I flushed my transmission recently, and I overfilled it slightly, maybe by a 1/2 liter on a transmission that takes about 8 liters. When cold, the fluid is a little over the cold mark, but not up to the hot mark.

Will this harm the transmission?

4 Answers 4


Automatic transmissions are very susceptible to damage from overfill. This occurs because auto transmission fluid expands a lot (well, a lot more than engine oil, for instance). The problem it can create is blowing the seals, like where the torque converter rides. The seal itself is not expensive in and of itself, but getting to the seal can cost a lot. It would also affect your output shaft seals. The interior seals/and such may suffer damage as well, but hard parts, bands, and clutches should not suffer any damage.

Needless to say, running around with too much transmission fluid is not a good thing. My suggestion is to get it down to level as soon as possible. As per the 1/2 liter, who knows how much is too much. You may get by with it ... but why chance it.


I agree that overfilling transmission oil is not a good thing but how much overfilling would be more of a concern. I don't think the dipstick can gauge 100% accuracy, it's only a guide range. There has to be some small tolerance for error of over or under filling. I probably would be more concern with slightly under than slightly over filling. How much is to much, not sure but less than 1/2 quart over or slightly just over the full dipstick mark shouldn't be an issue. I wouldn't lose any sleep over it.


I'd say the worst thing that can happen when overfilling an auto transmission is that the fluid in the pan will be whipped into foam by contact with the rotating parts. It will be evident by checking the fluid while running, it'll look like strawberry milkshake from the myriad air bubbles. These bubbles will compress and cause problems when the pressurized fluid tries to actuate the various components, similar to air in the brake lines, leading to slippage, excessive wear and improper shifting.


I'd say neither one of the suggestions above is correct. Having too much transmission fluid in the pan does not necessarily cause the pump inside the transmission to over pressurize the system and blow the seals and I have never seen any moving parts inside the transmission oil pan.

Having the transmission oil pan overfilled with fluid may cause the valve body to become completely submerged in fluid causing the transmission to shift improperly.

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