Tran failure from overfill?

[NothinToSeeHere]

HI5-
Frequent reader here, few posts. I have been maintaining my vehicles and equipment for 50 plus years. I see frequent posts here about about transmission fluid level, the absurd methods to fill new transmissions properly - temp sensors, computer tools, etc.

I have been wondering - has any actually experienced a transmission failure due to fluid level being to high? It would seem to me the excess would purge through the breather tube?

thanks!

 

[pbm]

I've had several brand new cars come from the factory overfilled. My 1992 Sonata, my 2008 Corolla to name just 2.
Both were about half an inch over the 'full when hot' line. When I changed fluid I tried hard to get it perfect but
eventually realized that 1/2" over worked out to only about 6 ounces of fluid.....I stopped worrying about
being so exact after reading (I can't remember where) that slightly overfilling an A/T does no harm. Having said
that, I definitely would not overfill by a quart of ATF.....

PS: I'd rather be 6 ounces over than under filled...just my opinion....

 

[MaximaGuy]

I haven't ever read a tranny fail with high level or even low level - but I must say the transmissions misbehave when high.

 

[Pelican]

The problem of overfilling is twofold:
1) Additional internal pressure on everything as the fluid expands a lot when hot
2) Foam which does not lubricate and prevents the smooth flow of the fluid

 

[JC1]

My 98 Sienna was overfilled a few times. Never had an issue.

Maybe newer transmissions are more of an issue due to the programming and software that is part of the transmission design.

 

[mclasser]

Not failure, but I have experienced wonky shifting on several cars with overfilled ATF. If left like that for a long time, I wouldn't be surprised if damage would be done.

 

[matt36415]

Transmissions, even ‘sealed' ones have vent or breather holes. Having been a transmission tech for some years I have seen cars withfluid sprayed around the engine bay from completely filling a transmission but never a damaged one from too much fluid. The boxes just spit it out - no damaged seals etc. Just spray out of the dip stick and or vent holes

 

[Lubener]

Overfilling may not always flow out depending on how much it is over filled. The fluid can become foamy and cause slippage. Over time, things can start to fail.

 

[nascarnation]

A really big overfill can cause spewing out the breather or dipstick which can lead to a fire if the exhaust pipes/manifolds are close by. Rare but I've seen it happen in trucks.

The correct oil set line is below the rotating internal parts, so with a moderate overfill you can get aeration of the fluid and more heat buildup due to the parts whipping through the oil. Aerated oil causes variation in the controls, and as mentioned above harshness or slippage.

 

[01rangerxl]

I overfilled my 02 Ranger's 5R44E by about a quart. Drove it that way for a while, I don't remember how long. It had an occasional weird shift, but was fine. Fluid level was adjusted to the proper level 40K miles ago and it works great at 234K. No harm done in my case, but different transmissions may be more sensitive to fluid level.

 

[MolaKule]

Originally Posted by Pelican
The problem of overfilling is twofold:
1) Additional internal pressure on everything as the fluid expands a lot when hot
2) Foam which does not lubricate and prevents the smooth flow of the fluid



And temperature at filling plays a big part as well.

My 1999 S-10 will shift oddly with an overfill of 3/4 quart but not an underfill of the same amount. My 2012 Frontier will shift oddly with an underfill but not an overfill of about the same amounts.

I usually change ATF fluids during the summer so I can get the trannies as hot as possible so as not to overfill.

Now the more modern vehicles require an ATF temp scan when refilling so as not to overfill or underfill as they seem to be more sensitive to both conditions.

 

[D1dad]

My 09 altima was serviced by the dealer the first time and they overfilled it a tad. I did service number 2 and set it axact and it failed @90k. I can't say whether it was the dealer, me or just a bad cvt in general. Either way, Nissan extended their warranties and stepped up to the plate. I just did my 08 impala tranny and it was underfilled a bit, haven't touched it since and now it reads full after ten miles or so. I know cvt fluid expands like crazy but never seen dex/mercy expand terribly.

 

[D1dad]

The best advice I got on that is to keep the tranny fluid overnight next to the car and do the service cold. I've done that several time per the head Nissan tech and it's really the only way to avoid having the dealer involved. Every time the dipstick is perfect. Put in exactly what you take out.

Originally Posted by MolaKule
Originally Posted by Pelican
The problem of overfilling is twofold:
1) Additional internal pressure on everything as the fluid expands a lot when hot
2) Foam which does not lubricate and prevents the smooth flow of the fluid



And temperature at filling plays a big part as well.

My 1999 S-10 will shift oddly with an overfill of 3/4 quart but not an underfill of the same amount. My 2012 Frontier will shift oddly with an underfill but not an overfill of about the same amounts.

I usually change ATF fluids during the summer so I can get the trannies as hot as possible so as not to overfill.

Now the more modern vehicles require an ATF temp scan when refilling so as not to overfill or underfill as they seem to be more sensitive to both conditions.

 

[mightymousetech]

Originally Posted by Pelican
The problem of overfilling is twofold:
1) Additional internal pressure on everything as the fluid expands a lot when hot
2) Foam which does not lubricate and prevents the smooth flow of the fluid


Additional internal pressure? Huh? It is not a sealed unit, there is still air in there. It will make zero difference in pressure.