# Thermal Coefficient of Expansion of Engine Oil

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#### nhzero

Does anyone know the thermal coefficient of expansion of engine oil? I need it for a speech, and I can't find it by Googling. Thanks!

Just for chuckles, I'm going to make a guess here. Maybe someone will have a hard answer and we'll see how close I am. I've noticed that if the oil level in my car is right on the one quart low mark when it's cold, it rises to almost, but not quite, a quarter quart when hot. I.E. 4 quarts to 4.2 quarts. Let's say the temperature difference is equal to ambient to the operating temperature of the engine coolant. I.E. 20C to 100C. 4.2 / 4 = 1.05 I.E. 5% volumetric expansion 100 - 20 = 80C delta T 5% / 80C = .0625%/degree C So, my rough estimate would be on the order of .06% volume per degree Centigrade.

0.00088/K with a density (rho) of 870 kg/m^3

This is for petroleum (density=.8467). Coef of Exp. =.000955 at Temp= 20 C

Rick, well done, you got within a poofteenth of the answer using observation.

quote:
Originally posted by Rick in PA: So, my rough estimate would be on the order of .06% volume per degree Centigrade.
Ah, the coefficient is in terms where 1.00 = 100%. Shift the zero two places on my rough estimate (to get rid of the %) and you get an estimated coefficient of .0006/C. [ January 26, 2003, 09:35 PM: Message edited by: Rick in PA ]

uhh... about 1/8th of an inch up the dipstick?? is there a reason why you need to know this?

THANKS!!! I needed to know for a demonstration speech where I am showing how important it is to check your oil when it is hot instead of cold, but being an engineering student, I can't just spout off theories without numbers. Thanks again!!

nhzero I have a question maybe it can be verified by you? Some old timers and those who were worked in the military depot as mechanics have strongly suggested to me that I should keep my oil between the min and max marks. Because oil through heat allows for thermal expansion of the oil's properties this in turn would prevent additional wear on the motor and less stress on the seals in the motor in many cases preventing leakes, Is such and explanation a fallacy or is there credence to this?

I prefer to check it cold since manufacturers allow for expansion.

Consistency should rule. I check a few minutes after hot shutdown but whatever works based on accuracy of dipstick, original fill level, added capacity, etc. Depends on the vehicle, but it'll often read about the same cold, I assume because of more thorough drainage. Has anyone thought about adjusting the fill level based on geography? Wouldn't a hilly area promote foaming in an otherwise "very full" pan? (Patman, this one's for you. ) David

Hehe, as if I don't have enough on my mind to worry about David, then you have to throw that into the mix! I seriously think that my method of checking my LT1 cold is not the right way to go. If I had trusted it this weekend, I would've added another 100ml of oil, after adding 200ml of oil the previous weekend, only 3-400 miles prior. There is no way I lost that much oil in a week. So if I kept adding oil thinking it was low when it was not, eventually I'd have been overfilled. I think that with the engine cold, in extreme cold weather like we're having here (it was -9F this morning!) the dipstick readings will be way off. In the summertime I think I could probably check it either way and not see as much varience though.

quote:
Originally posted by MolaKule: I prefer to check it cold since manufacturers allow for expansion.
I could really tell the properties of expansion on my BMW bike, since there is a sight glass, I put it on the stand hot, then when it cools it would be down about 1/4 inch on the glass. Pretty neat. Anyway I kept my oil within 1-2 oz all the time, so I could tell if it was using oil.

Someone previously mentioned that it should be checked hot, or at least warm because over time the filter will drain. Consequently reading a too high level. If this is true, the reading certainly won't be accurate. Yes most filters have ADBV, but not all seal 100%. And how do you now which you have?

http://news.google.com/newspapers?nid=1350&dat=20020725&id=Px0VAAAAIBAJ&sjid=5QMEAAAAIBAJ&pg=6788,2706616 For anyone still interested, here's a link from Click and Clack where they tested and it didn't make any difference when they tested it - warm or cold.

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