An experimental investigation has been carried out to analyze the performance and emission characteristics of a compression ignition engine fueled with preheated Karanja oil and its blends (10%, 20%) with diesel. Viscosity of unheated 10%, 20% blend, and preheated oil is found suitable for diesel engines. Preheating is done to reduce the viscosity of Karanja oil using an electric heater. The parameters examined include brake thermal efficiency, brake specific fuel consumption, brake specific energy consumption, emissions of CO, CO2, HC, and NOx for blended and preheated oil. Significant improvements have been marked in the performance parameters of the engine as well as exhaust emissions when lower blends of Karanja oil were used.