02 Eng cooling sys questions

[Tail_Gunner]

And yes I did replace the thermostat. The stat came from NAPA and has the Navistar part number stamped in it, so I'm sure it's correct and seems to be working properly.

Be aware of a possible issue here. IIRC the correct T-stat will be a Ford unit. Even though the engine was built by Navistar, I've heard it said several times the water pump was not, it is a Ford waterpump. If that is true, then a Navistar t-stat may not be right. I think I heard there was some difference in height between the two.

 

[Hooper]

Well, my radiator swap did the trick. I did another test run on the same route, though alittle cooler ambient temp but with very positive results.
The fan clutch came in as it should and the coolant temp never got above 215, PROBLEM SOLVED!!! Yea Ha!!
I obviously didn't do a good job of diagnosing the radiator in all of this. It is interesting that there was enough restriction in the radiator to cause the f/c to not "see" enough temp to cause the f/c to come in when it should have.
Thanks for everyone's thoughts and help.