This manual covers the Yanmar 3YM30, 3YM20, and 2YM15 marine diesel engines. These engines are known for their robust construction and reliable performance in marine environments. Designed for a variety of maritime applications, they incorporate essential systems such as a cooling water system, lubrication system, and fuel injection equipment, ensuring efficient and dependable operation. The engines feature a 3-cylinder configuration for the 3YM30 and 3YM20 models, and a 2-cylinder configuration for the 2YM15. This comprehensive service repair manual, written in English, provides detailed guidance for the maintenance and repair of your Yanmar marine diesel engine. It includes extensive information on inspection and adjustment, disassembly and reassembly procedures, troubleshooting common issues, and technical maintenance. The manual also covers service standards, tightening torques, and electrical system wiring diagrams. With step-by-step operations, diagnosing procedures, and clear illustrations, this resource is an invaluable tool for owners, mechanics, and technicians seeking to maintain the optimal performance and longevity of their Yanmar engines.