Abstract: Fuel for a diesel engine is fed to the engine through a small float tank provided with a fuel heater. A cooling unit is employed to cool overheated fuel recycled from the engine. A temperature controlled valve is utilized to divert recycled fuel from the cooling unit through the float tank and back to the engine if the recycled fuel is sufficiently cool. The fuel heater, cooling unit and valve are adapted to optimize fuel temperature based on engine performance design.Water, propane, LPG, etc. also may be injected into the engine along with the diesel fuel to improve the combustion process and fuel economies.