Lucas 15W-40 Magnum High TBN CI-4 Oil is a blend of high quality base oils and an additive package that allows extended drain intervals and a much higher degree of protection from metal to metal contact. The exclusive additive package in Lucas 15W-40 insures a protective film on parts at all times. Also, the additive package is more resistant to break down from the solvents in diesel fuel than common additive packages found in regular 15W-40 blends. Motor oil is usually changed because it's contaminated with combustion by-products, not because it's worn out. The high detergent action of Lucas 15W-40 allows up to twice as much contamination to be held in suspension and still have good lubrication qualities.