My truck has been running hot on the gauge. The needle is going back and forth at a slow pace between the middle and high area and the truck used to never reach the middle section even when towing. I put a autozone thermostat in last saturday also I just changed the thermostat again today with a napa one and put on a new radiator cap. Niether of those have soled the problem. Does anyone have a suggestion?

 

A cummins t-stat installed the right way.
I had the same problem with aftermarket units, threw a cummins one in and problem solved. Also check fan clutch opperation and make sure the core support gound is good and the gauge is reading right.

 

X2!!!

 

I have just put in a new Cummins t-stat and the fan clutch and grounds all seem good. Still having the same problem with my heat gauge. So any advice on how to check that the gauge is working properly or on how to test the tempature sending unit?

 

the going back and forth from middle to hot makes me wanna think maybe you have an air gap in your cooling system. Check to see if your water pump is leaking. My truck had a waterpump that was leaking after it would pressurize. It would get an air gap after a few cycles and would bounce the needle from hot back down then back to hot.

 

On some of the thermostats, there is a small hole in the outer diameter of the large disc of the assembly.

- The thermostat should be installed such that that hole is up at 12:00. It vents the air. That hole may even have a "Wiggle-Wire" in it. It's job is to slightly wiggle in the hole as the coolant flows through. The wiggle action ensures the hole doesn't get plugged.

 

You need a real gauge to tell You what are the temps You are actually running at, if not its just a guessing game. I bought a t-stat form carquest and has worked fine since I installed it, but as stated cummins original equipment is better for some of this items. I also have a radiator in My ford that is at least twice the size of a ctd dodge but I can clearly see the gauge going up to 180f and drop to 140f when the engine is warm.

 

Buy a harbor freight infra red thermometer for $5 and check the radiator outlet temp. I'm found of doing citric acid flush and then a few water rinses. Seems to work better than the autoparts store flush stuff. 100g/gallon.

M

 

A friend of mine lives in southern Colorado, and tells me that you cannot use Tap water. He said that it would clog up the radiator. You might check with the local radiator shops and see if that is the same in your area. Good luck.