Ok. Replaced thermostat with Motorcraft thermostat, pretested on stove, and gasket. Torqued correctly. First time using this click type torque wrench, didn't know it was telling me to stop and I kept going. Broke the bolt off. Got it out though. So theres even new bolts and washers. It is certainly NOT the thermostat at this point. It is back to the fluctuating temperature rather than race to the top. I'm pretty sure the last new thermostat was overtightened. That can cause them to not work right?

I'm thinking clogged radiator now. I took the grill off and was feeling around the fins. Completely cool on the front. Only hot on maybe the top 8 inches on the motor side. And this is while the heater is bouncing between N and past L. I flushed the radiator myself before I took it to Jiffy Lube and had a coolant flush there when this problem first popped up last week.

There is no noise from the water pump and its not leaking. The fan is working as it should. I have no leaks. When filling the coolant I had the truck running with the heater on. I don't have any heater core gurgling. I'm pretty confident its not air in the system.

New radiator time.

 

dont mean to insult you but ive seen guys put the thermostat in backwards. just checking