This manual covers the Mercury Mariner 40 HP 4-stroke outboard engine, produced between 1999 and 2003. This engine features a 3-cylinder inline configuration with a displacement of 737 cc (45 cu in), delivering 40 HP at 5500 RPM. It is equipped with a carbureted fuel system, a Forward-Neutral-Reverse transmission with a 2.0:1 gear ratio, and a water-cooled system. Designed for reliable performance on the water, this outboard is engineered for a variety of boating applications. The purpose of this Service Repair Manual is to provide comprehensive guidance for the maintenance, repair, and servicing of your Mercury Mariner 40 HP outboard. It includes detailed procedures for lubrication, cooling system maintenance, ignition system servicing, and spark plug replacement, along with specifications for fuel, oil, and electrical systems. This manual is an essential resource for owners, mechanics, and technicians seeking to ensure the optimal performance and longevity of their engine.