Failure of the purification process in Fuel Oil Purifier No. 2 reduces the quality of fuel supplied to the main engine, resulting in incomplete combustion, lower engine efficiency, and increased component wear. This study aims to identify the causes of purification failure, analyze its impact on fuel quality and main engine performance, and propose corrective and preventive measures. A descriptive qualitative method was used, with data collected through direct observation during sea practice (PRALA), interviews with engine officers and crew, documentation, and literature review. The results show that purification failure was caused by fuel heating temperatures below the normal operating range (80–85°C) due to carbon deposits on the boiler burner, sludge accumulation causing bowl disc overflow, and damaged electric motor bearings and V-belts that prevented the purifier from reaching its optimum rotational speed. These conditions reduced the effectiveness of separating water and impurities from the fuel, allowing contaminated fuel to enter the main engine. As a result, combustion became incomplete, engine efficiency declined, and the risk of engine component wear increased. The study concludes that successful fuel purification depends on maintaining the correct operating temperature, ensuring the reliability of purifier components, and implementing proper maintenance procedures. Preventive measures include consistent application of the Planned Maintenance System (PMS), routine cleaning of the boiler burner and bowl disc, regular monitoring of operating temperature, timely replacement of worn bearings and V-belts with manufacturer-approved spare parts, and continuous monitoring of fuel quality to ensure reliable main engine performance.