Overfilling ATF Fluid/Underfilling

[mareakin]

How much tolerance do you think modern automatic-transmissions have for underfilling and overfilling?


Why do I ask? Well, after doing a drain/refill, I may have underfilled it by .25Quarts and upon finding this out, I think I overfilled it by .25 quarts.... heheeh

It seems with trannys, there is much less tolerance than Engine oil.

And measuring the amount can be a pain in the butt, amirite??

You have to satisfy certain conditions such as hotness or whatever.

 

[mareakin]

I guess I'll use a tube and suck a little bit out and then measure again.

and, if i've sucked too much out, I'll have to fill it in again.

 

[nwjones18]

If your worried about it sucking it out is the only way to go. I've never had, or heard of, any problems from being overfilled by a .25 quart.

 

[SteveSRT8]

most trans have an overflow tube or vent.

In the old days many a trans shop simply packed them tightly full of fluid and let the excess blow out!

Now I have to use a scan tool and know the fluid temp to use a graduated scale in mm to check the level!!!

 

[JHZR2]

I can never get a good read of ATF on the dipstick in any car. Not sure why. Im sure .25 is easily done due to difficulty in reading and is likely OK. The key is no bubbles/foam IMO.

 

[StevieC]

My Trans is always overfilled because it shows proper at the cold level but will be way over the hot level. I have tried filling to the proper hot level and then it will be low on the cold level.

I gave up and figured if it's good cold and over full hot that is better as long as there is no erratic shifting and no foaming or aeration can be seen in the oil.

I haven't had any issues with this process in my transmission.

 

[scurvy]

Originally Posted By: mareakin
How much tolerance do you think modern automatic-transmissions have for underfilling and overfilling?

Plenty. Overfilling a bit is always better than underfilling a bit.

Originally Posted By: StevieC
I gave up and figured if it's good cold and over full hot that is better as long as there is no erratic shifting and no foaming or aeration can be seen in the oil.

I support this plan.

This is also what I do with my engine oil, which causes people on TDIClub to get their panties in a wad that my oil could be a millimeter over the 'full' mark when hot. It's my dang car, and I'm happy with the oil 3cm over the full mark when hot.

 

[StevieC]

I always overfill my engine oil by at least a half a liter because of possible dipstick mis-marking and because I would rather have that extra bit in the engine should I be turning a steep corner or parked sideways on a hill etc. so as to not cause oil starvation.

It's 2-3 litres over that's a problem IMO. This logic has never failed me yet.

 

[meep]

some newer cars are picky. mine is another read-the-temp-see-the-chart-measure-in-mm PITA. I change it by sucking out 4 qts, dumping in 4 qts...

Mike

 

[jtaylor]

When I do drain and fills on my Honda, I measure how much drains out, then I put that much back in. pretty failsafe.

 

[scurvy]

Originally Posted By: jtaylor
When I do drain and fills on my Honda, I measure how much drains out, then I put that much back in. pretty failsafe.
Assuming it was filled correctly the first time and you can measure accurately, yes.

 

[ctrcbob]

I hate these transmissions that DO NOT use a dip stick. My Genesis is like that, using the ZF 6 speed, the same transmission used on many Jaguars and some Mercedes. The instructions for both my Genesis and Jaguar is that you check the level from the fill plug, with the fluid at a certain temperature. Somewhere around 40C. The temperature of the fluid is checked by plugging in under the dash. At the correct temp, if level is low, you fill until it overlows out the plug hole. If level is high, you allow it to drain out unit it stops.

I have a friend with a Jag XJ8 who had a garage change out his fluid with M1 ATF. NOT flush, but fill, run, drain, refill, run, drain, fill a third time. After the third time, they read the temperature of the fluid with a probe stuck into the fluid at the fill plug. BTW, he is very happy the way the ZF 6 Speed operates with the M1 ATF.

I change my Continental fluid with the "Pump & Fill" method. Pump out to a measured container, from the dip stick tube, then fill with new fluid, the same amount that was pumped out. Then drive car and check level after a short drive, and perhaps the next day, after a longer drive.

 

[AlphaMale8]

I found this thread on a search, and I'm glad to read that others find the same thing I find after an ATF change in that it gets overfilled a bit once the tranny runs to operating temp.

My level reads a bit over full at the HOT scale, but the tranny shifts normal, so I think I'm just gonna leave it be unless I notice something weird.

I didn't know that ATF overflow tube could prevent overfilling - awesome!

 

[cmf]

Originally Posted By: AlphaMale8
I found this thread on a search, and I'm glad to read that others find the same thing I find after an ATF change in that it gets overfilled a bit once the tranny runs to operating temp.

My level reads a bit over full at the HOT scale, but the tranny shifts normal, so I think I'm just gonna leave it be unless I notice something weird.

I didn't know that ATF overflow tube could prevent overfilling - awesome!


I don't think I'd want to rely on a trans overflow tube blowing ATF all over to properly fill my transmission. There was also a case of an overfilled transmission shooting the ATF out of the fill hole and it ignited on the catalytic convertor and set the engine on fire, although that is a rare scenario.

The proper technique for measuring ATF is to drive the car until the ATF heats up to operating temperature and then use the dipstick to see if it's within range. A lot of cars also require you to be idling the car in Park or Neutral, check your owners manual.

An overfilled transmission can cause the aeration of the fluid which will lead to poor operation, increased temperatures, increased wear. But with that being said, if it's only a bit over full when hot, then it's fine, transmission probably wont even notice.