01 Cummins not heating!!!
 

So after towing a trailer for a buddy, my truck will NOT warm up. Even driving for 15 minutes at highway speed it wont get above 145*. It will fluctuate between 118* and warm up to 140ish* and then fall back down again. The heater grid even cycles too. I had to put a piece of cardboard over the radiator all the way across to get up to 170* at highway speeds, even then cooled down to 150's when going 50mph. Anyone know how i can fix this? The temp outside is only 36*and I can't for the life of me figure out what could be wrong. Thermostat stuck open maybe? Thanks guys!

you said it. thermostat open i think

thermostat could be stuck open like you say i would check that first:humm:

X2 Check the thermostat I would just replace it, its just good PM while you have it apart. And also is the coolant level full and ok wouldnt hurt to just flush the radiator while you are at it.

I agree with blkjack change thermostat and flush at same time

I would do the thermostat too. I prefer the ones from Cummins over the parts store stuff.

Updates??