The YANMAR 4LH-TE, 4LH-HTE, 4LH-DTE, and 4LH-STE marine diesel engines represent a line of robust, in-line 4-cylinder powerplants designed for commercial and light-duty marine applications. These engines feature turbocharged aspiration, with some variants including intercooling, delivering power outputs typically ranging from 100 to 130 horsepower (74-96 kW). With a displacement of 3.965 liters, a bore of 104 mm, and a stroke of 115 mm, these engines are engineered for reliability and performance in demanding marine environments, incorporating a reduction and reversing marine gear for efficient propulsion. This service, repair, and workshop manual provides comprehensive guidance for the YANMAR 4LH-TE, 4LH-HTE, 4LH-DTE, and 4LH-STE marine diesel engines. It covers essential maintenance procedures, detailed troubleshooting steps, critical technical specifications, and important safety guidelines. The manual is designed to assist owners, mechanics, and technicians in effectively maintaining, diagnosing, and repairing these engines, ensuring optimal performance and longevity.