Abstract: The invention is a thermostat for a cooling system comprising a valve member configured to be positioned in a valve port in the cooling system. The valve member is configured to impede or prevent a flow of a thermal conducting medium into or out of the valve port. A thermally responsive actuator is coupled to the valve member to move the valve member into and out of a position that impedes or prohibits the flow of the thermal conducting medium into or out of the valve port. The thermally responsive actuator comprises at least one flexible plate for applying a thermally generated motion to the valve member.