Abstract: An automatic heat exchanger tempering valve designed to maintain a consistent temperature of a fluid within a machine. The tempering valve is configured to sense fluid temperature and in response, to proportion the flow of the fluid from the machine between a heat exchanger and an either internal or external by-pass flow circuit. The valve includes a movable valve diverter positionable in multiple positions to create a variety of proportionate flows of the total fluid flow stream between the heat exchanger and the by-pass flow circuit. The valve diverter is positioned by a multiple position valve actuator that changes the position of the diverter by reacting to a change in fluid temperature. The valve and the bypass flow circuit are easily installed within a motor vehicle by simply splicing into the two radiator hoses in the engine compartment.