Protect your investment in diesel power and confidently extend drain intervals with our top-grade synthetic diesel oil. AMSOIL Signature Series Max-Duty Synthetic Diesel Oil delivers 4X better cold-temperature performance when compared to SAE 15W-40 oil in ASTM D5293 cold cranking viscosity test. Advanced synthetic technology provides excellent viscosity control and outstanding extreme-temperature performance while minimizing oil consumption. The result: protection that’s boosted to the max.