In Test Bench Facility of PT. PAL Indonesia, Secondary Circuit Cooling is used to keep the inlet temperature of water transferred from the main engine through a heat exchanger to the primary circuit in the standard condition of 32°C. Unfortunately, the secondary circuit cooling system cannot maintain the high temperature generated by the primary circuit. Therefore, controlling the water-cooling flow rate through a heat exchanger is important to obtain a standard temperature. This research developed an intelligent secondary circuit cooling system to control water flow rate using speed variation of pump impeller with Fuzzy Logic. The control methods were tested using a prototype in model scale at a ratio of 1:7. The system works due to the temperature difference between the inlet and outlet heat exchanger on the cold side, Res Militaris, vol.13, n°2, January Issue 2023 5239 which improved with the application of fuzzy control. The error was reduced by 47.3% from the existing condition of 1.08. Furthermore, Fuzzy logic control contributes to keeping inlet temperature close to 32°C. This performance showed that this system can be used to improve the heat exchange from the main engine.