This repair service manual covers the Yanmar 3YM30, 3YM20, and 2YM15 marine diesel engines. These engines are engineered for reliability and performance in marine applications, featuring water-cooled, 4-cycle diesel technology with indirect injection. The 3YM30 delivers up to 28.7 HP, the 3YM20 up to 20.0 HP, and the 2YM15 up to 15.0 HP, making them suitable for a range of vessel sizes and operational demands. Their robust construction and efficient design ensure dependable power for cruising, sailing, and auxiliary propulsion. This comprehensive manual provides detailed information essential for the maintenance and repair of your Yanmar engine. It includes step-by-step repair procedures, critical specifications, clear illustrations, and guidance on disassembly, assembly, cleaning, and reinstallation. Coverage extends to lubrication, cooling system maintenance, and filter replacement. This resource is designed to assist owners, mechanics, and technicians in keeping these marine diesel engines in optimal working condition, ensuring longevity and peak performance.