This manual covers the YANMAR YM Series diesel engines, including the 2YM15, 3YM20, and 3YM30 models. These engines are engineered for reliability and performance in marine applications, featuring robust diesel technology. The 2YM15 offers 14.1 PS, the 3YM20 provides 20.0 PS, and the 3YM30 delivers 29.0 PS, all operating at 3600 RPM. They are designed with a focus on durability and efficient operation, suitable for various vessel types. The purpose of this English-language Operation Manual is to provide comprehensive guidance for the operation, maintenance, and troubleshooting of your YANMAR YM Series engine. It details essential procedures such as daily checks, scheduled maintenance at specified intervals, lubrication requirements for engine oil and marine gear oil, and coolant specifications. The manual also includes important safety precautions, engine startup and control procedures, and instructions for long-term storage. A troubleshooting guide is provided to assist in diagnosing and resolving common issues, ensuring the continued optimal performance and longevity of your engine.