Oil Volume vs Temperature

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As noted here (I think) and in the “Engineering Toolbox”, oil volume expands with increasing temperature. And if I’m interpreting the “Toolbox” graphs correctly the increase is of some significance: from room temperature to 100C on the order of 5-6%.

So when we buy a 5-quart jug of oil, at what temperature do we think the oil volume is based? An oil’s PDS will generally show a density factor (presumably vs water) at about 15C, or roughly room temperature. Is it reasonable to assume this is 5-quart volume temperature at which an oil is bottled?

If this is so, let‘s assume we change the oil with the specified amount and the following morning, when the sump has cooled, add a bit more to bring the dipstick to the “full” mark. If we then take a long Interstate run and check the oil does seem reasonable to assume the oil level will be 5-6% higher than when cold? I realize this isn’t much, but on a 5-quart sump it’s still and extra 1/4 quart which should be noticeable. Does anyone see this?

And does this suggest that filling a cold sump to absolutely full is not necessarily the best approach? Maybe using the specified amount and being content if the result is a bit short of full is better?

I realize we’re kind of in the weeds here, but with some discussion about fuel dilution and rising sump levels I wonder if this could be a factor.

Thanks.
 
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2,182
Location
South Carolina
I never put my oil up to the full mark on the dipstick when I change oil. Usually 1/2 or 3/4. If I take it out on the highway and get it hot and check the oil it gains about 1/4 on the dipstick. I've been told (here) that's impossible but it's what I've seen.
 
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Upstate
35 years ago, I would receive bulk oil into warehouse tanks that was fresh from being blended. It was blended warm, so it could be received at say 25°F above ambient, or more during winter. We had a procedure which required recording the temperature of the oil in the tank before and after receiving it. Data was applied to tables, and adjustments to the inventory were made. As I recall, the adjustments were fractions of one percent. I'd have a two or three gallon adjustment on a 2500 gallon delivery in a single tank.
I really think thermal expansion is not something with which you normally need to concern yourself.
 
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2,114
Location
WA
Manufacturers consider this when designing. 🔧

most everyone or oil places change oil and fill up to F. The owner's manual doesn't say heat the oil to 200F and fill up.
 
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57
Location
Colorado
I never put my oil up to the full mark on the dipstick when I change oil. Usually 1/2 or 3/4. If I take it out on the highway and get it hot and check the oil it gains about 1/4 on the dipstick. I've been told (here) that's impossible but it's what I've seen.

You're not “gaining” oil. It’s just expanding with temperature so it seems like you’re gaining oil Which is normal. If you check the level again in the morning after your car has cooled back down it should be back to where you started....assuming you didn’t burn any oil on the drive.
 
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998
Location
New York
i stay out of the weeds
not worth the thinking and it does not matter

Oh boy, are you on the wrong site!
haha.jpg
 
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26,411
Location
PNW
If this is so, let‘s assume we change the oil with the specified amount and the following morning, when the sump has cooled, add a bit more to bring the dipstick to the “full” mark. If we then take a long Interstate run and check the oil does seem reasonable to assume the oil level will be 5-6% higher than when cold? I realize this isn’t much, but on a 5-quart sump it’s still and extra 1/4 quart which should be noticeable. Does anyone see this?

Of course the oil level goes up on the dipstick when the oil is fully hot (fluid volume expands from heat) - I see it on every car, truck, motorcycle, etc I've ever owned. Some vehicles have cold and hot level markings on the dipstick for this very reason.
 
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2,182
Location
South Carolina
You're not “gaining” oil. It’s just expanding with temperature so it seems like you’re gaining oil Which is normal. If you check the level again in the morning after your car has cooled back down it should be back to where you started....assuming you didn’t burn any oil on the drive.
I realize this like the ATF dipstick has a hot and cold range. Never said I was "gaining" oil.
 
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1,528
Location
California
Usually there's a big volume between the ADD and FULL marks on a dipstick, like at least 1 quart on most engines. So 5-6% expansion (if that is accurate) is insignificant. If that much difference could/does cause problems in your engine, it needs repair of some kind. Just keep the oil level between the marks and find something else to worry about. Personally I've never seen much of a difference on a dipstick between cold and full temp.
 
