This paper reviews the impact of using biodiesel fuel containing large amounts of raw material components on engine performance in an agricultural tractor. If a fuel containing abundant methanol, a raw material component, is used, the engine output decreases; presumably due to the drop in fuel injection. Accordingly, it emerged that the engine’s original fuel consumption could not be maintained as methanol vapor was generated from the fuel and accumulated in the fuel pipe. Moreover, the engine was operated for 700 hours using a fuel containing abundant triglyceride, which, in itself, is a raw material fat residue for a new tractor, regularly inspecting and servicing as specified by the tractor manufacturer and using the electrical dynamometer. Consequently, the power output from the power take-off shaft（hereinafter referred to as “PTO”） decreased by 0.4 to 1.2kW from the value before the start of the operation, the specific fuel consumption (hereinafter referred to as “SFC”) increased by 7 to 23g/kWh and the carbon monoxide (CO) and black smoke concentrations increased significantly. Based on the disassembly and adjustment of engine parts after the operation, this phenomenon is considered attributable to the reduction in exhaust valve clearance accompanying the wear of the valve seat, which may occur, even in the middle of the operation with diesel fuel.