Calculating heat balance of Otto engines, one can recognize that the ratio between heat transfer and power increases in the part load range, i.e. city driving. To improve the efficiency of such engines it is necessary to reduce the quantity of heat transfer and also of friction losses. Both effects can be achieved by increasing the temperatures of the cooling medium and the lubricant. This leads to two effects: - reduction of fuel consumption - reduction of exhaust emissions.Both effects are valid even in the warming-up-phase as well as under normal operating temperature and are confirmed by the results of our experiments.