In my 2002 Dodge 2500 Cummins Diesel my water temperature gauge fluctuates to both ends of the gauge (from 140-240). When it first happened I stopped and popped the hood and could tell the truck wasn't at 240 like the gauge said. I limped home and let it sit all night. Went outside in the morning and turned the key on and the gauge immediately rose to read the temperature at 240. This showed me it was truly not overheating. In order to try to fix it, I have replaced the water temp. sending unit and the thermostat. When neither of these helped I installed a mechanical temp. gauge which reinforced that the truck was in fact not overheating (or dropping to 140) as the stock gauge would occasionally say.

Any ideas on what is wrong and how to fix it?

 

Bad ground at the gauge? Wiring problem?

 

Did you recently do any type of work to it that required you to drain the coolant? If so, it could be an air pocket in there that's causing the problem.

 

Where is the ground at the gauge located?

Recently I replaced the water pump dropping most of the coolant. How can I get the possible air pockets out?

 

Download the factory service manual from the FAQ section here. It is for an 01.... but, I think the 3/4 and 1 ton trucks didn't change until 03?? (Don't quote me on that, I am unsure.)

 

https://dodgeforum.com/forum/2nd-gen...-bleeding.html
https://dodgeforum.com/forum/2nd-gen...-bleeding.html

 

ive put 3 coolant temp sensors into my 360 over the years, for some reason they like to go bad. for my motor they were like 12 bucks, cheapest place to start i would think.

 

Cheapest place to start is to make sure the cooling system was properly bled after the water pump installation. It only cost you time.

 

How high should a guy raise the front end of the truck to bleed the cooling system? Thanks for the links above but they weren't real specific on how high the front end needs to be lifted.