Product DescriptionAs 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-30 tested.Amazon.comMotor oil is made from crude oil and is used to lubricate, clean, and cool engines. Types of motor oil include conventional, synthetic, diesel, bio-based, hybrid (blends of conventional and synthetic), and recycled oils. Motor oil varies in weight and viscosity, as well as additives that some manufacturers add to the oil during the refining process. A numerical code system created by the Society of Automotive Engineers (SAE) grades motor oils according to viscosity--the higher the number between 0 and 60, the more viscous (thicker) the oil is. Most consumer motor oils are graded by two numbers, with the first number indicating cold weather (Winter or "W") performance.SAE 10W-40This oil has a weight of SAE 10W-40, meaning it has an SAE viscosity rating of 10 in cold temperatures and a rating of 40 at normal operating temperature. Always check your vehicle's owner's manual to verify that this is the correct weight of motor oil for your vehicle.Conventional Motor OilThis oil is a conventional motor oil, meaning it is refined from crude oil or petroleum products. Conventional motor oils may or may not have additives included after refining. Conventional motor oils are more versatile than synthetic or hybrid motor oils, because they are suitable for use with nearly all types of modern vehicle engines, from cars and trucks to motorcycles, ATVs, farm equipment, and more.High Mileage OilThis oil is primarily designed for use in high-mileage cars and trucks, including both older vehicles and new vehicles that see heavy long-distance use. Extra additives are included to minimize compression loss, and to condition rubber seals and gaskets to prevent fluid leakage in older or high-mileage vehicles.