Why is my transmission fluid overheating?

Hello i have 2008 Tundra limited 4x4 5.7L I have been getting this problem since long time when i drive in highway and:
1- when i go faster thant 70 miles/hour for 30 min or more
2- when i drive 60 mlies/ hour and slow down for traffic or take and exit

I bouth this truck with this same problem and after a year the reverse shit stop working cause of this continuos overheatings . So I took it to a workshop and they rebuilt the transmission. I didnt use to much the truck the first moth and when i start going for the highway i relace that the problem that cause the overheating still persisten.

They just rebuilt the transmission, the harness , torque converter, valve body and solenoids are the same.

I already have flush the transmission cooler and houses. And have no idea what is causing this issue.

i have been checking fluid temperature with a scaner and normally is between 170 - 220 f ( I dont know if this range is normal but the the transmission fluid gauge stay in the middle) when it start getting over hot it goes until 350-500 f.

I will be very thankfull if somebody could give me a hand.

 

Does it have enough oil? Have you tried pinning the thermostat open to see if that makes any difference?

 

Yes fuild level is correct. I have not drive leaving the thermostat manually open with a pin. Do i should try it ?

 

I would

 

I am going to try it tomorrow in my way to work. Another thing that has me intrigued is that I feel a noise in the transmission with the ignition on , engine off and transmission off i can feel a noise and vibration inside the trasmission . I have test all solenoids and when i turn of the solenoid SL2 the noise and vibration stop . Its that normal ?

 

If you've run the fluid up over 300°-500° I'd suggest changing it as well. That stuff is cooked.

 

I tried drive with pinning the thermostat open and it improve a lot . Now when i slow down in the highway oil temperature goes until 275 f . At fuild gauge goes around 70 % and starts to decrease until 200-180 f.
Now what part do i should replace ? I have been looking for At cooler temperature control valve or transmission thermostat and nothing pull out from Amazon or ebay .

Thank you AZBoatHauler for your advice and the others opinions.

 

Sounds like the thermostat might be bad. What trans temp are you watching, torque converter or pan temp?

 

In my scaner appears variables AT transmssion oil temp 1 and AT transmssion oil temp 2. I was checking both but temp 2 was really mathcing with trans temp gauge in the instrument cluster.

What is the real part name of the thermostat ?, i can not find to buy it online

 

https://parts.lakelandtoyota.com/p/...-Automatic-Thermostat/4044829/3297034030.html

 

Before investing in a part, assuming you have the tow package and you have a transmission cooler, even if you don't. I would trace them cooling lines to the transmission cooler or the radiator. Check to see if those lines have been crossed, meaning your transmission is ingesting the hot fluid vs cooled fluid. That may be your issue. My assumption is, if your thermostat was bad then you would be heating up within the first 15 to 30 minutes of driving anywhere since your transmission is getting warmed up. Additionally, both sensors are reading pretty similar and assuming accurate temperature readings. Since your transmission was rebuilt, I would go back and check your cooling lines to ensure they're correctly routed to the appropriate place. If you look on youtube you will find some videos showing which ones go where. All the information will not be in 1 video so you may need to source a few of them to get all the information you need.

 

Crossed lines would only result in the fluid flowing through the cooler in the reverse direction. I do not believe that this would cause any problems or change in performance of the cooler.
I would be temped to verify that my temp sensors are correct. At 350 plus degrees for any period of time, I would expect that the fluid is beyond toast and that the transmission would be exhibiting some other significant problems. If the truck drives well, I would verify the fluid temps first.

 

Agreed. The difference would be minimal from swapped lines. Plugged or pinched lines come to mind. When I pinned the trans stat open for fluid change, you could feel the difference in the in the out bound temp vs return temp even sitting in the driveway. An IR temp sensor also confirmed what I could feel.

Things that escalate trans temps.
Clutches and bands slipping from low pressure.
Torque Converter never in lockup.
Plugged feed ports. The fact that pinning it open shows it has some flow but you have to wonder if it's enough flow?

How was the solenoid identified? Techstream? Iirc Techstream can exercise some tests.

If this were mine I'd verify flow through the heat exchanger, thermostat, and cool + lines.

gl

 

If that temperature is real, then chasing cooling is fruitless.
Without cooling the trans should not get that hot unless there is a problem with the transmission.
You should go back to the guys who rebuilt the transmission and they should make it right.
Or..... You have a bad temperature sensor.

Your fluid should look and smell like death at this point. How does it look?