Drivers are wasting their money on premium gas

For years, drivers have been under the impression that premium gas was better for their car. Not so, says AAA.

A new AAA study says American drivers wasted more than $2.1 billion dollars in the last year by using pricier premium-grade gasoline in cars built to run on more traditional regular fuel.

For cars designed to run on regular fuel, AAA found that using premium provided "no benefit" compared to regular gas -- no improvements to engine life, fuel economy or even reducing tailpipe emissions.

“Drivers see the ‘premium’ name at the pump and may assume the fuel is better for their vehicle,” said John Nielsen, AAA’s managing director of Automotive Engineering and Repair in a statement. “Premium gasoline is higher octane, not higher quality.”

As part of the study, AAA pumped regular and premium gas into cars with four-, six- and eight-cylinder engines designed to operate on regular-grade fuel. It then ran the vehicles, specifically a Toyota Tundra pickup and Dodge Charger and a Mazda3sedans, on a dynamometer, a sort of "treadmill for cars," to measure horsepower, fuel economy and tailpipe emissions to see how they would fare with both types of fuel.

Cars with engines designed for regular fuel make up 70% of the vehicles U.S. drivers use, with every car on Cars.com's list of the top 10 vehicles sold in August running on regular gas. That said, nearly 16.5 million U.S. drivers unnecessarily used premium-grade gasoline in their vehicle at least once in the last 12 months, according the driver advocacy organization. Those who chose the pricier gasoline did so at least once per month, on average.

Over the same time period the study found drivers needlessly used premium gasoline in their cars more than 270 million times.

Using premium gasoline in a car that doesn't need it is like "putting dollars out the tailpipe," Greg Brannon, AAA's director of Automotive Engineering, tells USA TODAY. But not all premium is bad.

"There's a good portion of vehicles that actually require premium fuel based on their engine design," says Brannon, noting those with turbocharged or supercharged engines need the higher grade fuel and drivers can actually "do engine damage by not running it."

Those with cars whose manufacturers recommend premium gas should continue use the higher-octane fuel, the study notes, as it did not test the effects of regular fuel on premium-designed engines.

Brannon has a simple tip for those looking to make the most out of their gas mileage. "Open that owner's manual, the most informative and most unread piece of documentation relevant to your car," says Brannon. "Understand what type of fuel that your vehicle requires and follow those recommendations."

Those looking to take things a step further should look gas that follows the industry's "Top Tier" standard established by automakers and gas retailers. In AAA's testing it found fuel that follows that standard can result in "19 times fewer engine deposits, increase vehicle performance and improve fuel economy."

"On average Top Tier gasoline is only pennies more, about 3 cents more, per gallon across the U.S.," says Brannon, than non-Top Tier fuel. "For pennies a gallon more you can do something really beneficial for your vehicle."

Follow Eli Blumenthal on Twitter @eliblumenthal