Isuzu NPR cooling system help

Thomas C

New member
My work truck has cooling issues. Does anyone here have experience with Isuzu NPR trucks. On the open road it runs cool,but in town it wants to get hot, the gage pegs hot.
I just replaced the thermostat today and that does not seem to be the problem.
It is a 91 Isuzu NPR Diesel turbo. It has sensors above and below the thermostat. I have worked on gas engines but this is my first diesel motor.
Any help would be appreciated. Thank you.
 
I am thinking your fan is not working, The airflow keeps your truck cool going down the road with no stops, but the city is stop, go, stop, go with low speeds and your over heating..... Check your fan, it could be a fan relay also!
 
I am thinking your fan is not working, The airflow keeps your truck cool going down the road with no stops, but the city is stop, go, stop, go with low speeds and your over heating..... Check your fan, it could be a fan relay also!

Thanks Jeff:cool: I am a little out of my element with diesel motors,turbos etc...
 
Call me if you need anymore help I worked for Cummins for quite awhile! I'm on a computer in the public library right now. Don't have mine with me.
 
Call me if you need anymore help I worked for Cummins for quite awhile! I'm on a computer in the public library right now. Don't have mine with me.

I just might take you up on that Jeff, Thanks man



i dont think the izusu's have electric fans,at least mine doesn't. try washing out the cooling fins in the radiator might just work. also check the blades on the fan sometimes they get bent or out of shape and dont pull air.

Thanks Greg I'm going to try that to. It has a declutching type fan. It seems stiff when you move it by hand. Thanks for the help.
 
Fan clutch may be bad, if thermastat is working and all fluid levels are correct. Clutch runs fan at low and idle speeds. Run engine with cab up and see if it's (fan blades) spinning with the same speed as the belts.
 
Get the service books, it'll help a lot with all these and other probs.

I bought mine for the 94 NPR I have.
 
I agree with Tim, if you fan clutch is bad it will not cool the engine.

My truck had an electric fan clutch and the wire got cut then it would get very hot just driving around town or at idle but on the highway everything is fine.

If you have a fan clutch it is hard to tell if it is bad. Grab the fan blade and give it a hard twist and usually it will not turn a complete rotation, if it does it is bad but it could be bad even if it does not turn all the way thus how it is hard to tell.

Once I had the electric fan clutch changed out everything went back to normal.
 
It came down to replacing the radiator. I replaced the thermostat,flushed the radiator and that did not do it. Radiator was the problem...All better now:cool:
 
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