Does anyone outhere know how or what turns on the radiator
fan when it reaches its programmed hi temp limit?
I have a 99 dodge diesel, 24valve, and it overheats if I am
towing or when I go into 4w drive....otherwise it never overheats,
it appears, I am guessing, that there is not enough air flowing
through the radiator, of course, with the loudness of the engine,
I never hear the fan kick into a higher speed..and when it heats, it boils over....above 240 degrees..

Please help...anyone,,,
and thanks...

Ruben

 

I don't know what temp sets the clutch, but many people have reported that the radiator fins are getting clogged from the oil film from the blowby tube. Have you made sure your cooling fins are washed clean? Different situation, but I have a tractor that I was having the same thing happen to. Radiator looked clean, but I had to use degreaser and a pressure washer on the fins. After that, no more problems. Good luck, maybe somebody else will chime in.
Ed

 

He didnt say if the truck was stick or automatic. In several past posts, there appears to be mor problems with the autos doing this when towing and in stop and go due to the auto trans cooler, he might want to check this if auto.

 

Mine did exactly the same thing! After 45 minutes with super clean and a pressure washer on the radiator (after I removed it) and then relocating the breather hose away from the front of the engine the best I get now is just over 190 degrees towing the 5th wheel up a steep grade.

 

Don't know for sure but the TSB's have a bad thermostat doing this on some trucks and only when going up hill or towing heavy loads, Something about cavatation. Look into the radiator cleaning and the tranny cooler etc. I believe the PCM or ECM takes a signal from the ECT and it turns the fan on or up or whatever, Dang computer crap. hope this helps

 

If it has the original thermostat, it is bad, change it. If it is not original I would change it anyway. There is a big difference between the 190 that is speced for the truck and the 180. With a new 190 in mine there is some temperature rise on load, but with the 180 it stays on the center line of the gage regardless of what I am doing.

The fan is viscose and there is no circuitry to turn it on or off. Spin it with the engine off, if it has a drag, it is probably ok. IF it spins free, change it.