My truck over heated in idle yesterday . Once I start driving its fine . I noticed this happened about 1 year ago but I never adressed it . It seems to be getting worse now . I dont idle often for long so I kinda forgot about it .

Could be unrelated but the AC dosnt blow cold during idle also . The serp belt seems snug .

Is this most likly a water pump going out? Any tips on trouble shooting the problem?

 

Flush the radiator w/new antifreeze (2gal), clean the radiator fins, replace thermostat w/factory cummins part. If the wp is going out it will begin to drip from the bottom of the pump like all the others.

 

most likely you fan clutch is bad and not pulling air when stopped when your driving you have ram air affect

 

I would make sure the radiator fins are clean. Unless you changed it, yours has a little puke bottle on the lower driver side of the radiator. They are notorious for misting oil fumes on the back of the radiator causing it to pick up dirt. One of my friends complained about his overheating and when we looked the back side was literally 70% caked with dirt.

 

I second the puke bottle /radiator fins clogged with junk.

 

Agree with cleaning the fins.
You can back flush the radiator with a simple home made tool that attaches to a garden hose. Copper pipe sealed off on end and small holes drilled on one side to give water pressurize. Slides down backside of radiator nicely .
If using bottle for crankcase pressure release.... pull your radiator and clean it good. Still want to flush fins from backside!

Most replace botle with 3/4" hose run straight down and attached to axle with zip tie.


RJ

 

I made the same type of homemade tool but I use compressed air. If cleaning does not solve the problem I would change the water pump, the fins could be worn enough to not circulate the antifreeze. The radiators are so huge that they cool really well while driving.