The radiator surge tank is only on the 6.5L Diesel engine and takes the place of the coolant reservoir found on gasoline engines. The primary function of the surge tank is to allow air bubbles to escape from the cooling system and to allow proper cooling temperatures. The low coolant level sensor is mounted on the side of the surge tank and is serviced by replacing the surge tank as a complete assembly. For electrical diagnosis, refer to Heater in Electrical Diagnosis.