Overfilled Transmission

[ejsharp]

Please excuse this transgression. My son just bought a used automatic Nissan truck. When driving it home on the highway the trans would not shift into highest gear. I noticed that the fluid level is very high on the dipstick... a good two inches too high.
Could too much fluid cause the transmission not to shift into high gear?

Many thanks to anyone who may have some knowledge about the situation.

[Ali Al-Chalabi]

Too much fluid can cause problems. It can result in the fluid getting foamed and result in the pump pumping air instead of fluid. I would correct the fluid level then see what happens.

[atikovi]

Or maybe it leaks so much the previous owner filled it high so you can make it home without running it empty?

[C32AMG]

No over fill is not the problem, Nissan have an over drive bottom on the shifter handle, make sure
It’s on. What year and model.

[ejsharp]

It is a 1995 Se V-6 long bed with extended cab. I asked him about the overdrive and he said he was using it. I have not tested the vehicle myself.

Aslo thanks for that bit of info on the bubbles.

[C32AMG]

Nissans have a cold over drive shift strategy, inhibits OD until the water temperature start to
Get warm. If you drive it, get hot and look at the temperature gauge if it does not read operating
Temp. The engine coolant temp switch is bad.

[ejsharp]

As info trickles in... Evidently the no shift into high occurs when trans is hot. Sounds like it may be a foaming problem.

[ejsharp]

Thanks C32,
We must have posted simutaniously. I did not see your info about the temperature guage and sending unit... Wow, Makes a lot of sense. Former owner probably kept adding fluid hoping to make problem go away.

Sending unit might also be disconnected. Any idea where the unit is located?... on engine block or radiator?

You are a gold mine of information. Many many many thanks.

[C32AMG]

Over filling a transmission will cause foaming = Aerated fluid will cause oil pump cavitation,
This causes transmission slippage. Foaming will not cause a transmission to inhibit one shift
And not the others. Now if you pour a box of tide into to the transmission i may agree with you.

[C32AMG]

Thank you, I did not see your last post, Mercedes shop is a gold mine of information, and I am just one worker.

[ejsharp]

C32... Do you know where the sending unit is located? Block or Raditor?

[C32AMG]

It’s on the block by the upper radiator hose. By a new one
And use it to identify the old one.