This workshop service manual covers the Mercury Mariner 90 HP 3 Cylinder outboard engine manufactured between 1987 and 1993. This robust 3-cylinder, water-cooled engine is designed for reliable performance on the water, featuring a carbureted fuel induction system and CDI ignition for efficient operation. Its engineering emphasizes durability and consistent power output, making it a dependable choice for various marine applications. The outboard lower unit provides efficient propulsion, with a drive system designed for optimal maneuverability and performance across its operating RPM range. This comprehensive manual provides detailed instructions and specifications essential for the maintenance, repair, and overhaul of your Mercury Mariner outboard. It covers critical procedures, including recommended service intervals, fluid types, and component specifications. Owners, technicians, and mechanics will find valuable information on troubleshooting, diagnostic procedures, and technical data necessary to keep this engine operating at peak performance and reliability. The manual is presented in English and serves as an authoritative guide for all service-related tasks.