Why check Transmission Fluid while engine running?


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Old 05-24-10, 08:35 AM
G
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Why check Transmission Fluid while engine running?

Hi all,
Saw another thread about performing a check while engine running and wanted to ask why you always have to check the transmission fluid while the engine is running?

Though, I always check according to those directions, I've never really understood Why? It would seem a static check, if you noted where the fluid comes up on the T-fluid dipstick would reveal, consistently the same fluid level if there were no leaks.
It occurred to me that the only way it would change significantly (other than a leak...) would be if the T-fluid wasn't being distributed to where it needs to be in the transmission - and hence, you'd read 'more' fluid than should-be upto the 'FULL' level.
Maybe someone that has experienced related tranny problems could give some better insight on type of problems you can see from the T-dipstick...
Thanks,
Greynold99
 
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Old 05-24-10, 09:59 AM
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"It occurred to me that the only way it would change significantly (other than a leak...) would be if the T-fluid wasn't being distributed to where it needs to be in the transmission - and hence, you'd read 'more' fluid than should-be upto the 'FULL' level"

I thank you answered your own question-----
This is the reason the engine needs to be running and at operating temperature. The torque converter will "bleed down" a certain amount when the vehicle has been setting and cooled off. This will naturally raise the fluid level.
 
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Old 05-24-10, 10:23 AM
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Reply to Giles

Thanks Giles...
Could I ask a follow-up question since I've never had a transmission problem related to the fluid level being too low or high...?
If you had the situation you describe as a problem, i.e. the T-fluid being too high when checking as you describe because it wasn't sufficiently being drawn down by the Torque Converter - does it stand to reason that you'd start to have or already have other physical issues such as the transmission drive fluctuating while driving or losing power when you accelerate no matter how much you step on the accelerator?
I mean by the time you get a negative reading on the T-fluid dipstick, is it generally too late -- that is excluding fluid leak?
Thanks again,
Greynold99
 
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Old 05-24-10, 10:43 AM
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First--the TQ doesn't draw fluid, fluid is pumped into the converter under pressure from the transmission pump. This is accomplished in just a few seconds and if it isn't filled properly, you won't go far.

In crude layman terms--The TQ works on the principal of fluid resistance. If you were to place two fans toward each other and only one was turned on., wind turblance would turn the other fan. Now--If you were to enclose their blade in a sealed housing and fill with fluid, you can see how the turblance would be increased.
 
  #5  
Old 05-31-10, 10:40 PM
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trans fluid check

They could have made them to check with the engine off but you would have to wait until you were sure the fluid had all drained back. This way you can check it anytime. Just an aside some big engines you check with them running. Dont know the reasoning behind this one. I ran a 2000 series Cat that was this way,it held 18 gal of oil.
 
 

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