Abstract: An apparatus is disclosed for calculating the steady-state temperatures experienced by an Aluminum-Silicon piston. That piston has incorporated therein an Aluminum-Copper alloy device, such as a band integrally cast within the piston, a setscrew, or an installable wedge that is press-fit into the piston. Preferably, that alloy is a 3.5% to 4.5% Aluminum-Copper alloy that meets the requirements of Aluminum Association Alloy 242 that has been tailored to provide temperature information within 3.degree. C. over the temperature range of from 175.degree. C. to 375.degree. C. The steady-state temperature experienced by a piston in an oil qualifying run is calculated by subjecting the piston to an oil qualifying run of at least one hundred hours, testing the hardness of the apparatus, and calculating the steady-state temperature by reference to a calibration curve.