I recently purchased a 2018 F150 with the 5.0. Unfortunately, the transmission failed just a week after I bought it. The dealer who sold me the truck had me take it to a shop, where he covered the cost of a used low mileage transmission.

After getting the truck back, I drove it about 600 miles without any issues. However, while driving on the freeway the other day, the transmission temperature spiked to 265°, and the wrench light came on. I also noticed fluid leaking. I let the truck cool down and drove it back to the shop that installed the transmission. They checked it out the following day and found a stored overtemp code, but no active codes or leaks. They did mention seeing some residual fluid from the vent and confirmed the fluid level was fine. The mechanic suspected an air bubble might have gotten caught in the internal thermostat, preventing it from regulating properly.

Everything seemed okay after that, but this morning, I drove in 40° temps, with some steep freeway grades (nothing too aggressive). I cruised at about 75mph for an hour, and my transmission temp reached 222° on the instrument cluster screen. I know these 10r80s run a bit hot, but 220° seems high.

Maybe I'm overthinking it? Could it be a bad filter? Low-quality fluid? Any suggestions or ideas would be greatly appreciated.

 

Ford has a thermostatic valve built into the oil lines feeding the ATF cooler, at least they do on F150's with the 10 speed. That valve doesn't open until 190 degrees. The 10 speed on my truck runs at 206 to 214 degrees all the time. Removing that valve on the F150 will result in a 'transmission under temperature" CEL. Not sure 220 is considered super high temp but worth keeping an eye on it imo.

 

The truck will protect itself from overheating, as it did once already. Unless the light comes back on, you should be fine.

 

an air bubble? sounds like your mechanic is clueless where was the fluid leaking from?? if over filled it will vent out you must have mechanical issue i would confirm fluid level myself my trans rarely gets over 200F with a PPE aluminum pan which probably helps keep the fluid a little cooler used trans probably had issues when it was pulled needs to be completely rebuilt IMO

 

In my experience. the transmission runs coolest when cruising at highway temps (towing and steeps grades being possible exceptions). The reason for this is that the torque converter (a primary source of heat in the transmission) should be locked at highway speeds, minimizing heat. Further, the heat exchanger that is used to cool the transmission is fed coolant immediately off the water pump, which is fed coolant fresh from the cooled side of the radiator (assuming the thermostat is opened). As just a reference, mine runs in the 17x°F range at highway speeds. IMHO, while 220°F at highway speeds isn't a temp that would cause a CEL, it indicates to me something else isn't quite right. By itself, it might just merit monitoring, but with the transmission having actually overheated, I would personally be trying to figure out why.

If you have an ODBII scanner tool, I would recommend monitoring your Cylinder Head Temp (CHT); if your CHTs are elevated (but perhaps not CEL worthy) this will drive coolant temp up, which will drive TFTs up. You might also want to monitor the Torque Converter Slip, especially at highway speeds. If should be at/near zero when the torque converter is locked up.

Another thing to consider is the coolant, and the cooling system in general. IIRC, the '18s would have the older coolant which some have had issues with, causing deposits in the radiator, which was restricting flow.

Lastly, wouldn't hurt to ask the shop that installed the transmission how they checked the fluid level; the transmission needs to be at operating temp before checking the fluid. I don't know enough about the 10R80 to know if it being overfilled could cause heat issues, but just something else to eliminate.