This document pertains to the Mercury Mariner 40 HP 4 Stroke Outboard motor. Designed as a robust and reliable marine propulsion system, this outboard motor is engineered for a variety of watercraft, offering dependable performance for recreational and professional use. Its 4-stroke design ensures efficient operation and reduced emissions, while the 40 horsepower output provides ample power for a range of boating applications. The motor features a water-cooled system for optimal operating temperatures and typically employs fuel injection and a CDI ignition system for consistent power delivery. This Workshop Service Manual provides comprehensive guidance for the maintenance, repair, and technical understanding of the Mercury Mariner 40 HP 4 Stroke Outboard. It covers essential procedures for routine servicing, including lubrication and cooling system maintenance, as well as detailed information on engine specifications, electrical systems, and troubleshooting. The manual is intended for owners, technicians, and mechanics, equipping them with the necessary knowledge to ensure the longevity, efficiency, and optimal performance of the outboard motor.