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How Much Does ATF Expand With Heat? #5238406 10/13/19 09:42 AM
Joined: Mar 2019
Posts: 8
Whalstib Offline OP
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I always wondered why ATF must be checked at a certain temperature range and figure it must expand quite a bit. Old dip stick method had a ~2" of variance. My new Tundra uses the "open valve" method like a differential but needs to be in a specific temperature range that makes it a PITA compared to dip stick although more accurate..

So if I have a 15 qt capacity how much would it measure at 50°F vs 120° F ? As temperature rises does it expand more? Does it even expand or need to be thin enough to fully immerse all the little ports and be flowing fully?


Re: How Much Does ATF Expand With Heat? [Re: Whalstib] #5238441 10/13/19 10:21 AM
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hallstevenson Offline
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I can only relate my experience and it's this: On 3 separate occasions, I drained between 3.5 and 4 quarts of ATF from two different vehicles. Did this while the ATF was "hot", in excess of 150º F (after a good 30 minute drive). Poured it into a container and marked the level. Using an infrared thermometer and waiting close to an hour, it eventually dropped to around 75-80º F and for all practical purposes, the level did not change. Certainly not enough to visually notice.

Re: How Much Does ATF Expand With Heat? [Re: Whalstib] #5238454 10/13/19 10:43 AM
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demarpaint Offline
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Here's a picture for the NAG 1 transmission fluid level graph. You can get an idea of how much the ATF used for that unit [ATF+4] expands and take an educated guess based on that. [Linked Image]

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Re: How Much Does ATF Expand With Heat? [Re: Whalstib] #5238455 10/13/19 10:48 AM
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simple_gifts Offline
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Of course the container it is held in is also expanding or contracting... grin2

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Re: How Much Does ATF Expand With Heat? [Re: Whalstib] #5238466 10/13/19 11:18 AM
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spk2000 Offline
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Quote below hope it helps:



Coefficient of thermal expansion for oils and transmission fluids is around 0.0007 per degree C (0.07%/C). So, if you've got 12 liters in the pan, it will expand 0.0084 L per degree C. Since there's increased volume, and the surface area of the fluid does not change appreciably, the fluid goes higher on the dipstick.

Volume = Area x Height. So, Height = Volume/Area. Therefore, height on the dipstick is proportional to volume change.

Summer time temperature change might be ambient air temperature 68F (20C), at start up, to around 180F(82C) at operating temperature. Or, around 62C.

Therefore, during the summertime, the fluid could be expected to expand 0.0007 x 62C = 0.0434 (4.3%).

Last edited by MolaKule; 10/13/19 07:57 PM.

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