Designing an efficient cooling system with low power consumption is of high interest in the automotive engineering community. Heat generated due to the propulsion system and the on-board electronics in ground vehicles must be dissipated to avoid peak component heat loads. In addition, proper thermal management will offer improved system durability and efficiency while providing a flexible, modular, and reduced weight structure. Traditional cooling systems are effective but they typically require high energy consumption which provides motivation for a paradigm shift. This study will examine the integration of passive heat rejection pathways in ground vehicle cooling systems using a thermal bus. Potential solutions include heat pipes and composite fibers with high thermal properties and light weight properties to move heat from the source to ambient surroundings. An initial case study focuses on the integration of heat pipes in a cradle (thermal connector between heat load and bus) to transfer heat from the thermal load (e.g., internal combustion engine, electric motor, battery pack, power electronic, etc.) to the heat exchanger. A mathematical U-shaped pulsating heat pipe model is developed to numerically describe the thermal behavior of heat pipe based cradle. Simulation results indicate that the heat dissipation rate is significantly influenced by heat pipe length, diameter and the temperature difference between the heat load and the bus. The integration of this heat pipe based cradle within an active / passive thermal bus will be demonstrated in future work.