The components in a hybrid electric vehicle (HEV) powertrain include the battery pack, an internal combustion engine, and the electric machines such as motors and possibly a generator. These components generate a considerable amount of heat during driving cycles. A robust thermal management system with advanced controller, designed for temperature tracking, is required for vehicle safety and energy efficiency. In this study, a hybridized mid-size truck for military application is investigated. The paper examines the integration of advanced control algorithms to the cooling system featuring an electric-mechanical compressor, coolant pump and radiator fans. Mathematical models are developed to numerically describe the thermal behavior of these powertrain elements. A series of controllers are designed to effectively manage the battery pack, electric motors, and the internal combustion engine temperatures. These controllers regulate the refrigerant compressor, coolant pump, and cooling fans to minimize the temperature fluctuations while reducing the overall cooling system power consumption. Simulation results for assault and convoy escort driving cycles are presented to show that the controllers meet the powertrain heat removal requirements. The battery core temperature can be tracked to within 0.8 °C of the target value, the internal (stator) temperature of electric motors can be maintained within 1.1 °C of the desired value. The coolant temperature at engine's outlet exhibited a 0.4 °C error range from the prescribed target value of 90 °C. The overall auxiliary power consumption of the cooling system is reduced by 45% when compared to a conventional cooling control method.