This manual covers the Caterpillar NTA-855-L4, a robust diesel engine from the 855 Series. This inline 6-cylinder engine features a displacement of 855 cubic inches (13.9 Liters), a bore of 5.4 inches (137 mm), and a stroke of 6.0 inches (152 mm). It is equipped with a turbocharged and aftercooled (TA) aspiration system and a mechanical fuel injection (PT Pump) system, all managed by a water-cooled system. Power output is variable, typically ranging from 270 to 400 horsepower, with torque output also dependent on the specific application. Designed for demanding industrial and heavy-duty applications, this engine is known for its durability and performance. This Service Repair Manual, provided in English and available in digital or print formats, is an essential resource for maintaining and repairing the Caterpillar NTA-855-L4 engine. It details critical maintenance procedures, including oil and cooling system capacities, recommended engine oil specifications, oil change intervals, and filter replacement guidelines. The manual also provides technical specifications, troubleshooting information, and safety guidelines to ensure the engine operates at peak performance and longevity. This comprehensive guide is intended for owners, mechanics, and technicians seeking to understand and service this powerful diesel engine.