My reason for installing a valve was to prevent a bypass situation of coolant through main radiator, as a Kitfox IV floatplane I was concerned with water temp on climb out in the heat of summer, and the plumbing of heater core allows for coolant heading to rad to bypass through heat core back to water pump inlet, so I installed a rugged ball valve made from plastic on outlet side of core under dash, within reach to block flow in summer, can regulate in winter on skiis..Been working great,