Basic question is do I have a bad sensor or something else? dash gauge reads 3/4 to the red at long lights. Takes a little while to get there. Last week in 107 weather in rush hour stop and go traffic for 80 miles I had to run the heat. I changed the fan clutch just before that trip. next day I changed the radiator and thermostat. Tested both the new and old one together and old one was only opening half way if that. runs cooler but still not like it should. I have a laser thermometer and the neck of the hose (metal) just above the stat reads 194-211 on a pretty constant use. 211 gets me 3/4 to the red on the dash gauge. 40 degree drop from that point to the lower hose connection of radiator. The clutch never gets warm enough to fully engage and cool down things more. 225,000 miles on the 5.9 gas and I replaced old heater core last winter and water pump a few years ago. Upper hose is new. Only thing left is bottom hose, pump or head? No loss of fluids no gain of fluids (oil).

 

What temp does it run on the highway? If it runs the correct temp on the highway, but hot in traffic, the fan clutch has probably gone south. With the motor off but fully warmed-up, can you turn the fan?

 

yes even at highway speeds it runs hot. Yes warmed up and the engine off I can turn the fan on the new clutch just as the old one but one note on that even the others I replaced over the years I could do that with them warmed up. The only difference I've ever noticed on the new fans is that I can hear them engage sooner. reving the motor by hand (throttle body not the foot) with the new radiator the new fan never engages like it did before with the old one.

 

one thing you can do is get a thermostat that opens at 180 degrees rather than the stock 206 ..

http://www.highhorseperformance.com/...1L_p/10183.htm

 

You may have multiple problems. It should be nearly impossible to turn the fan if it's hot - you'd be nearly trying to turn the whole motor. If it's hot on the highway, that sounds like clogged radiator or stuck 'stat.

 

I think a coolant flush might be needed. I'd also be looking at a 180* t-stat for that old 5.9. Running your engine that hot hurts the transmission too. You should look at your cat too, if it's stopped up it can cause your engine to run hot. Look at your fan clutch too, not entirely impossible that it hasn't gone out.

 

thanks for the help. Turns out the first thing I replaced, the fan clutch, was bad. The old one worked better than the new one in the end. Got it replaced under warranty and everything works great now.