This workshop service repair manual covers the Mercury Mariner 225 HP DFI Optimax outboard engine, part of the Optimax DFI Series. Engineered for reliable performance, this direct fuel injection (DFI) outboard delivers 225 horsepower and features a water-cooled system. While specific model years are not individually listed, this manual provides comprehensive information applicable across the Optimax DFI generation, focusing on the robust engineering and advanced fuel injection technology that define these engines. This manual is designed to be an indispensable resource for maintaining and repairing your Mercury Mariner 225 HP DFI Optimax. It details essential service procedures, routine maintenance schedules, troubleshooting guides, and technical specifications, including information on its CDI ignition system. Whether you are a boat owner, a professional mechanic, or a technician, this English-language guide will equip you with the knowledge needed to ensure optimal performance and longevity of your outboard engine.