This manual covers the Hino N04C, W04D, and W04C-T diesel engines, commonly found in the Hino 300 Series trucks. These 4.0L and 3.8L four-cylinder, in-line, four-cycle engines are designed for reliable performance in commercial applications. The engines feature water-cooling, overhead valve (OHV) configurations, and include turbocharged variants for enhanced power and efficiency. This comprehensive guide is intended to support the upkeep and repair of these robust Hino powertrains. This workshop service repair manual provides detailed instructions and technical specifications essential for maintaining and repairing the specified Hino engines. It covers a wide range of topics including general information, safety precautions, tightening torques, and specific maintenance procedures for various engine systems such as the fuel, cooling, lubrication, starting, and charging systems. Additionally, the manual includes troubleshooting guides and information on special service tools, making it an invaluable resource for professional mechanics and owner-operators alike.