Oil Volume vs Temperature

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If owned a car that had a fuel dilution issue I would fill the oil to a bit below the full mark at each oil change, to allow for a rising oil level due to the fuel dilution. How much below the full mark would depend on how bad the fuel dilution issue was.

I haven't seen a fuel dilution problem on my particular cars, so I make sure that the cold oil level is never above the full mark, and don't worry about the hot oil level being a bit above that.
 
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The coefficient of expansion of motor oil is 0.00039 per degree F. If you took one gallon of motor oil at 70 F and heated it to 220 F, the temp rise is 150 degrees F. Multiply 150 by 0.00039 and add that to 1. That 1 gallon would now be 1.06 gallons.

Is that 0.00039 factor an oil-specific value? Or what exactly? I'd assume the lighter the oil the more it expands?
 
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Say your engine holds 6 quarts. You buy 6 quarts of oil. By looking at the markings on the container (s), it looks like, yes, that's 6 quarts. Pour it in. Good. Now you have 6 quarts in the engine. It's happy. Cold or hot, that little old 1/4" doesn't matter.
 

ZeeOSix

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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.

I've done it both ways and it doesn't really matter. An engine isn't going to have any negative ramifications if the oil level is on the "full" mark on the dipstick when the oil is cold. Pretty much all the owner's manuals I've read say to check the oil level when hot, so "technically" they want the oil level no higher than the "full" mark when hot. But it really isn't going to matter.

When I change oil, I will fill the engine with a little less than what it takes. Then drive it around for 5 miles, go home and let it sit 15 minutes, then check the level hot. Add oil to get the level right on the "full" mark when hot. A bit more tedious, but it gets the level to the "full" line when hot and establishes the hot level baseline. I then check it cold the next morning and make note of where the cold level is because I typically like checking the oil when cold since it's easier to read the dipstick.
 
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Say your engine holds 6 quarts. You buy 6 quarts of oil. By looking at the markings on the container (s), it looks like, yes, that's 6 quarts. Pour it in. Good. Now you have 6 quarts in the engine. It's happy. Cold or hot, that little old 1/4" doesn't matter.
This.
 
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From the FTC's weights and measure statutes:
The actual contents of packages may be measured directly by means of weighing instruments...

At the old Pennzoil canning plant just outside Oil City, PA, drums were placed on a scale and filled. The oil was generally much warmer than ambient temperature, so filling by weight guaranteed accuracy.
Those guys could handle a 450 lb drum with each hand with little effort. Two at a time, that was pretty remarkable.
 
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Say your engine holds 6 quarts. You buy 6 quarts of oil. By looking at the markings on the container (s), it looks like, yes, that's 6 quarts. Pour it in. Good. Now you have 6 quarts in the engine. It's happy. Cold or hot, that little old 1/4" doesn't matter.
That's the right idea. To be more general, just pour in the specified capacity, whatever that is. Then run the engine a bit, and check the dipstick at whatever temperature (and any other conditions) you prefer. There's your correct reference level.

Some people like to make simple issues complicated!
 

Danh

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That's the right idea. To be more general, just pour in the specified capacity, whatever that is. Then run the engine a bit, and check the dipstick at whatever temperature (and any other conditions) you prefer. There's your correct reference level.

Some people like to make simple issues complicated!

Be nice. I acknowledged this issue was more one of theory than of any practical importance. Let’s not discourage discussion.
 
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This thread is proof of all the OCD running rampant on BITOG. Pure insanity.
Too many people topping off when the level is 2mm below the full mark. More insanity.
On a healthy engine in normal usage, anywhere between the marks is a good oil level.
 

Danh

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This thread is proof of all the OCD running rampant on BITOG. Pure insanity.
Too many people topping off when the level is 2mm below the full mark. More insanity.
On a healthy engine in normal usage, anywhere between the marks is a good oil level.

Thank you. Perhaps you should find a forum that mets your standards.

Sincerely,
OP
 
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When I check it hot, it's a usually a bit down. When I let it sit overnight, it's where I expect it to be.
 

ZeeOSix

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When I check it hot, it's a usually a bit down. When I let it sit overnight, it's where I expect it to be.
How long are you waiting for a hot check? Every vehicle I've ever owned had a higher oil level when hot vs cold.
 
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