This workshop service repair manual covers Mercury Marine OptiMax engines, specifically those with serial numbers 0T801000 and above. These direct fuel injection, water-cooled engines are available in 3-cylinder configurations with displacements of 1.5L and power outputs ranging from 75 HP to 125 HP, including models such as the 75 OptiMax, 90 OptiMax, 115 OptiMax, 115 Pro XS, and 125 OptiMax. Engineered for reliability and performance, these engines are designed for a variety of marine applications, offering advanced features for efficient operation. This comprehensive manual is designed for both do-it-yourself enthusiasts and experienced mechanics. It provides detailed information on all aspects of engine maintenance, repair, and troubleshooting. Key areas covered include the fuel system, injection system, ignition system, cooling system, gear housing, and power trim. Additionally, the manual includes technical specifications, detailed illustrations, wiring diagrams, and information on diagnostic systems like CDS and PCM, ensuring that owners and technicians have the resources needed to maintain these engines in optimal condition.