modified locomotive engine cooling systems are designed to reduce engine emissions and improve engine efficiency . the systems include separate main engine and turbocharger aftercooler coolant loops that are joined when extra engine cooling is required . studies determined that by reducing and optimizing the aftercooler loop coolant flow rate , the amount of heat transfer from the engine inlet air to the radiator cooling air could be increased . thus , a significant increase in aftercooling could be obtained by reducing the coolant temperature at the inlet of the aftercooler and this could be accomplished by reducing the rate of flow of coolant in the aftercooler loop . this improvement and how it may be applied in practice are fundamental features of the cooling system and method .