I bought my van used. At the time the seller changed the automatic transmission fluid. Like any good fool I trusted it was done correctly ... to the extent of not looking at the dip stick marks.

Recently I was doing an overall fluid check and found the Automatic transmission fluid was high. Turns out there was about 5 cups too much auto-trans fluid in the transmission. Yes I know ... how in the world could I not notice that? ... my only excuse is I had some strange idea the fluid change was done correctly and had previously only checked to see if it was lower down on the stick.

I see from some searching that the primary result of overfilling an automatic transmission is that the fluid may foam or be forced out of the dip stick supply tube or overheat. There is mention of the transmission kicking between gears if the fluid is low. There are also mentions of "newer, more tightly engineered" transmissions needing the fluid level to be exacting.

I've put almost 7 thousand miles of easy driving on the van since I bought it and I assume that if damage was done it is done and beyond any remedy. Please correct me if that is not the case.

Oddly, the transmission has operated extremely well ... meaning it is very smooth between gears. The only time it kicks a bit is when the van is parked on a hill and I shift from Park into a gear. After draining down the fluid I notice no difference in the operation during in-town driving.

I had test driven a new van and a not as old van prior to purchasing the one I have and they both kicked between gears. No one at the time could explain why the transmission was so smooth.

A "mechanic" had overfilled my other vehicles differential fluid and the oil leaked out the seals until I drained it down to the correct level. I'm really surprised there have been no signs of the over filled auto-trans fluid.

- So what really happens when the transmission has too much fluid (oil) in it?
- Is the only sign of over heated transmission fluid a darker color?
- And why is checking the auto-trans fluid so different from checking the engine oil?

 

what temp was the fluid at when you checked it.

 

"Oddly, the transmission has operated extremely well ... meaning it is very smooth between gears. The only time it kicks a bit is when the van is parked on a hill and I shift from Park into a gear. After draining down the fluid I notice no difference in the operation during in-town driving."



I always put on the parking brake fully before taking my foot off the brake in park on a hill. That way the van isn't sitting on the parking pin, but the brakes instead. If your parking brakes allow the van to move downhill, then they need adjusting.

 

5 cups on a 6 1/2 quart capacity is not really that much in my mind. I would not expect there to be any damage.
Overheated tranny fluid will smell as well as have the dark fluid.
It is only different in that there is a set procedure to check tranny fluid, and the engine needs to be running, unlike when checking engine oil...

 

Yep it will read higher if you check it turned off and cold. Warm engine, running in park or neutral, check diptstick.

I always teach this procedure to my employees parking on hills, esp with a loaded van:

1. Shift into neutral, right foot on brake, engage parking brake.
2. release foot brake, let weight "settle" on parking brakes.
3. shift into park.
4. when leaving.. left foot on brake
5. shift into drive, release parking brake
6. right foot on gas, release left foot on brake.

 

Thank you for the responses.

I have done the ATF check based on the manual.

I also found the following website with ATF color and smell conditions to better judge the condition of the ATF.

What Can You Learn from The Color And Smell of Automatic Transmission fluid?

At this point the fluid is between clean and slightly brown. There is no smell and not shifting symptoms. I've got my fingers crossed that the pervious owner just did a drain and refill ... and have a call in to find out what the "not to distant future" means for full clean and filter replacement.

Does anyone have feed back on ATF fluid manufacturers?
I made a call to the local GM parts dealer and was told Decron ATF numbers play forward but not backward ... meaning Decron 3 can use 4, 5, 6 but 6 can not use 5 and below.

 

the most accurate way to check fluid level is with the trans fluid hot. the dipstick should be hot to touch. the cold and hot fluid level marks on these dipsticks are very far apart on these dipsticks. So was it over the full hot mark or full cold mark?


you will get a clunk from any trans when you park on a hill without using the parking brake. its the parking pawl torque locked.


best option is to use dexron fluid as it has the friction co-efficients designed exactly for gm trans. aftermarket fluids are designed to meet everything under the sun.