[II Sevv]

Just picked up my first ever diesel up in Salt Lake City, and drove it back here to Phoenix. The entire way home, even in the 30 degree ambient temps in Utah, I saw trans and coolant temps above 200, with the coolant staying constant between 204-208 and the trans around 208-10, but going as high as 217-218 when in highway sections that required the trans to shift. I’ve read the radiator fan doesn’t come on until 217 so I’m okay with the coolant temps, but that trans temp seems extremely high for being unloaded, on the highway, in the cold. I got it home, changed all fluids including dropping the trans pan and changing the filters, and pressure washed the trans cooler/AC condenser as I’d heard that helped some people. Quite a lot of dirt came out, but it didn’t help one bit. I drove the truck around in my neighborhood and saw trans temps as high as 226. My ford raptor with 37’s never even saw those temperatures while rock crawling in the summer heat. This is in 50-60 degree winter temperatures. Does anyone have any insight as to What is going on? Bad sensor? Or is the cooler just completely screwed up? It also seems like there are two coolers, one up front and one on the side of the block, do I replace both? I’m scared to even drive the truck around town until I get this fixed so any help is appreciated.

 

[BRK44]

ECT is a non issue. The stock thermostat should open at 200 and correct, the fan clutch will engage at 217.

Those are higher than normal temperatures on the trans. In the ND summers I pull my 10k TT all over the place and haven't seen my trans temp above 180. Even when I needed a new thermostat and fan clutch, which caused my ECT to reach nearly 230, the transmission stayed normal at 175(ish). I can't solve your problem, but can confirm that it is a problem.

I'll beat the usual questions and ask for more specifics so others can help more. Miles, modifications, tuned or stock, tire size, etc?

 

[II Sevv]

ECT is a non issue. The stock thermostat should open at 200 and correct, the fan clutch will engage at 217.

Those are higher than normal temperatures on the trans. In the ND summers I pull my 10k TT all over the place and haven't seen my trans temp above 180. Even when I needed a new thermostat and fan clutch, which caused my ECT to reach nearly 230, the transmission stayed normal at 175(ish). I can't solve your problem, but can confirm that it is a problem.

I'll beat the usual questions and ask for more specifics so others can help more. Miles, modifications, tuned or stock, tire size, etc?

Yeah, I reached the same conclusion. It has 220k, it is tuned but even when I set the minimaxx to stock power levels it still gets real hot. It’s on 35’s but again I was seeing these trans temps just driving around town and cruising on the highway in the cold almost 220 degrees. Other than that it isn’t modified and the trans shifts great. I talked to a transmission shop this morning and he suspected that since my year truck doesn’t have the thermostat on the side of the trans that it’s probably an issue with the stock cooler. I have an aftermarket one sitting around so I’ll probably throw that on.

 

[Pneuman]

Clean the radiator and trans cooler, these will collect dirt and dust, reducing coolong efficiency. Check trans fluid level and change coolant, also effects cooling efficiency.

 

[#40Fan]

2010-2012 68RFE Transmission Cooler Thermostatic Bypass Upgrade - Revmax Converters

 

[Duelly Dad]

Doesn’t sound right to me, doesn’t the 12 have a 190 stat ? If it has a 200 stat you would see numbers from about 205 to 208. The trans temp are high, mite need the bypass upgrade.

 

[5.7 Hemi]

Funny, my 11’ doesn’t have those. The summer of 21’, coming back from Lake Nacimento, I saw trans temp hit 225 in the hills. That was enough for me to get a Derale auxiliary trans cooler with fan. I mounted it under the bed just behind the fuel tank, ran 32ft of -8AN lines. Highest I’ve seen the trans hit now is 170, that was pulling our enclosed trailer full of household stuff (moved out of Commiefornia to Texas) going up the hills (9k loaded trailer) without the fan on. And yes, stock temp for the thermostat is 200.

 

[II Sevv]

2010-2012 68RFE Transmission Cooler Thermostatic Bypass Upgrade - Revmax Converters

That might be exactly what I need. After talking to 2 transmission shops and them telling me I don’t have a trans thermostat due to the truck being a 2012 and that the thermostat was in the cooler instead, I bought a new (and bigger) trans cooler. I ripped the stock one out and cut it apart from the condenser in order to mount the new one so it’s too late to go back so I’ll hope maybe the cooler was just clogged like the shops said. While going through the engine bay to run the new lines I found I did have the block installed next to the fuel filter so it’s seeming like the shop might have been wrong.