Don't pay the extra 15 to 20 cents per gallon for a higher-octane fuel if your engine doesn't require it because some experts say it's a total waste of money.

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So what do you need to know?

Here's the good news: You don't have to know anything about the functioning of your engine to make sure you're putting fuel with the right octane rating in your tank. All you have to do is look into your trusty owners' manual and see what you should be doing. If your vehicle requires a high octane rating, the manual will tell you. Otherwise, don't pay the extra 15 to 20 cents per gallon for a higher octane fuel. "Putting high-octane fuel into a car that only needs low-octane fuel is a total waste of money," says Arman.

According to AAA's Nielsen, using a higher-octane fuel than your car requires won't hurt anything, but it also won't help -- and you'll be paying more for it, so it hurts in a different way. Then again, if your car is making knocking and pinging noises, it can be a good move to try a gas with a higher octane rating.

"Go up one grade of fuel and see if it solves the problem," says Arman. "It usually does." While occasional knocking and pinging is fairly normal and doesn't necessarily indicate any serious problem, persistent detonation-caused noise should not be ignored because it may lead to more serious engine damage.

Keep reading for more information on car engines and fuel economy.