In this study, a measurement system is developed for obtaining continuous piston temperatures in a working engine by using a voltage recorder. The developed system has a very high accuracy with a measurement error within ± 1 °C. Since there is no relative movement between the measurement system and the piston, its reliability significantly increases. In order to test its accuracy and reliability, the developed measurement system is used to obtain the piston temperatures under various operating conditions with different air-fuel ratios, oil temperatures, and engine speeds. The measurement results are then used to calibrate the piston temperature field simulated by numerical analysis.