This manual covers the Yanmar 4JHE, 4JH-TE, 4JH-HTE, and 4JH-DTE marine diesel engines. These 4-cylinder engines, with approximately 1.8L displacement, are designed for marine propulsion. Variants include naturally aspirated (4JHE) and turbocharged (4JH-TE, 4JH-HTE, 4JH-DTE) configurations, offering a power range typically between 40-70 HP. They utilize direct injection and can be configured for raw water or heat exchanger cooling systems, paired with an inboard marine gearbox. Yanmar engines are recognized for their robust engineering and reliability in demanding marine environments. The purpose of this English-language service shop repair manual is to provide comprehensive guidance for the servicing, repair, and preventative maintenance of these Yanmar marine diesel engines. It details essential information including technical specifications, fluid capacities, recommended service intervals for oil and filter changes, and a troubleshooting guide to address common issues. This manual is an indispensable resource for owners, mechanics, and technicians seeking to ensure the optimal performance, longevity, and safe operation of their Yanmar propulsion systems.