Engine oil changes: hot or cold?

I have always changed engine oil when its hot, or at least still quite warm after running the engine. I seem to recall as a kid it was always the way it was done. I am wondering whether this was a result of higher viscosity single grade oils used back in the day.

Right now it will be more convenient to do an oil change with a cold engine, via the oil change pumpout system. Its easy to turn the pump off, come back after 30 minutes and turn it back on to get the last little bit out.

Just curious as to what most folks do, hot or cold changes. And if anyone like Ski has sound reasons for not doing cold oil changes. I've heard of particulates not draining out with cold oil but figure that if there were any particulates around then they would end up in the oil filter, so not too concerned about that.

I like to change it warm after the engine has run for a bit but the oil has had a chance to drain back into the pan. Easier on the pump and the particles should still be in suspension. And those particles that may have settled out should move out with the oil easier if the oil is warm.

At least that is my reasoning.

One of the biggest reasons for doing it with a warmed up engine is that cold oil is thick, and it can burn up your oil change pump. Been there, done that. Otherwise, not a big difference cold or warm.

Ski in NC said:

One of the biggest reasons for doing it with a warmed up engine is that cold oil is thick, and it can burn up your oil change pump. Been there, done that. Otherwise, not a big difference cold or warm.

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I agree with Ski, but its not because I know any better. I visualize the process. Water will settle to the bottom. So a cold change should get it out. Particles will settle so they should also be removed. All residual oil should drain down on a cold pump out. So any suspended particulates that don't drain down hot should hit the bottom cold.
Having said all that I pull hot samples for analysis prior to oil changes so it is all mixed up.
But what the heck, I am guessing.

My line of reasoning is the particles that may settle to the bottom, as well as the oil, are more likely to move, flow out easier if the oil is warm as opposed to how cold thick oil flows.

But in the long run it probably makes little difference.

I always do it hot, but see what the manufacturer recomends. I've never seen one that said cold.

I have not found a manufacturer recommendation for warm (or cold). But I'll likely do this change warm after all because I want to do an oil analysis, and warm is going to be better for obtaining a good sample.

15% or more of modern oil is the additive package.

A good portion of that is a detergent.Esp with newer oils.

Detergent keeps the big crud in suspension so the oil filter can grab it.

The fine stuff that passes the filter still requires removal for longest engine life.

A long 5-8+ hour run allows the detergent to re grab the fine stuff stuck to the sides and bottom of the oil pan and get it back in circulation.

This happens with every long engine run , weather you are changing the oil or not.

"Best Practice" would seem to remove it every time the oil is changed.

Or use a centrifugal bypass filter system and catch it as its formed.

Might be worthwhile to take the extra effort after a long days run to change the oil hot and dirty ,
so the beast can "live long and prosper".

Like Ski and others, I start changes after a short run to heat up the oil. We use the installed pump-out system.


FWIW, I usually only do the "outie" when oil is warm. I usually don't do the "innie" (fill) and filter changes until the next day, when the engine room and filters are a more comfortable temperature.


-Chris

I don't believe it makes much difference as long as the pump can handle it easily.
I used to do gassers hot as the cheap pump I had wouldn't handle cold very well.
Current X-Change pump handles cold / warm very easily and is away from engine so heat not much of a problem.

It might make more of a difference if you are pulling a sample for analysis...

Blackstone's sampling recommendations include....
"Run the engine (don't just idle) before you take the sample to get the oil at operating temperature — about 20 minutes should do it.
Getting the oil up to operating temperature should help cook out any normal moisture or fuel build-up."

I'd be interested if anyone has done it both ways and found any difference in the amount you get out? (w/ similar dip stick oil levels to start)

I change when hot. That is .. run for several hours not just run a bit at the marina. The additives, carbon and "dirt" (foreign matter) is much more in suspension when the engine is hot. And draining quickly before much "stuff" settles where it will remain in the engine is a goal for me.

My Mitsubishi Owners Manual says "Immediately after shutting down the engine (when the oil is hot) remove the oil pan drain plug." Changing when cold or warm is not mentioned.

I think many or most likely most manuals will say do it hot. Cars, motorcycles ect. Probably hard to change your lower unit OB oil hot though. But if you really need or want to change oil cold I don't know to what degree you've really done what needs to be done. The biggest reason to change oil is to remove the carbon and acids that form from moisture over time. But carbon (the black stuff) is an abrasive that wears engine parts like bearings and that's job #1 as far as I know.

So definitely change hot.
And IMO cold thick oil being a PITA has nothing to do w it.

ranger42c said:

Like Ski and others, I start changes after a short run to heat up the oil. We use the installed pump-out system.


