Viewer-submitted questions for The Car Doctor: Q: I perform routine maintenance on my family’s cars and just want to know your thoughts on Marvel Mystery Oil as both a fuel additive and oil additive.

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

Walk into any parts store and you'll see the rows of glossy bottles promising to stop engine wear, boost fuel economy, and make your old clunker run like it just rolled out of the factory. The auto ...