Many studies of heat loss reduction by insulating the combustion chamber walls have been carried out to improve thermal efficiency in internal combustion engines, but most of them have not been successful because of intake air heating as a result of high wall temperature even in the intake strokes, which deteriorates charging efficiency and exhaust emissions. Toyota has developed a new concept by a thin heat insulation coat with low thermal conductivity and low heat capacity. Toyota Land Cruiser Prado achieves a heat loss reduction by decreasing the temperature difference between the in-cylinder gas and wall temperature by quickly changing the wall temperature in accordance with the transient gas temperature. This technology was applied to the pistons of a passenger car diesel engine, thereby helping to increase fuel efficiency and exhaust gas temperature, which is effective for fast warming up of the exhaust after-treatment system. As the results of heat balance analysis, heat loss is reduced, leading to higher brake work and exhaust energy.