Dear Doctor: I own a 2003 Pontiac Grand Am with only 20,000 miles. I have 7-year-old Marvel Mystery Oil that is opened. Is it still usable? I also have a gallon of the oil that is also around 7-years-old, but has never been opened. Is it useable? If either or both are usable, can I put it in the fuel tank of this car when I fill up? Carlo
Dear Carlo: Marvel Mystery Oil should still be as good as the day it was made, unless moisture got into it. You only need to add a small amount — 4 ounces per tank full at the most. I use Marvel in all my gas engines around the yard, including my small old 2 stroke outboard engine in addition to the 2-stroke oil mix. — Junior Damato, Motor Matters