The Mercury Optimax, produced between 1998 and 1999, represents a significant advancement in marine engine technology. These engines are characterized by their Direct Fuel Injection (DFI) systems, DOHC valve trains, and multi-point sequential electronic fuel injection, delivering robust performance with horsepower ratings of 135 HP and 150 HP. Designed for reliability and efficiency, the Optimax series offers a powerful and dependable propulsion solution for a variety of watercraft, embodying Mercury's commitment to engineering excellence. This comprehensive service, repair, and workshop manual provides essential information for maintaining and troubleshooting your Mercury Optimax engine. It covers critical areas such as lubrication, cooling system service, and detailed maintenance schedules. With clear instructions and technical specifications, this English-language manual is an indispensable resource for owners, mechanics, and technicians alike, ensuring optimal performance and longevity of the engine.