This manual covers the Yanmar YSE8 and YSE12 marine diesel engines, designed for marine applications. These engines are known for their robust construction and reliable performance, providing dependable power for a variety of marine vessels. The YSE8 offers approximately 8 horsepower, while the YSE12 provides around 12 horsepower, both utilizing compression ignition for efficient operation. These engines typically feature raw water or freshwater cooling systems to ensure optimal operating temperatures in demanding marine environments. This comprehensive 3-manual set serves as an operator, service, repair, and shop manual, providing detailed guidance in English. It covers all routine maintenance, service procedures, and repair procedures with step-by-step instructions and includes helpful illustrations and wiring diagrams. The manual is designed for ease of use and is compatible with PC, Mac, tablets, and smartphones, ensuring accessibility for owners and technicians alike to maintain and repair their Yanmar marine diesel engines effectively.