The synthetic oil should be changed every year or every 10,000 to 15,000 miles, depending on the oil filter. It should be changed when it is worn out or aged. The oil degrades under heat and pressure, and builds up harmful particles that must be removed. In addition, the oil breaks down over time, even when the car is parked for an extended period of time.
Each rod has some way of indicating the appropriate oil level, whether it's two holes, the letters L and H (low and high), the words MIN and MAX, or simply a scratched area. On many newer models, the weight of the car's engine oil is printed on the cap where the oil is added and appears in the maintenance section of the owner's manual.