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387
i believe we want it so that when our oil is cold it is preferably at the full but it can be anywhere between min amd full. the manufatures and etc compensate for the fact that when the oil is at its hottest it may pass the dipstick full mark which is totally fine
 
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26,411
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PNW
Usually there's a big volume between the ADD and FULL marks on a dipstick, like at least 1 quart on most engines. So 5-6% expansion (if that is accurate) is insignificant. If that much difference could/does cause problems in your engine, it needs repair of some kind. Just keep the oil level between the marks and find something else to worry about. Personally I've never seen much of a difference on a dipstick between cold and full temp.

Here's the dipstick in the 2nd Gen Coyote. The distance between the top hashed area line (full cold) and the top hole (full hot) is 23% higher on the dipstick (going by distance). Of course this will vary with every engine due to the shape of the oil pan.

S550 Mustang Dipstick.JPG
 
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391
Location
MD
Usually there's a big volume between the ADD and FULL marks on a dipstick, like at least 1 quart on most engines. So 5-6% expansion (if that is accurate) is insignificant. If that much difference could/does cause problems in your engine, it needs repair of some kind. Just keep the oil level between the marks and find something else to worry about. Personally I've never seen much of a difference on a dipstick between cold and full temp.
Not even ATF fluid moves up that much when fully warmed up.
 
Now consider that most the oil is contained in a rather small sump and that sump extends below the main part of the oil pan. The dipstick is extended down into the sump but the top of the oil is across the large cross section of the oil pan. The 6 % rise in volume would cause a rise on the dipstick. The rise on the dipstick would look exaggerated because it is sloping. It all depends on the design of the pan and how much oil is in the pan. :) To worry about it would be really anal.
 
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Danh

Thread starter
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1,993
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Not quite clear on your objective here, could you expound and clarify.

Best approach to what specifically?

As noted, this subject is definitely “in the weeds”. But here’s my example: the stated refill capacity of one of Honda K24Ws Is 4.4 quarts. When I add this amount, run the engine and check the following morning, I note it’s typically not at the “full” line. The temptation (to which I succumb) is to top it up to that level. Checking the oil after a long Interstate run then shows the level at about 1/4 quart over full.

Honda K24Ws are DI engines and I initially suspect fuel dilution was the cause, which is why I stumbled down this particular rabbit hole.

So the question was, should I fill to full cold and accept a slight overfill on a hot engine or accept a slight underfill cold for a full reading when hot. And the answer, almost assuredly, is 1/4 quart doesn’t matter in the least and either method is OK. My point in raising this was really to confirm my understanding of volume vs temperature of fluids was correct, if not all that relevant.
 
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838
Location
NJ, USA
From the FTC's weights and measure statutes:
l. REQUIREMENTS FOR MEASURING THE ACTUAL CONTENTS OF PACKAGES
1.1 The actual contents of packages may be measured directly by means of weighing instruments or volumetric instruments or, in the case of liquids, indirectly, by weighing the packed product and measuring its density.
1.2 In all operations for checking quantities of products expressed in units of volume, the value employed for the actual contents shall be measured at or corrected to a temperature of 20°C, whatever the temperature at which packaging or checking is carried out. However this rule shall not apply to deep frozen or frozen products the quantity of which is expressed in units of volume.

20°C
 
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1,967
Location
USA
So the question was, should I fill to full cold and accept a slight overfill on a hot engine or accept a slight underfill cold for a full reading when hot. And the answer, almost assuredly, is 1/4 quart doesn’t matter in the least and either method is OK. My point in raising this was really to confirm my understanding of volume vs temperature of fluids was correct, if not all that relevant.

Assuming a properly engineered machine and properly sized sump for all operating envelopes......

In terms of the mechanical functioning and tribology of a machine, anything over the fluid volume requirements doesn't and cannot hurt at all. ( the machine doesn't care if the oil intake sucks from a quart can or million gallon tank as long as the supply is never starved)

The question then gets changed to "Is the physical volume of the sump going to create a different problem elsewhere?" such as aeration from plunging, overflow etc. ( that's more machine specific)

Honda K24Ws are DI engines and I initially suspect fuel dilution was the cause, which is why I stumbled down this particular rabbit hole.

That's really a different issue because if dilution is happening, that's an additional volume being added and has no bearing on expansion at that point.
 
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