No matter how good your oil, its additives eventually become depleted, and the contaminant level becomes too high for the oil to function as it should. So, in addition to keeping an eye on the oil level in your engine, you should plan regular oil and oil-filter changes to keep your engine in top condition.

Your driving habits dictate how often you should change your oil to maintain peak performance and prolong the life of your engine. Eighty percent of our driving qualifies as "severe service"- and demands more frequent oil changes than "normal service."

Although improvements in engines and oils - and the use of unleaded gasoline - have extended normal-service oil change intervals to as long as 7,500 miles for some vehicles, the recommended interval for severe service is three months or 3,000 miles, whichever comes first. For most drivers, the time limit will come before the mileage limit. Your owner's manual specifies the correct oil change intervals to maintain your warranty-under both normal- and severe-service conditions.