When should I change my oil? We recommend changing the oil every 3,000 miles if you are using a synthetic blended oil. We recommend changing your oil every 7,500 miles if you are using a full synthetic oil. The oil change is very important. As oil becomes old, the anti-friction qualities decrease. This can lead to internal engine wear and an engine sludge build up. A good working oil also helps in keeping excessive engine temperatures to a minimum.