The cooling system in a vehicle engine is a system that functions to maintain temperature. The role of the cooling system is to maintain the temperature so that it is in ideal conditions by utilizing the air around it which will carry hot air from the engine to prevent overheating. This Final Project aims to apply and modify the radiator cooling system on the supra x 125 motorbike. The process of applying the radiator cooling system to the supra x 125 motor is done by making a water jacket and connecting it to the radiator. Coolant circulation system uses an electric water pump. In cooling fluid circulation, two circulation variables are performed by regulating the power in the electric water pump. Both of these variables are when the temperature at the engine has reached 50oC, the digital thermostat power will flow electric current to the electric waterpump by 50% of the maximum power and when the engine temperature is 100oC, the power given to the electric waterpump is at 100% of the maximum power. The results of the application are obtained when the temperature is 50oC the flow velocity is 30 ml / sec. When the temperature reaches 100 oC the flow speed is 90 ml / sec. Circulating water will be cooled to the radiator by utilizing a gust of wind coming from the front. And it works continuously when the engine is on or used.