In Reply to: thermostat question posted by Curby Perkins on November 30, 2018 at 00:48:28:
Had that happen to me on my TO-20 once with the same type thermostat in the top radiator hose. Problem is the thermostat is trapping air between the thermostat and head and not opening. I ordered another thermostat from another supplier and problem solved. Doing additional research afterward I discovered the thermostat needs to have a small hole drilled in it to allow trapped air to vent to the radiator.