Just before the thermostat should open, temperature cools or sky rockets and the heater starts to blow cold air. Coolant overflows.
So I shut it down, squeeze the upper rad hose.
Some coolant drains back down. I can then open the overflow cap.
I squeeze the upper rad hose some more and then I can feel heat in the upper rad hose.
Start the truck and alls well.
Other then a shop, any suggestions.