Checking Transmission Fluid Level (Applies to all cars)

[Guest ZombyWoof]

Perhaps I'm missing something obvious, but...

Why do you have to check the level of your transmission fluid with the engine running and hot?

Can't there be a "cold and not running" level on the dipstick?

ZW

[Bill Stoneberg]

I think it was designated that way because if your car sits for awhile the fluid will drain out of the torque converter and into the pan. You would then show too full.

So to decrease the errors and make sure the tranny is full, you check it while it is warm and running.

[NTX5467]

Bill's correct about the "non-running" fluid level. There's usually a check valve to keep the torque converter from draining completely after the vehicle sits, but some of it will drain back anyway, plus run out of the valve body, too. The ONLY way to gauge that would be to first have the fluid level "to spec" and then let it sit continuously for a few days and check it before you start the engine. You'll probably see the level waaayyyy up on the stick, though, but it might NOT have a real correlation to the actual fluid level when the engine is running.

In the assembly manual for a '71 Camaro, it mentions that the "dot" below the add mark is where the fluid level should be (when the vehicle is "cold" and the engine running, as in approx 0 degrees F. temperature), as the "lower 'ADD' mark", so to speak.

Another thing to consider is that ATF fluid temp will not match engine coolant temperature until after several miles of driving with the engine fully warmed up--not just as the thermostat has openned. Therefore, I believe you'll need to drive the car about 5 miles after the engine temp is up to get a true measure of the ATF level in the trans.

Read your owner's manual as to the correct procedure to check the fluid--whether in "Park" or "Neutral" at hot, base idle. Also, the "Hot" level is fine if it's somewhere near, but below" the "Full" mark--or in the "Operating Range" area. Key thing is that it's not significantly above the "Full" mark and has no great amount of air bubbles in the fluid on the dipstick--when the transmission is fully at operating temperature. If you get it too full and then do some things that will make it get hotter (i.e., trailer towing or "high perf driving"), then it might upchuck fluid out the filler tube or the case vent.

Once you get everything figured out, it's not that hard to check the fluid the correct way.

If, per chance, the vehicle's hood might be a little close to the trans dipstick tube, you might need to exercise a little caution to not bend the dipstick too much as you get it started into the tube. Some GM trans dipsticks had a "separated" area near the lower tip, which was supposed to be something of an additional indicator of how low the fluid level might be (I guess), below "Add". If that area gets bent too far too many times, it'll break. So try to ease the approach of the dipstick into the tube and let the more solid parts of the middle of the dipstick do the bending rather than the tip end.

Just some thoughts,

NTX5467