This service repair manual covers Mercury Mercruiser GM 4 Cylinder engines, typically featuring inline 4-cylinder configurations with displacements around 3.0L. These engines are known for their robust engineering and reliability, designed for various marine applications. Depending on the specific model and year, power output can range from approximately 135 to 150 horsepower, utilizing either carbureted or fuel-injected fuel systems and distributor or distributorless ignition. Cooling systems can be raw water or closed cooling, and lubrication typically requires SAE 25W-40 marine oil. This comprehensive English-language manual provides essential information for owners, mechanics, and technicians. It details scheduled maintenance procedures, including recommended intervals for oil changes, spark plug replacement, and impeller service, as well as engine flushing protocols for saltwater use. The manual also covers fluid capacities, transmission specifications, and technical data for maintaining optimal performance and longevity of your Mercruiser engine. Troubleshooting guidance and detailed technical specifications are included to assist with diagnostics and repairs.