Abstract: Improvements in fuel heating apparatus for internal combustion engines utilizing hot water from the engine cooling system as the heat exchanging medium; improvements in hydrocarbon fuel heaters and preheaters for internal combustion engines utilizing a heat exchanging jacket or sleeve on the feed line between the fuel pump and carburetor; simplified, improved heat exchangers for preheating fuel fed to an internal combustion engine employing a heat exchanging jacket on the feed line between the fuel pump and the carburetor with but a single flow passage circulating hot water from the engine block cooling system form the bleed to the heater or after the heater before the water pump to and from the jacket.