FWIW, I usually only do the "outie" when oil is warm. I usually don't do the "innie" (fill) and filter changes until the next day, when the engine room and filters are a more comfortable temperature.


-Chris

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Thanks. That's one of those clearly obvious things once I see it, but never thought of it before.

And my oil change pump will not pump cold oil either.

Oil analysis lab don't seem to care...I don't care except hot oil pumps and pours easier.

As for engine longevity...like most discussions here....flyshi*.

I've done it both, my old clam crusher is still happy. Meh.

I have always done it on a warm engine just because it is a lot easier to pump the used oil out of the dipstick tube when it is warm. I never have given it a lot of thought however. The arguments for doing it on a hot (instead of just warmed up as I have done) engine make a lot of sense.

I often do it cold because my pump will move cold oil with no issues. And a cool engine room is more comfortable to work in.

jleonard said:

I often do it cold because my pump will move cold oil with no issues. And a cool engine room is more comfortable to work in.

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Cool is good!

But until I buy an electric pump...I work up the same amount of sweat....hot ER or pumping molasses.....

psneeld said:

Cool is good!

But until I buy an electric pump...I work up the same amount of sweat....hot ER or pumping molasses.....

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Has anyone definitively proved whether hot oil is thinner than cold. One just assumed it was, but when you think of the purpose of the various elements in multigrade, which many of us use, (yes, I know Lehmans were originally run with 30w single grade, so don't bother repeating it), then it is even possible, if they do what they claim to, the oil might get thicker when it gets hot..? I never thought much about that.

This suggests that the above is not correct, and the assumption that cold oil, even a multigrade, is thicker when cold, is in fact correct.
Bugger, I was hoping not.

Multigrade oil has a flour like substance that gets thicker as it heats.

In your galley take a cup of oil and pour it thry a small funnel and time it.

Heat the oil in the microwave and repeat.

Do the same with single weight and watch the difference.

I have definitely proven it to myself.


Take any oil cold and pour it...it doesn't splatter....heat it to 180 and it sure will.


No science..just practicality.

All motor oils are thick when cold and thin when hot. There is a viscosity vs temp chart for each, with the plot for multi vis oils a bit flatter than single vis.

Anyone with Detroits has probably experienced trying to pour a cold jug of 40wt into an engine in the winter. The stuff barely comes out of the jug.

...

Gosh, Australia or FL cold could be Canada warm. Also, on my engines the engine mounted hand pump works much better to get out the last few liters with warm oil that the pump won't suck out.

Tried once after engine was running for 5-10 minutes only. Took me almost one hour to suck the 13 liter 15-W40 via the dip stick with my hand vacuum pump.
Made that experience I do it since then hot (engine at least one hour under load) ...



best regards / med venlig hilsen
wadden

I have a hose connected to the drain plug and an "oil x changer" pump that doesn't mind cold thick oil.
Years ago when I had to go thru the dipstick it had to be really hot.

Hot! Hot! Hot!

Hello Cal sailors

My original cal cruising 46 hull no 5 came with a Perkins 4.236 engine

For years I could only do max of 14 to 1600 RPM on cruising (6-7 knots)

After much trouble turns out the injectors where clogged or partially clogged

And the marine growth build up in the heatexchanger impeded cruising at higher RPM

cuz of over Heating


NOW that I've got all that resolved, the boat wants to fly

Now I can do 2200 to 2400 RPM in a heartbeat and cruise at 8.5 to 8.7 knots

And water gushes out in the back exhaust like Niagara Falls

What I have discovered now is,

After a 4 hrs trip to Catalina island, (from Marina del Rey ) a mere 28 nautical

Miles away, my engine oil is LOW and requires a top off 1 to 1.5 quarts of oil!

ITS BURNING OIL at much higher rpm

The engine runs smoothly, no overheating no black or blue smoke, good sound

I do see a slight white fog coming out of the exhaust but that may

Be from the coldness of the water and the fact the exhaust spends 1/3 of time

Underwater while cruising

But this oil loss is really annoying and worrisome

The engines runs so well though

The engine hours barely reads 1250 hrs

Had the injector pump and injectors rebuilt last year

The oil and antifreeze is clean, no cross contamination, no visible leak anywhere

Any advise?

I have not tried running at just 15-1600 to see if this persists

Would appreciate any thoughts




Edwin
Cal Cruising 46
MdR

Engine oil cooler oil leak?

Perkins 4.236 consuming oil

BruceK said:

Engine oil cooler oil leak?

Click to expand...

How do I diagnose an oil cooler leak?




Edwin

I`m no mechanic, but if you pull the oil cooler you may be able to determine if oil is leaking into the water. Maybe a pressure test by a radiator repairer.
Hopefully someone more mechanical contributes to your issue.