This Factory Service Repair Manual covers the Yanmar 3YM30, 3YM20, and 2YM15 marine diesel engines. These 4-stroke, water-cooled diesel engines are known for their robust construction and reliable performance in marine applications. The 3-cylinder configuration, indirect injection fuel system, and forced lubrication system contribute to their efficiency and durability. Specific models offer varying power outputs and displacements, ranging from the 2YM15 with 14.7 PS to the 3YM30 with 29.4 PS, making them suitable for a range of vessel sizes and operational demands. This comprehensive English-language manual provides essential information for maintaining and repairing your Yanmar marine diesel engine. It includes detailed sections on troubleshooting, repair procedures, routine maintenance schedules, and technical specifications, such as oil and coolant requirements. Wiring diagrams are also included to assist with electrical system diagnostics. By following the guidelines within this manual, owners and technicians can ensure optimal engine performance, longevity, and safe operation.