Changing your oil is the least expensive way you can extend the life of your vehicle. Oil changes are important! However, they are based on mileage rather than time, as the oil breaks down with usage. If you are concerned about how much time has passed since your last oil change, check your oil. It may be dark, but should look clear. If it looks black, change it!!!! If in doubt, change the oil. It won't hurt a thing. If your vehicle burns oil, be sure to check frequently and keep it in the full zone on the dip stick.