The YANMAR 4LHA-ST/DT/HT series represents a line of robust Marine Diesel engines, engineered for reliability and performance in demanding marine environments. These 4-cylinder, vertical, 4-cycle engines feature a 3.455-liter displacement and are water-cooled, with certain variants offering turbocharged aspiration for enhanced power output. Their design prioritizes durability and efficient operation, making them a trusted choice for a variety of marine propulsion applications. This Workshop Service Manual and Operator's Manual provides comprehensive guidance for maintaining and repairing the YANMAR 4LHA-ST/DT/HT engines. It covers essential areas including detailed disassembly and re-installation procedures, system diagnostics, and troubleshooting. The manual is designed to assist both DIY enthusiasts and experienced mechanics in understanding and servicing the engine's internal components, fuel system, air management, lubrication and cooling systems, electrical and control systems, and more, ensuring optimal performance and longevity.