This document pertains to the Mercury Mercruiser 181 CID engine, an inline 4-cylinder marine powerplant. Featuring a displacement of 181 cubic inches, a bore of 4.00 inches, and a stroke of 3.48 inches, this engine is designed for reliable performance on the water. It operates with a carbureted fuel system and a points ignition system, producing approximately 130 horsepower. The engine is equipped with a closed cooling system, which can be either raw water or freshwater cooled, and utilizes a water-cooled exhaust manifold for efficient operation. This engine is paired with a sterndrive transmission offering forward, neutral, and reverse gears. This Factory Service Repair Manual in English provides comprehensive guidance for the maintenance and repair of the Mercury Mercruiser 181 CID engine. It covers essential procedures, technical specifications, and troubleshooting information necessary for optimal performance and longevity. Owners and technicians will find detailed instructions on various aspects of engine care, including oil capacity and recommended oil types, along with information on spark plug gap and timing advance. The manual serves as an indispensable resource for ensuring the continued reliability and proper functioning of this marine engine.