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Old 08-17-2014, 06:27 AM
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Basic ATF Thermal Expansion Question

I know that ATF level is very sensitive to fluid temperature....my understanding was that that was due to the thermal expansion of the fluid. Yet I notice that the HOT ATF that I extract is at the same level in the extractor the next morning when it's COLD....i.e. it doesn't seem to contract. What am I missing? What accounts for the difference in level if not the actual volume of the fluid?

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Old 08-17-2014, 08:57 AM
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Quote:
Originally Posted by shertex View Post
I know that ATF level is very sensitive to fluid temperature....my understanding was that that was due to the thermal expansion of the fluid. Yet I notice that the HOT ATF that I extract is at the same level in the extractor the next morning when it's COLD....i.e. it doesn't seem to contract. What am I missing? What accounts for the difference in level if not the actual volume of the fluid?
Over night you get an air pocket in the torque converter. That is why you check it when it is running & warm.
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Old 08-17-2014, 02:39 PM
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Originally Posted by layback40 View Post
Over night you get an air pocket in the torque converter. That is why you check it when it is running & warm.
No....the fluid that I'm talking about is no longer in the car....it's sitting in an extractor. The volume is the same whether hot or cold. So I'm wondering what is meant by the thermal expansion.
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Old 08-17-2014, 04:12 PM
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Is "hot" at ambient temp (+/-100F) sitting on the floor in your garage, or are you heating the stored fluid to equal actual 80C operating temp and then looking for the change in volume?

Going from 60F to 100F would be a minimal % increase temp and corresponding expansion.

If you are going from 60F to 80C that's an ~300% increase in temp.

To actually see the diff in expansion you'd probably need a sealed container with a small diameter clear tube that the fluid was forced to expand into. That would approximate what is happening inside your trans when fluid is measured cold vs hot.

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