The scheme of the cooling system is considered, which can be the basis for creating the most efficient cooling systems for IC engines of any purpose. It is assumed that the use of any other scheme is devoid of a rational basis. The scheme consists of two connected circulation circuits, in one of which the coolant flow rate is an order of magnitude less than in the second. The engine is included in a circuit with increased coolant flow. All heat exchangers are in the second circuit. Rules for the formation of such systems are formulated. The basis of the method for calculating such systems is considered. It is indicated that the flow rate through each heat exchanger must be determined by calculation to ensure the maximum efficiency of the cooling system. The considered scheme allows to provide the maximum possible depth of charge air cooling, if its temperature is not specified, or to ensure the minimum cost and compactness of the cooling system if this temperature is known. The scheme allows regulating the temperatures of the cooling fluids of the system with all kinds of changes in the engine operating conditions and the ambient temperature.