This Workshop Service Manual covers the Mercury Marine Mariner Optimax outboard engines manufactured from 1999 onwards, specifically for the Optimax 135/150 DFI generation with serial numbers OG590000 and above. These engines feature a 60° Vee V-6 configuration, a 2-stroke direct fuel injection (DFI) system, and are available in 135 HP and 150 HP variants, with a displacement of 153 cubic inches (2508 cc). Engineered for reliability and performance, the Mariner Optimax series represents advanced marine propulsion technology designed for a wide range of boating applications. This comprehensive English-language manual provides detailed, step-by-step instructions and diagrams to assist both DIY enthusiasts and experienced mechanics. It covers essential maintenance procedures, including service intervals for components like spark plugs, impellers, and gearcase oil, as well as the oil injection system. The manual also delves into the repair and troubleshooting of critical systems such as the electrical (ignition, charging, starting), fuel (pump, DFI), cooling, and drivetrain components, including various gear housing types. Additionally, it addresses clamp swivel brackets, power trim, control linkage, and emissions systems, ensuring thorough coverage for maintaining and repairing these powerful outboard engines.