The cooling system is necessary in any internal combustion engine. If no cooling system is provided, parts would melt from the heat of burning fuel and the piston would expand so much they could not move in the burning. In this paper, the design engine is made of the cast iron alloy and it can be studied on engine water cooling system. The cast iron engine head can get over heat at high temperature because the thermal conductivity of cast iron is not good. So, the design engine head is necessary of increasing the cooling efficiency and it must be also needed to increase water tube and cooling fins more than original radiator. The rate of circulation of water coolant, is determined from the quantity of heat received by the cooling system. In the radiator design calculation, design amount of heat to the coolant, heat dissipation surface areas, radiator face area and radiator design selection are described.