The rigors of extreme duty cycles and high idle time as well as harsh environments experienced in mining, construction and agriculture can be very demanding on the motor oil of heavy-duty diesel engines. Valvoline All-Terrain SAE 15W-40 Heavy Duty Diesel Engine Oil is uniquely designed and tested to protect hardworking heavy-duty diesel engines operating in severe duty cycles (including high idle time), both off and on the highway applications. Our formulation provides outstanding wear protection under extreme load regimes and temperatures. Plus, enhanced viscosity and oxidation stability help fight deposits and sludge for increased performance and longevity.