Here is a problem that is stumping me! I have '98 1/2 ton with the 5.9. My problem is I cannot get the truck to heat up to the proper temp. First off I replaced the thermostat twice thinking I got a bad one (195) then I replaced the temp sending switch thinking that may be it. The truck takes forever to warm up to what seems to be 170 degrees on the gauge. This provides very little heat in the cab as you can imagine. The thermostat is installed correctly and I even flushed the heater core thinking maybe it was plugged but it had good flow and was clean. With a 195 degree thermostat why does it only heat up to 170 degrees? Also, this last summer the radiator was replaced because of an accident but that still should not affect engine temp when the thermostat is supposed to control that?. It also seems like when you rev the truck a little the heat through the vents gets hotter but the temp gauge really doesn't move. Any ideas? It's cold here in Wisconsin!
thanx

 

That's a tough one. For starters, in the winter time my 2001 2500 will not even get to 210 degrees. It might make it to 195 degrees, but I have the heavy duty engine cooling group and would expect the temperature be close to that of the thermostat.

One thing that I have had happen on previous vehicles is that a bad solder, or connection on the instrument panel, or something bad with the wiring. I would get the engine running warm and stop and disconnect the wire harness going to temperature sending unit and measure the voltage or resistance from the sensor. Cross check that with the service manual to determine what that certain voltage or resistance translates into. That way you can diagnose if it is an electrical problem.

If that's not it, cover your grill with some cardboard as a test and drive around. See if the temperature registers any higher.

Good Luck