Due to higher diesel fuel prices, operators of heavy trucks, especially large fleets, are looking for ways to increase fuel economy. One way to increase fuel economy is to reduce the “parasitic” horsepower losses on the engine. Today's mechanically driven cooling fans are a large draw on the engine horsepower. The function of the Thermal Kits is to provide auxiliary engine cooling and air conditioning condenser cooling with electric fans and electric water pumps. This paper details the application of Thermal Kits to various heavy duty truck applications, including control system development and vehicle integration. Fuel economy improvements from these Kits in various applications are currently being independently validated and should be available by the 2006 Commercial Vehicle Conference.