Abstract: A fuel injection system having an air supply and a fuel injection spray valve furnishing an air-fuel mixture to an internal combustion engine has a fuel heating device for heating the fuel just prior to spraying from the valve to enhance fuel-air mixing, the heater having a housing comprising a pair of stiffly compressible housing elements clamped in sealing relation to each other for capturing a flat ceramic heating device of positive temperature coefficient of resistivity between the compressible housing elements, the elements each having a central opening and a spiral groove therein cooperating to form a chamber holding the heating device and for guiding fuel through the grooves in heat-transfer relation to the disc along spiral paths extending along each flat side of the heating disc, the housing having terminals sealed therein for electrically engaging opposite sides of the heating disc.