This manual covers the YM Series marine diesel engines, specifically models 3YM30, 3YM20, and 2YM15. These engines are renowned for their robust engineering, reliability, and suitability for a wide range of marine applications. The 3YM30 offers a power output of 20.2 kW (27.1 HP), the 3YM20 provides 14.2 kW (19.0 HP), and the 2YM15 delivers 10.3 kW (13.8 HP), all at 3200 rpm. These engines feature indirect freshwater cooling, glow plug ignition, and electric starting systems, ensuring efficient and dependable operation in demanding marine environments. The YM Series Service and Repair Manual provides comprehensive guidance for owners, mechanics, and technicians. This English-language manual details essential maintenance procedures, including recommended oil types and capacities, coolant specifications, and typical oil change intervals of 100 hours or annually. It also includes troubleshooting sections, wiring diagrams, technical specifications, and service standards to facilitate effective maintenance and repair. By following the step-by-step instructions within this manual, users can ensure the optimal performance and longevity of their YM Series engines.