Abstract: The fuel system services the internal combustion engine of an automobile or similar vehicle and includes a fuel heater disposed intermediate the carburator and fuel pump of the system. Fuel passing through the heater is heated to a desired temperature, by heat derived from a counter-flow circulation through the heater of hot water from the engine's cooling system, effective to increase the efficiency of the engine and to reduce exhaust-pollution. Operation of the heater is automatically and continuously regulated by control means which detects and is responsive to the temperature of the fuel passing downstream from the heater to the carburator. Cooling means are provided within that part of the fuel system intermediate the heater and the fuel pump to minimize heat-transfer in an upstream direction through the system, and to thus minimize the possibility of "vapor-lock" of the fuel pump.