15W-40 DIESEL MOTOR OIL THE ULTIMATE IN DIESEL ENGINE PROTECTION & PERFORMANCE ProOne’s 15W40 Heavy Duty Diesel motor oil is a blend of a high performance base oil and XPL+ Technology that dramatically lowers friction and protects against wear. This combination provides the best lubrication protection & performance in low-emission, high mileage, and modern heavy-duty diesel engines. Its robust anti-oxidant additive pack provides excellent thermal and oxidative stability that helps maintain high TBN’s which extends oil life and service intervals.