Checking tranny fluid...
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Cargo Master
Joined: Jul 2009
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From: Des Moines
Checking tranny fluid...
Can someone please explain to me why it is that the engine has to be running to check tranny fluid? I get that the engine turns the main shaft of the tranny, and this is circulating the fluid, buy why is this necessary? I'm just asking because I'm thinking about marking my dipstick with the engine off and using that as a reference.
Post Fiend
Joined: Jan 2005
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With the engine running the front pump fills the torque converter (if needed) and servos and valve body with fluid.
With engine off fluid may drain back in varying amounts depending on how long it has been not running and condition of check valves.
With engine off fluid may drain back in varying amounts depending on how long it has been not running and condition of check valves.
Junior User
Joined: Apr 2011
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pump also fills the trans cooler in the front which has lines that hold fluid so all of the above and the trans cooler and the lines contain fluid so they have to be full before you will get an acurate reading on the dipstick. the dipstick should read high when the engine is not running
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Cargo Master
Joined: Jul 2009
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From: Des Moines
Okay. So, theoretically speaking, if one was to make positively sure that the tranny fluid was at the correct level, he could mark the dipstick w/ the engine off and use that as a reference. Theoretically... 
Lead Driver
Joined: Feb 2002
Posts: 7,955
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From: Greater Austin, Texas
I used to check new cars (Chevies) during make-ready with the engine off, I just knew from experience where the level should be. But this was on brand-new transmissions which theoritically would have very little bleed-down. I don't do it on older vehicles because of the variables mentioned above.
