So changed out thermostat, fan clutch and radiator. I drive on the freeway for 20min and the gauge starts to go up half way. Once I get off freeway truck starts to cool down. Do I need a bigger radiator, just recently starting to have this problem. driving around town is fine, Not loosing coolent and no leaks any where.

 

Check that your ignition timing is correct and that the timing advances with speed and load appropriately..

 

Did you burp the system?

 

 

Yeah, air bubble or bad thermostat would be my first guesses.

 

 

Yes, but is the new one working correctly. It can be tested by pulling it out (yeah, I know it's a pain) and placing it in a pan of water on the stove. Using a cooking thermometer, slowly heat the water and see what temp the thermostat opens.

 

I don’t see the radiator fluid circulating. So thinking of changing the water pump out.