Abstract: A thermally actuated valve employs a plunger and bore valve configuration. A thermally expansible wax actuator has an axial length that changes in response to the temperature in a cavity of the valve. The plunger integrally extends from the actuator body and carries a seal. At temperatures above a predetermined set point, the actuator produces axial force sufficient to extend the length of the actuator against a return bias and project the plunger and seal into the bore, closing the valve. At temperatures below a second set point, the axial force of the actuator is less than the return bias and the plunger is withdrawn from the bore, opening the valve. The axial force generated by the actuator is variable and has a non-linear rate of change, providing a valve with a non-linear change flow rate with respect to temperature.