This Parts Manual/Catalog provides comprehensive information for the Caterpillar D333C engine, identified by serial number prefix 66D. The D333C is a robust diesel engine known for its reliability and engineering quality, commonly configured as an inline 6-cylinder unit. Typical specifications include a bore of 4.5 inches, a stroke of 5.5 inches, and a displacement of 525 cubic inches (8.6 Liters), with horsepower generally ranging from 100-200 HP depending on the application. This manual is designed to support the maintenance, repair, and rebuilding of this essential engine. The scope of this English-language manual is extensive, covering all aspects of the D333C engine. It includes detailed illustrations, diagnostic procedures, and information on electrical systems, wiring diagrams, and instrumentation. Maintenance coverage is thorough, detailing service intervals and fluid recommendations. The manual is structured with numbered, step-by-step instructions to assist owners, mechanics, and technicians in effectively maintaining and repairing their Caterpillar D333C engine, ensuring its optimal performance and longevity.