A by-pass valve for a heat exchanger circuit includes a chamber, a fixed surface secured against movement relative to the chamber, a by-pass port including a valve seat located in the chamber, an actuator located in the chamber and that moves relative to the valve seat in response to a temperature of the actuator, a valve member, a spring contacting the surface and the valve seat and producing a force urging the valve member to engage the valve seat and to close the by-pass port, the spring having no structural connection to the actuator, and a return spring secured to the actuator and contacting the valve member for urging the actuator to retract and the valve member to open the by-pass port.