Abstract: A two-stage piston in a thermostat's thermal actuator is configured for degassing entrained air from a coolant system. The first-stage part has a cylindrical shape and is terminated at one end with a rounded-conical shape and having a cylindrical cavity at an opposite end. A second-stage part has a cylindrical shape with a diameter sufficient to fit within the cylindrical cavity. A sacrificial plug is formed of a wax-like substance with a melting temperature such that the entrained air escapes from the coolant system through the thermostat. The diameter of the sacrificial plug allows placement of the sacrificial plug in a bottom of the cylindrical cavity and a length of the two-stage piston with the sacrificial plug in place forces the valve to remain open. After the sacrificial plug has melted, the length of the two-stage piston will open and close the valve with a change in coolant temperature.