[Michael C Henry]

The bypass is only supposed to circulate from just under the thermostat to the coolant pump and back through the block again. Coolant is flowing , but just in that circuit. When coolant reaches the opening temp the thermostat, it opensand coolant flows through the radiator .Untill the thermostat opens there should be no flow through the radiator. They do makebad thermostats and they do go bad.If you close off the bypass coolant will be uneven stscking at the top of the cylinder heads. The thermostat will open violently. causing a sudden surge and so forth.