Like the five-day work week and glasses in about an hour, the 3,000-mile oil change is part of the American consciousness. Whether you follow the guideline or not, the number remains the same, decade after decade and car after car. It's been around so long, most of us don't even question its veracity. But where does the recommendation come from, and is it legitimate? If you check your car's user manual, you'll probably find you've been changing your oil more often than you need to, at least according to the people who designed your car. Most carmakers abandoned the 3,000-mile (4,828-kilometer) interval long ago, opting instead to advise...