Neighbor has 02 2500 with AT. The Temp gauge will go from nothing to pegged and then go back down to nothing. Thermostat is new. Thinking sending unit is bad. We unhooked the temp sender and it pegged the gauge.

Any thoughts would be wonderful.

MM

 

Did you get all the air bled out of the cooling syst. after refilling it? It could be an airlock.

 

Not uncommon for senders to give up after a while on these. I have replaced both temp and oil pressure on mine.

A pegged gauge is usually a sign of a bad sender unless you are experiencing other signs of overheating...blown radiator cap, steaming, strong odor etc....

Right now in AK I would be surprised if you could get the temps over 200 towing a trailer uphill with the e-brake on!!

 

New engine coolant temperature sensors at around $10 each from Cummins and Geno's garage.
Just put a new one in my truck while trouble shooting other problems (VP44 replaced).