Abstract: Diesel engine fuel treating means which heats the fuel flowing from the fuel tank to the engine also furnishes heat to the fuel in the tank, provides for removal of contaminants, and inhibits gelling and wax solidification. In some embodiments the heating device is incorporated in the fuel tank, and includes a fuel filter intimately associated with the treating device but accessible outside the tank. In another embodiment the treating device is located outside the tank and includes two fuel heating circuits, one for fuel flowing to the engine and the other for preheating the main fuel supply in the tank. A third embodiment has an axial tubular member which conducts heated and filtered fuel from a top-mounted spin-on filter back through the heating chamber in a second pass and also forms a clamping device for a removable cover and an attaching and fluid coupling device for the filter.