A thermal imaging system has been developed for viewing and recording the cylinder head surface temperatures of an internal combustion engine. The system consists of an I.R scanner, associated calibration and image processing equipment and an infra-red transmitting window mounted in the piston. The infrared window material used (silicon) has thermal characteristics close to those of a normal piston. The two dimensional temperature distribution of a cylinder head surface has been measured during start-up. The imaging results from the camera were checked against the readings from the thermocouples fitted into the cylinder head. The agreement was very good, and gives confidence in the system.