Biodiesel is a renewable and environmentally friendly alternative fuel that can be used in Diesel engines with little or no modification. Low cost feedstocks, such as waste oils. used cooking oil and animal fats, are important for low cost biodiesel production. The objective of this study was to investigate the engine performance and the road performance of biodiesel fuel originated from used cooking oil in a Renault Megane automobile and four stroke, four cylinder, F9Q732 code and 75 kW Renault Megane Diesel engine in winter conditions for 7500 km road tests in urban and long distance traffic. The results were compared to those of No. 2 Diesel fuel. The results indicated that the torque and brake power output obtained during the used cooking oil originated biodiesel application were 3-5 % less then those of No. 2 Diesel fuel. The engine exhaust gas temperature at each engine speed of biodiesel was less than that of No. 2 Diesel fuel. The injection pressures of both fuels were similar. Higher values of exhaust pressures were found for No. 2 Diesel fuel at each engine speed. As a result of the No. 2 Diesel fuel application, the engine injectors were normally carbonized. After the first period, as a result of winter conditions and insufficient combustion. carbonization of the injectors was observed with biodiesel usage. As a result of the second period, since the viscosity of the biodiesel was decreased, the injectors were observed to be cleaner. Also. no carbonization was observed on the surface of the cylinders and piston heads. The catalytic converter was plugged because of the viscosity in the first period. At the second period, no problem was observed with the catalytic converter. (C) 2004 Elsevier Ltd. All rights reserved.