Abstract: An automobile engine coolant heater for connection to hoses of the engine coolant systems has a elongated cylindrical jacket portion defining a coolant flow path from an inlet at one end to an outlet at the other end. A metal sheathed heating element is located within the flow path and includes elongated heat generating leg portions. A thermostat for regulating operation of the heating element is mounted in heat conductive relationship on a flattened exterior portion of the jacket. An elongated, open ended metallic heat transfer tube provides a thermal bridge between the heating element leg portions and the interior surface of the flattened portion of the jacket. The heat transfer tube and heating element legs are in axial alignment with the longitudinal axis of the jacket to minimize flow resistance through the flow path. The heat transfer tube is brazed to the leg portions and to the flattened portion.