Abstract: A liquid cooling system for an internal combustion engine includes a coolant pump, an air-to-liquid heat exchanger, and a bypass loop for allowing coolant to circulate from the coolant pump to the engine without passing through the heat exchanger. A thermostatic valve mounted within a thermostat housing and including a temperature-responsive primary valve element and bypass flow control will control the flow of coolant with a spring-loaded valve disc having a conical, annular sealing surface configured for linear contact with the valve seat.