[K204DR]

I've tried almost every thermostat in my truck, and it always ends up the same. Its not in a dodge, but its a 95 dodge motor in my 88 chevy, and I can put in a thermostat, and it will work great for a month or so, maybe two at 180 or so, then all of a sudden it will start running at 150. once in a great while it will go back up to 180 but doesn't stay there very long.
I've tried oe cummins, parts store cummins, and now it has a 77 chrysler 440 one in it. but they all start running 150 after awhile. its a mystery to me. Might try a 24valve one next.