Two endurance tests were completed on a diesel engine in the Allis Chalmers Engine Division at Harvey, Illinois. The two tests included a 500 hour baseline test with #2 diesel fuel and a 600 hour test with a 50/50 (v/v) blend of alkali refined sunflower oil and #2 diesel fuel. A continuous test cycle of three minutes at high idle and 10 minutes at peak torque was used. There were no significant problems with engine operation during the baseline test. However, problems were experienced while operating on the blended fuel. While using the blended fuel (1) there was abnormal carbon buildup on the injection nozzle tip, (2) the nozzle opening pressure dropped 10-15%, (3) the injection nozzle needles stuck, (4) there was excessive carbon buildup on the intake ports, (5) operation problems of the turbocharger were observed, and (6) piston ring sticking problems were experienced.