You've just done a fresh oil change on your car, and now you have a nice pan of the stuff. What exactly happens to motor oil, and what should you do with yours?

John Paul, AAA Northeast's Car Doctor, answers a question from a reader curious about using Marvel Mystery Oil.

But as engines have grown more efficient and oil formulas have improved, that rule of thumb is no longer a hard-and-fast requirement. So how often should you actually be changing your car's oil?

Everyone has an opinion on how often you should change your vehicle's oil, but what is the correct answer? Here is what you need to know to avoid engine damage.