This paper presents the experimental investigation of a two-phase closed loop. The experimental setup consists of an evaporator and a condenser connected by two insulated tubes. Using water as a working fluid, the experiments were conducted to evaluate the performance of a thermosyphon: the effects of fill charge ratio, the condenser jacket coolant inlet temperature and the mass flow rate. Finally, the results show that the optimal fill charge ratio is between 7% and 10%, the cooling system has the optimal performance when controlling the condenser jacket water temperature and flow rate at 5 °C and at 0.7 l/min respectively. System, loop, evaporator, vapor line, condenser, and liquid line thermal resistances analysis is directed additionally to the pressure and temperature evolutions for the better understand of the main parameters affecting the cooling system performance.