Abstract: A cooling system for a liquid cooled internal combustion engine having an internal water jacket, a water pump having an outlet connected to an inlet of the water jacket, a thermostat housing including a thermostat and having an inlet connected with an outlet of the water jacket, a heat exchanger connected between an outlet of the thermostat housing and an inlet of the water pump for cooling the liquid in the cooling system, includes a coolant shunt extending from the water pump outlet to the inlet of the thermostat housing whereby when the thermostat is open, coolant flow through the heat exchanger is greater than coolant flow thorough the engine so that heat exchanger cooling is increased and parasitic losses across the water pump are minimized.