How often should you change your oil? If you lived in the era of the shade tree mechanic or run a garage, your answer is probably "faithfully every 3,000 miles".
That answer may have been correct in the era of carburetors and bias-ply tires, but not today. Oil, like the cars that use it, has changed over the last thirty to forty years. Now you can go 5,000, 10,000, even 15,000 miles between oil changes. And if you use synthetic oil, that interval is even longer.
Some cars like most late model BMW, Honda and GM cars equipped with OnStar have onboard diagnostic tools to measure remaining oil life. All cars have the recommended service intervals published in their owner's manuals. And all manufacturers now recommend changing the oil between 5,000 and 10,000 miles depending on your driving conditions.
In my opinion, the only time you need to change the oil earlier than 5,000 miles is if you bought a brand new car and want to change the oil after the car's break in period. After that, just follow your owner's manual. Doing so will prevent you from voiding your warranty and save you money.