Fan-radiator cooling systems for diesel engines have experienced only minor changes in basic design since their inception. However, the increase in power output over decades of development of the engine has forced the cooling system to become larger, more complex and more expensive. Problems of fan noise, low system efficiency, durability and safety persist. The thermodynamic basis for the design of a new cooling system for heavy-duty diesel engines is presented in this paper. The new system consists of an exhaust gas turbine driving a high-speed ducted fan to provide cooling air for engine and vehicle heat exchangers. Since the turbo-fan is not mechanically connected to the engine, the components can be located in more convenient places that favor vehicle aerodynamics, operator visibility and operational safety.