Coolant Temperature Sensor
Heater Control Valve
It will run a little warm and then get off the highway and bam! Shoots straight up. I've pressure tested the system to 17 lbs. The tube on the top of the water pump started leaking at 18 and I resealed that up with some metric O-rings.
I know it could be the dreaded Head Gasket but there has never been any oil on the dipstick or under the fill cap.
Today I'm going to check if my new thermostat is stuck open, reseal that inlet tube and see what happens.
If it turns out to be the head gasket I need some help on how to make it happen with a daily driver. I figured I would buy an old head off someone and have the machine shop here in town work it over. Then I could just take a few days off and stick a new head on it.