Abstract: An improved fuel temperature control system is disclosed for attachment to a diesel engine. The control system comprises a fuel tank, an injection pump and a transfer pump along with associated fuel lines. The transfer pump is designed to draw fuel out of the fuel tank and route it to the injection pump. In the injection pump, a portion of the fuel is directed to the cylinders of the engine while the unused portion is returned via a return line to the fuel tank. In addition to the above, a temperature control means is positioned across the fuel supply line between the transfer pump and the injection pump. This temperature control means contains a temperature sensor interconnected to a temperature compensator valve. The temperature sensor is capable of sensing the temperature of the fuel as it flows through the fuel supply line while the temperature compensator alters the direction of flow of the fuel in response to commands from the temperature sensor.