Automatic transmission 4x4

Transmission rebuilt at 90,000 miles due to water from radiator cooler leaking into transmission. Mechanic said transmission water cooler was not needed in Puerto Rico since temps never get below 65 so it was disconnected. Is this smart? Advanced Auto fluid was used not Nissan. Transmission slips after 10 miles of use. I put it in 4 wheel drive for 200 yards…it leaked fluid and would not go forward or reverse until it cooled down. Mechanic said it was due to water vapor still in transmission. He said he would take the dipstick out, I should drive it 500 miles that should get the water out and everything would be fine. Job cost me $1285.00 w/6 month 6000 mile warranty. I haven’t gone 50 miles and don’t have much faith in “just drive it and everything will be fine”. Could someone please advise on this matter. Thanks.

What they disconnected from the radiator is the transmission fluid COOLER. Without this connected the transmission fluid has no source of getting rid of it’s heat, so the transmission overheats and the transmission is destroyed.


What this mechanic said was that the transmission ccoler to the radiator heated the fluid in the transmission to work properly in cold climates and is not necessary in a warm climate. He also said, if it’s not connected you will have no water problems, since there’s no water. Please advise

This is completely backwards. The transmission gets hot and the manner used to keep the transmission cooler is to cool the transmission fluid. In your truck the transmission cooler is integrated into the radiator.

If you wish you can buy a separate transmission cooler and mount it somewhere so it can get enough airflow to cool the transmission fluid. This way you’d avoid the possible mixing of transmission fluid and coolant when, or if, your radiator should fail.

I can’t believe your mechanic has the story so backwards. This sounds like a miscommunication. If the mechanic believes the story as you wrote it in your post then you need a new mechanic - pronto.

In Puerto Rico you need to cool your transmission to prevent heat damage. This is a warm climate. If you operate your truck in hilly areas, drive it on the beach, pull any kind of trailer, or haul any loads your transmission needs a cooler.

They have it backwards.

It’s the transmission fluid cooler in the radiator. Not the transmission fluid heater.


You’ll destroy the transmission (overheating) before you get anywhere near 500 miles.

Find another mechanic. The one who disconnected the transmission cooler doesn’t know what he’s doing.

One thing that I can not seem to find any info on is this water vapor in the transmission…any ideas what that is all about? I appreciate all the replies. Thanks

I doubt this guy has the skill to rebuild a transmission in the first place…I mean, didn’t he just tell you he rebuilt the transmission but somehow did not get all the water out?? So he must use the “Wet Rebuild” method…Good Luck…

Now, lets talk about the torque converter. Was THAT replaced??

You have been taken, the transmission fluid is circulated through the radiator to cool the transmission. If the transmission fluid cooler leaks it allows transmission fluid into the radiator and water and antifreeze into the transmission which destroys the transmission. There is no water vapor involved. Your "mechanic’ is either dishonest or completely incompetent

I believe that my truck has two coolers…is that correct? Perhaps a smart thing to do is get a manual. I feel that I need to have this fella make good on the money I just paid him and in order to do so, I need to have more knowledge on how all this should go back together. Thanks for your help.

Hi Uncleturbo,
Just started poking around the internet at the Nissan Forums and happened to see at the Consumer Affairs website a handful of people with 2005 Frontiers having the same problem as I am. They determined that the radiator was faulty and leaked fluid into the transmission. These folks went to Nissan dealerships and also wrote to Nissan Affairs, but received no help. They were going to be out of pocket anywhere from $6,000-$8,000.00 depending on their location. So…with this in mind about the radiator perhaps the way to go is with something that will cool the transmission without involving the radiator. Would like to know if you’ve heard anything about this issue with the radiators being faulty. And can you suggest some alternative if the radiators are an issue. Again, thanks for your time.

Personally I don’t own a Nissan and haven’t researched your problem, but I do believe there is a problem with the radiator set up.

In your truck one radiator has two separate sets of pipes and tubes going through it. This saves space but if something goes wrong it can allow the two separate fluids (which are very different in composition) to mix together. If there is a breach you can get transmission fluid in the coolant, not good for the motor; or antifreeze coolant in the transmission, not good for the transmission.

What I suggest is going to an auto parts store where you can buy a separate transmission cooler. The lines running into the current radiator can be capped off and the transmission fluid can be routed through this separate transmission cooler. This will keep the two fluids separate in the future. Perhaps a radiator shop can make your current radiator solid enough to handle the normal motor coolant and you won’t need a new radiator.

Frankly, I don’t have much faith in your current mechanic. I’d look for a good transmission specialty shop to install the trans cooler and to evaluate the condition of your transmission.