Why do you have to have the engine running to check the transmission fluid level? The transmission has a pan like the engine, so I was wondering why the vehicle has to be running to check the trans fluid, but not for engine oil? thanks
Check Trans Fluid with Engine Running?
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Is this now common practice correct in every case, or are there not vehicles where the transmission fluid level is checked cold and level?
An additional question is why there is not an accessible capped reservoir for ATF. Somethin' "dry-sumpish"?
Heat, maybe?
An additional question is why there is not an accessible capped reservoir for ATF. Somethin' "dry-sumpish"?
Heat, maybe?
My guess is that the reason for having the car running is to eliminate 'variables'...in other words they know that a 'running' transmission will have a consistent, repeatable level of fluid in the different parts of the unit. If not running, you could have different amounts of fluid in the various parts of the transmission / pan, which could skew the results.
Same thought pattern applies to why (on some transmissions) you have to shift through all the gears (PRNDL2) before taking the reading.
Just my $0.02
Same thought pattern applies to why (on some transmissions) you have to shift through all the gears (PRNDL2) before taking the reading.
Just my $0.02
Hondas, at least in prior generation automatics, specified checking ATF level with the engine off. Everyone else, so far as I'm aware, specifies checking with the engine running. As I understand it, the reason for rowing through the various gear ranges is to bring fluid into all areas of the valve body and the transmission. The dipstick is calibrated to read accurately only in this condition.
MolaKule
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For most cars with an automatic transmission, the torque converter holds quite a bit of fluid and it's fluid level is "above" the level of the sump, so it needs checking while engine is running and fluid is being pumped around the transmission system. The fluid is being sucked out of the sump and ciculated through the Torque converter, the valving, and through the cooling system. At engine off, the fluid from the Torque Converter drains back into the sump and runs high up on the stick.
If the torque converter system is at or below the level of the sump, then it could be checked while the engine is stopped.
In either case, the dipstick is calibrated for the type of system.
The owner's or shop manual should tell which is the proper method for your daily driver.
The manual for my 1998 Jeep Grand Cherokee Laredo I6 calls for checking the fluid while the transmission is in Nuetral after shifting through all the gears.....go figure.
The AW-4 trans pumps in NEUTRAL (and the reverse/drive positions), but not in PARK. This is the same reason the manual tells us to shift to NEUTRAL at a complete stop when pulling a load; after a a heavily-loaded highway run with AC on; when engine cooling light comes on. ATF fluid needs all the cooling help it can get, and motor runs more freely.
(And is another good reason on a very hot day to -- after a long heavy high speed run -- to let vehicle stand [to one side] in NEUTRAL, brake on, hood up and rpms up to around 15-1900 to allow rapid cooling prior to shutdown. This can help avoid heat spikes in motor/trans systems when fluids are no longer circulating).
Same as in the old Chrysler 727 or some of its modern variants.
I pause for a three-count in each trans position (after a 7-15 mile warmup), parking brake on fully.
I check them when hot after a good highway run, especially if the fluid level is suspect or has been recently adjusted. (What "looks" like only a small amount over or under can often be nearly a quart, or even significantly over).
(Very nicely put, Molakule. Best short description I've read).
(And is another good reason on a very hot day to -- after a long heavy high speed run -- to let vehicle stand [to one side] in NEUTRAL, brake on, hood up and rpms up to around 15-1900 to allow rapid cooling prior to shutdown. This can help avoid heat spikes in motor/trans systems when fluids are no longer circulating).
Same as in the old Chrysler 727 or some of its modern variants.
I pause for a three-count in each trans position (after a 7-15 mile warmup), parking brake on fully.
I check them when hot after a good highway run, especially if the fluid level is suspect or has been recently adjusted. (What "looks" like only a small amount over or under can often be nearly a quart, or even significantly over).
(Very nicely put, Molakule. Best short description I've read).
thanks for the replys. Makes sense now after molekules description, but I don't know why the manufacturers could not just figure out how much transmission fluid should be in the sump after ther TC drained to make it easier just like you have to wait for engine oil to drain back into the sump before you check it. Seems like they could be checked to same way, but oh well, atleast i now know why the engine has to be running to check the trans. Thanks again
Also, ATF expands as it reaches operating temperatures.
