Ok since i had the truck temp Gauge moves up to the C never no more.. So i took the thermostat housing off .. I belive the T -stat is in backwards or on cummins it sits with spring to the hose.. I was always told spring side towards motor.

 

there should be a little arrow on the thermosdat that says " to radiator" or something like that. i put mine in backwards before and had the same issue. i cant remember what side goes where though.

 

I am 99.9% sure spring side goes towards the motor. I went and changed it letting her run now we will see

 

hmm. i hope it works.

 

it only goes in 1 way, otherwise it just barely hits the housing.

 

Not really it will both ways and if im right will work both ways just not good one way

 

What brand thermostat? Most aftermarket ones dont work in our trucks. You need to cough up the money for a Cummins brand....

Also make sure the hole is up.