D Disruptions in the power supply often disrupt the operational stability of several sectors such as offices, industries, hospitals and various other vital facilities. efforts to overcome these disruptions require alternative power sources, one of which is a generator set (genset). in the process, the engine in the genset will emit heat so that a cooling system is needed to maintain the engine temperature in the genset from overheating. the cooling system in the genset is called a radiator which works by cooling the fluid from the engine. the purpose of this study was to test the radiator of a 150 kva capacity generator carried out at pt. x. data was taken by measuring the temperature of the incoming and outgoing water in the radiator, the temperature of the incoming and outgoing air in the radiator and the air velocity in the radiator. all data were measured according to the percentage of generator power (0%, 25%, 50%, 75% and 100%) which was loaded by the load bank. the function of the load bank in this study was to provide a power load to the genset. the test results showed that the radiator heat transfer rate at 0% and 100% generator load was 33351.73 w and 385506.72 w. the overall heat transfer coefficient value at 0% and 100% generator load is 2789.92 w/m2k and 5543.32. the heat transfer rate of the radiator tube at 0% and 100% generator load is 97.97 w and 785.55 w. the heat transfer rate of the radiator fin at 0% and 100% generator load is 358.94 w and 2878.15 w. the conclusion of this study is that the increasing percentage of generator power load, the value of the heat transfer rate and the overall heat transfer coefficient value in the radiator increases.