I go by the mileage and the time. 3500 miles is perfect. If one sits for a extended period, fresh oil is one thing it gets before going on the road again. I use Dino 20/50 Castrol in the Scoots. GM oil in the G6 and have used several different ones in the Ranger. Just cain't see a year on anything that gets used. Cain't believe I started a OIL Thread!! But a oil with a recommended 1 year between changes???