Abstract: A fuel pre-heater is used for heating the fuel for internal combustion engines, especially diesel engines. The pre-heater has an elongate cylindrical outer container housing an inner, concentric tube so as to provide an annular chamber between the two. A fuel tube, formed into a coil extends the length of the annular chamber, with its inlet and outlet exiting through the ends of the container. Heating medium inlet and outlet nipples for the container are arranged tangentially, at opposites ends of the container and oriented in opposite directions. The heating medium inlet and outlet are connected into the coolant system of the internal combustion engine while the fuel inlet and outlet are connected into the fuel line leading to the fuel injectors or carburetor of the engine. The pre-heater produces with its long path and counterflow pattern highly efficient heat transfer from the cooling medium to the fuel.