mazdatweaker_2
+1y
You probably need out to bleed the air out of the cooling system.
Turn the heater on full blast and run the truck until the heater core is blowing hot air into the cab. Do this with the cap off.
It sounds like you have a big air bubble in the water jacket, that is unless your head gasket is not working anymore. Why did you decide to put a new thermostat in the truck. Did the truck overheat before this problem showed up?