Transmission temp top hot?

[Bramic71]

What year of 2500. I am pretty sure my 2021 doesn't have the thermostat in the line or at least it usually runs at 160 to 170 no matter how hot it is outside.

Ours is a '22. Ours did have the thermostat block in-line.

 

[caulk04]

As far as any confusion on whether or not 2500's have a thermostat or not, they do. There have been thermostats in trans cooler lines for decades. They started out as a simple bypass that would send the fluid right back to the trans without crossing the cooler until it reached the thermostat temp. If you're seeing a consistent trans temp regardless of ambient temp, there's a thermostat. If one of those thermostats happened to fail, the trans would still run hot but it wouldn't be FORCED hot by 200º+ coolant temp on top of the internally generated trans temp.

It's much more recent that vehicles have been including HEATER circuits with engine coolant like the 8HP in our 1500 Rams. My wifes 19 Fusion and daughters 15 Jetta both have heater circuits utilizing engine coolant.