not been broken yet.

 

[lilredex]

Have any of you actually taken apart an engine? I have yet to see a main or rod bearing on an engine that has been run within the past decade that doesn’t have an oil film on it. It doesn’t take much oil to provide a hydrodynamic film on a bearing. Prelubing a new engine is done primarily to insure that the oil pump primes, which isn’t a problem with an engine that has been previously run and is simply undergoing a routine oil change.

Have to agree with this.

I spent a few years in an engine rebuilding place and all the returned cores were always well lubricated upon tear down. The "new" ones were lubbed with Lubriplate and run in on an electric motor powered stand to check things out.

It only took seconds to obtain full oil pressure.

 

[teamextreme]

When you start a motor cold, you have some residual oil on the engine to be sure (particularly with synthetic), but the filter is already soaked and oil pressurizes in a normal amount of time.

If you spent any time rebuilding engines and priming them by hand, you would realize the inordinate amount of time required for oil to pass through a new filter before you get adequate oil pressure. Doesn't matter whether it's a cartridge or a screw on.

Running the engine and having fresh oil on every moving part prior to the oil change keeps the metal to metal contact limited until the oil soaks, and pushes through the new paper filter.

The hot oil versus cold oil has to do with sediment in the bottom of the pan. The more dirt you get out, the better the filter will do over the next 5,000 miles.

There's a right way to do things, and a lazy way to do things. People make excuses so they can do it the lazy way and cut corners.

Ah, but now you're talking about pre-filling the filter, which is not what this post is about (although it's getting thrown in). This discussion, and your implication, is that a hot oil change will help in this matter over a cold change, but in fact you are actually calling for pre-filling the filter to prevent this supposed damage (which certainly could be argued as being beneficial), and then using this contorted logic to imply anyone doing otherwise is lazy.

 

[Rt jam]

It's one of those urban legends that has some truth to it that no one understands. Changing the oil while hot does remove more of the dirt and contaminants, because the sediment/particulates that would normally settle on horizontal surfaces is reabsorbed into the moving 200°f oil.

Unfortunately, that's just a secondary benefit. The real reason you change your oil hot instead of ice cold is because you want every surface of every moving part coated in a thin layer of oil before you drain it. Otherwise you're starting your engine effectively dry (it takes about 1-2 full seconds to fill an empty oil filter housing, during which time you have zero oil pressure). You can do more wear to an engine starting it five times driving ten miles, than starting it one time and driving five hundred miles. Now imagine starting that engine with no oil for several seconds.

If you ever build engines you understand the importance of having oil pressure before the motor even starts for the first time by priming it by hand. I watch these obnoxious shows like *** Monkey (Fast N' Loud) and when I see them fail to get a new engine to start within 1-2 seconds, you realize they've already done permanent damage to the motor.

So, the answer is in the tribal knowledge: you change oil when hot to remove contaminants, but mostly to prevent any damage to the engine while the oil filter pressurizes. If you have a FRAM type screw on filter, always make sure to fill it up, let it soak, and then fill it up again before installing it. The Germans made that nearly impossible with their MANN cartridge filters on their vehicles these days because they only seal when the o-rings make contact with the housing.

ABSOLUTELY AGREE with hot.

More particulates suspended in warm oil since was run very recently.

Also if instant oil pressure if important to you. Drop oil when warm, install prefilled filter, refill and start it soon after.
This method save a few seconds of having no oil pressure, which is obviously not important to so many here but I'll take every fraction of a seconds. Dry starts are the ONLY thing wearing our engines.

Any arguments regarding introducing dirt into a new filter. If you are that much of a *****, then you should not be changing your own oil.

 

[Legion Prime]

Why not speed things along AND prevent running the engine dry by taking the filter off while the engine is running which will speed up draining the old oil. Meanwhile have a helper start pouring in the new oil and once you see the new oil start coming out spin on the new filter, shut down the engine and then add new oil as needed to hit the FULL line on the dipstick. Jesus you people like to overcomplicate things.

 

[unslow1]

I change them hot or cold. Personally I prefer cold after sitting overnight. If your crank and rods bearing didn't have oil constantly sitting on them a car would spin a rod every morning.

 

[king nero]

I tend to do my oil changes when I got time. Most of the times, they leak out overnight, or at least an entire afternoon if I need the car the next day in the morning, then I'll fill her up again in the evening.

As said before, modern oil and filters do not tend to have much **** in them. and if they do, you have got other problems.

 

[Dutch01]

The OP refers to an oil change after his car has been standing for a long time. Starting the engine to warm it up will just circulate the contaminants being referred to in the engine an any case. Just drain cold and have the beer as suggested before putting oil plug back.

The comments about oiling the contact surfaces when rebuilding an engine are irrelevant in this scenario. Yes I agree it must be done when doing a rebuild as parts are normally cleaned with a solvent, removing the protective oil film on moving parts.

 

[AldeanFan]

Op following up.
This was an interesting discussion. There is not a clear consensus but I think that is because it doesn’t really matter. No one is able to say definitively that they did only hot or only cold oil changes and the engine failed as a result.

The car was already up in the air for other work so I did the cold oil change, old oil drained out, filter replaced, new oil in, no drama.
The oil filter goes on the side of the block so filling it is not an option, but I usually pour about a cup of oil in and what i spill gets rubbed on the gasket.

This is a 1957 292 Y-block so it originally had a canister filter, but it’s been converted to a spin on filter. Now it takes the same filter as a 302. I use 15w40 diesel oil, Motomaster brand which is rumoured to be repackaged Rotella at 2/3 the price.

And here are some pictures.

Sent from my iPhone using Tapatalk

 

[Falcon67]

I change the race engine, trucks, generator, mower, etc all cold. Have no desire to work on a hot motor. Put a pan under it, pull the plug, go have a beverage. It's not a NASCAR pit stop.

 

[Rt jam]

Anyways it was a healthy discussion on pros and cons of each method. Your method sounds extremely messy. Your superhero cape would surely be covered in oil.