I can run all day... stop and go.. interstate... steep inclines... and the temp gauge stays steady at just a hair below dead center but then if I shut the truck down for 10 minutes or so and start back up it has trouble getting the temp back where it was and begins fluctuating between 1/2 and 3/4 on the gauge. Any ideas why after the shutdown the temp is having troubles?

 

thermostat could be sticking open...also is it belt fan or electric?

 

Belt fan