I have an old GM factory assembly manual around her somewhere that explains procedures for adding fluid cold to a new trans so it will be at the proper level with hot.
I have an old GM factory assembly manual around her somewhere that explains procedures for adding fluid cold to a new trans so it will be at the proper level with hot.
Because of one BIG variable - as in "how long" after shutdown. By specifying that a fluid level check be done at operating temperature with motor running, the results will be more consistent for comparisons. As Mike stated above, fluid expansion volume at operating temperature will also elliminate the level variability that would result form a cold check at, say 50 degrees F. compared to another done at, say 95 degrees F. Some car makers provide dual calibrations on their ATF dipstics for both cold and hot readings, but they inevitably recommend that doing the check when at operating temperature is more accurate. At least be glad you can check the ATF level on your car's trannie. Some GM transmissions (others, too?) have neither a dipstick nor any convenient means to top-up or refill.
I always checked my Honda Accord AT with engine running, PRD21, on level ground, 25 mile drive and it was a the full mark. After I shut off the engine, it go 1/4in higher than full mark. If I put on full mark on it with out the eninge running, it got on low mark with the engine running! So confused!
Did I overfill my trans?
Honda sucks as I learn more in this board:
Specific PS fluid. A lot people did not know!
SOHC
Belt type timing belt.
Interference type (if belt broke, you say bye bye)
Stupid way to check ATF.
Plastic windows rail (or whatever it called).
"Hic kup" trans type.
Never buy a Honda again!
When I bought my 93 Caprice, it had 113k on it. At 115k, I had the transmission fluid flushed on one of those machines. The filter was not changed. I have 206k now and have not added any. I have never been able to really tell what the level was on the dipstick, though. Even after several attempts at wiping the stick down, there is still plenty of fluid way above the add mark. So I *think* the level is fine, and it's gotten me almost 100k. The filter probably has 145k on it. Should I be worried?
100k on the fluid yes you should be worried, way beyond time to change it. Schuduled intervals are 20-30k miles, with filter done every other flush.
As has been said, the dipstick is calibrated for its check, but at operating temp, after being ran through gears is ideal. Reason being is this is how the fluid is when your driving--its where its need and not nesscarily in the pan.
No matter how well the dipstick is calibrated if maker designed to be check with engine off an cool they forgot about one key element--ambient temp. For here in the states have temperature range of -60*F to 120*F and if you think it would read the same at those temps your are sadly mistaken.
As has been said, the dipstick is calibrated for its check, but at operating temp, after being ran through gears is ideal. Reason being is this is how the fluid is when your driving--its where its need and not nesscarily in the pan.
No matter how well the dipstick is calibrated if maker designed to be check with engine off an cool they forgot about one key element--ambient temp. For here in the states have temperature range of -60*F to 120*F and if you think it would read the same at those temps your are sadly mistaken.
Not to mention I've been hard on the car since I got it. Full throttle upshifts and downshifts, top speed runs, etc. All things considered, that 4L60 has been remarkably solid.
You can tell how good the ATFis;
Fresh fluid is translucent and cherry red. Some darkening is normal, but if it is reddish brown or mustard color and smells like burnt varnish, it is worn out. Maybe it can flushed and all is OK but its something that can also point to trans problems looming on the horizon.
Fresh fluid is translucent and cherry red. Some darkening is normal, but if it is reddish brown or mustard color and smells like burnt varnish, it is worn out. Maybe it can flushed and all is OK but its something that can also point to trans problems looming on the horizon.
I'd be happy to take that crappy Honda off your hands for a reasonable price, of course
Checking ATF level is vehicle specific.
Read your owners manual.
Level surface is a must. Hot or cold, running engine or not, depends on the model.
Why? because thats what the engineer wanted.
Be glad you have a dipstick and a place to topoff the ATF. Some cars don't!
Read your owners manual.
Level surface is a must. Hot or cold, running engine or not, depends on the model.
Why? because thats what the engineer wanted.
Be glad you have a dipstick and a place to topoff the ATF. Some cars don't!
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