This document provides comprehensive service information for the Mercury Mariner 225 HP DFI Optimax outboard engine. Engineered as a robust 2-stroke, water-cooled unit with Direct Fuel Injection (DFI) technology, this engine is designed for reliable performance on the water. Its 225 horsepower output, combined with a propeller drive system, makes it suitable for a variety of marine applications where power and efficiency are paramount. The Optimax series is known for its advanced engineering and dependable operation, ensuring a superior boating experience. This Factory Service Repair Manual is an essential resource for maintaining and repairing your Mercury Mariner outboard. It covers a wide range of topics, including detailed maintenance procedures, troubleshooting guides, technical specifications, and critical safety information. Whether you are performing routine servicing, such as oil changes with Quicksilver Premium Plus 2-Cycle Oil or ensuring the correct 91 octane fuel is used, or undertaking more complex repairs, this manual provides the necessary instructions and data. It is designed to assist owners, technicians, and mechanics in keeping the engine in optimal condition, ensuring its longevity and performance.