Are you among the millions of Americans who like to “treat” their cars to an occasional tankful of premium gasoline? If so, you’re not only not doing anything good for your car -- you’re also contributing to a waste of some $2.1 billion every year.

When the Federal Reserve hiked interest rates this month for the first time in nearly a decade, Fed Chair Janet Yellen said the takeaway for the average American is the U.S. economy is improving.