The heat insulated four stroke light duty d.i. diesel engine for cars was developed at Elko in the last 15 years. The main development aim was to find practical solutions to increase fuel efficiency. Heat insulation means reducing the flow of heat from the combustion air to the engine components.For this purpose a new combustion system, that is to say an air/fuel mixing process, was developed and new engine components were built and tested and the engines cooling system was adapted to the reduced requirements. For automobile applications it was further postulated that the new generation of engines would have to improve upon i.d.i. diesel engines on following points: a) Torque and Power or rather acceleration, and maximum car speed per swept volume, b) Combustion noise, c) Cold start.The development results, that is to say heat insulated light duty d.i. engines, have so far been tested in about 15 cars and a total of well over 1 million km. Test results show a mileage improvement of on average about 30% as compared with i.d.i. diesel engines and a reduction in fuel consumption of 40 to 50% as compared to gasoline engines. The postulated improvements concerning torque, power, combustion noise and cold start were all achieved.