my 01 cummins has been having some issues getting up to normal temps now that the weather is cooled down, i regularly drive 40 to 50 miles a day and the highest my temp gets is 150 and as soon as i stop at goes straight back down to 140, even on days when its not very cold outside itll heat up a little bit more then 150 but thats it so i dont think it would be the thermostat, i really need some help so i have a heater before it gets real cold out here thanks

 

That sounds like a thermostat that is stuck partially open to me. They're supposed to be developed so that they fail in the open position so that you don't have overheating issues.

 

I almost bet money its a thermostat mine was doing the exact same thing stuck in the open position and my truck wouldnt ever get up to temp. I just replaced it 2 days ago. $26.99 at my local autozone.

 

Get ready to replace it again....... get one from Cummins.

 

I know the bigger cummins have an inner seal in the thermostat housing that seals on the outter circumfrence of the thermostst, if that is bad it won't build heat. However I'm not positive the "B" has this.

 

Are they really that junky???

 

Sometimes they are. I've had an autozone t-stat for 3 years, no problems yet. (now that I said that...)

 

there is a huge difference between an OEM stat and aftermarket, some like stant (excellent thermostats by the way) dont work well in a cummins, I ran a stant and chased heater issues, the gauge would read 190, but not alot of heat in the cab, I changed every part except the thermostat, as you can see by the pic, the oem has a plate to re-direct coolant thru the heater core, the stant does not