I have some heat issues with my 01. A few weeks ago I did a complete coolant service on the truck I pulled the radiator, flushed it and degreased exterior. Flushed the block and heater core with water until everything ran clear. Installed all new hoses, new Cummins thermostat, new thermostat housing and filled with 50/50 mix with Preston Low Tox and distilled water. Have run the truck for about 500 miles and have some issues. The truck takes 20 to 25 minutes to truly warm up. I can watch the temp gauge get to operating temp 190 and then drop down to 175. This goes on for 5 or 6 cycles. Confirmed these readings with OBD scanner and live data through truck port. Once it gets to running temp the truck runs between 185-190. The heat blows warm not hot. On first and second position (low speed) of the fan the heat is warm. Third and and forth position (high speed) the air blows cold. I am not losing any antifreeze and do not smell anti freeze in the truck. Checked passenger side floor for leaks and it is dry. I am thinking the heat issues is a heater core but before I go through the aggravation of ripping the entire truck apart to do this I wanted to see if anyone had any other options. Also any reason why the fluctuation in temperature on the truck. Also I changed the oil after the coolant flush and it was pure oil. No water in the oil.

 

could be your thermostat sticking open i know its new but you could of got a bad one

 

i agree, its possible you got a bad 1

 

I don't think it is sticking open as it when it finally "warms up" it stays closed.

 

the only other thing i can think of is maybe a bad heater control switch??? Ive heard of a few fords and jeeps having that issue so maybe???

 

Any way to test the switch. You have to buy all the switches and its like 160 bucks from the stealership

 

i think if you get one of the haynes manuals they tell you to use a mutimeter and test the continuity and the volts readings. Mines at my shop, ill look it up and get back to you tommorrow.

 

They had a bad batch of t-stats. As long as the heater blows warm or hot, and not cold one second and hot the next, you at least don't have a head gasket issue.

 

Try replacing the radiator cap. i had the same issue with fluctuating temps. new radiator cap and thermostat fixed it.

 

thats a good point def. try the radiator cap, never even thought of that