Abstract: To ensure that the coolant inlet temperature of the motorcycle radiator is within a controllable range, a motorcycle cooling system was taken as the research object. Basic experimental parameters of the cooling system were collected through component flow resistance testing, water pump performance testing, engine thermal balance testing, and radiator heat transfer performance testing, providing boundary inputs for flow rate analysis of the cooling system and radiator coolant inlet temperature analysis. The analysis results show that through the match analysis of pump performance curve and cooling system flow resistance curve, the working flow rate of the water pump is 23.5 L/min when the engine speed is 9000 r/min. The series connection of flow meter and testing fixture in engine thermal balance test causes a slight increase in system resistance, and the cooling system flow rate is 22.5 L/min. The maximum operating power of the engine at a speed of 9000 r/min is 14 kW, with a heating power of approximately 7.1 kW. The simulated inlet coolant temperature of the radiator is 109 ℃, which does not meet the coolant temperature control target of less than 100 ℃. By optimizing the volute guide, air outlet, and increasing the height of the impeller by 6 mm and the width of the impeller by 5 mm, the inlet air volume of the radiator was increased from 126.7 g/s to 188.5 g/s, and the air velocity of the radiator core was increased from 6.1 m/s to 9.28 m/s. The improvement effect of air volume and air velocity was significant. After optimization, the inlet coolant temperature of the radiator is 96 ℃. The results of the vehicle thermal balance test show that the radiator inlet balance temperature, cylinder temperature, and oil temperature of the optimized design under the highest vehicle speed condition are 98, 149 and 114 ℃, respectively. Compared with the initial design, the temperatures are reduced by 13, 18 and 13 ℃, which verifies the effectiveness of the optimized design. The research results can provide theoretical guidance for evaluating the heat dissipation performance of the vehicle cooling system and optimizing of coolant temperature.