The paper describes engine modifications, which are proposed to provide a means to overcome the adverse effect of sunflower oil fuel on diesel engines' longevity. The proposed system consists of a dual fuel system and fuel preheater. The dual fuel system was designed to eliminate engine conditions that are responsible for the majority of the problems associated with the use of sunflower oil fuel. Specifically, the dual fuel system will (1) prevent the operation of an engine on alternative fuels at low-load, low-speed conditions, (2) reduce the exposure time of the fuel injection system to the sunflower oil at the excessively high temperature conditions during the transition process from high to light loads, (3) eliminate the conditions (such as cold start-up) at which the fuel temperature is too low for acceptable atomization, and (4) eliminate the exposure of the fuel injection system to sunflower oil during the shut-down period.A fuel preheater was added to the diesel engine fuel system to maintain an optimum inlet fuel temperature. An alternative approach to reduce the effect of the high viscosity of plant oil fuels on fuel flow is the application of an additional transfer pump prior to the high pressure injection pump.