"As vehicles age, they change and some of these changes can result in costly repairs or replacement. Catalytic converter failure is one of the most common – and costliest -- problems faced by higher mileage vehicles. The phosphorus in all motor oil anti-wear packages is also an industry recognized catalyst poison.
Castrol GTX High Mileage is specially formulated with less phosphorus than other leading oils, replacing it with advanced technology invented and patented by Castrol that helps prevent catalytic converter and emission system failure and delivers unsurpassed protection against sludge, wear and oil burn-off*
*vs leading conventional oils, 5W-20 tested"