The Mercury Mercruiser MCM 3.0L and 3.0LX models, powered by GM 4-cylinder engines with a displacement of 3.0 liters, represent robust marine propulsion systems designed for reliability and performance. These engines, featuring a MerCarb 2-barrel carburetor and available in seawater or closed-cooled configurations, are engineered for a wide range of marine applications. This manual covers models with applicable serial numbers OC856451 and above for the 3.0L, and OC868143 and above for the 3.0L/3.0LX, ensuring precise identification for maintenance and repair. This comprehensive Service Repair Manual provides detailed guidance for owners and professionals alike. It covers essential maintenance procedures, diagnostic troubleshooting, technical specifications, and repair strategies, including restoration and rebuilding. With information on starting, ignition, charging, instrumentation, and wiring diagrams, this workshop guide equips users with the knowledge to maintain, service, and repair their Mercury Mercruiser MCM 3.0L / 3.0LX engines effectively. The manual is designed for both DIY enthusiasts and professional technicians, ensuring optimal performance and longevity of the marine drive system.