Many Iowans follow the rule of keeping their vehicles’ gas tanks at least half full during extremely cold weather as it can help engine performance, but be sure to choose the pump carefully.

A new report finds paying for premium gas may not be worth the extra price. Gail Weinholzer, at AAA-Iowa, says the motor club study found some people will pump premium fuels occasionally as a “treat” for their engines.

Weinholzer says, “Many people do use it in that way but looking at the return on investment, only a 2.7% increase in fuel economy and a 1.4% increase in horsepower certainly doesn’t justify the 20-to-25% higher cost of putting premium into your car versus regular.” While regular gas is averaging two-36 a gallon in Iowa, premium blends are averaging two-73. The report finds only 16-percent of the vehicles on the road are required by the manufacturer to use the pricey premium fuel of 91 octane or higher.

“If it’s required, use it, but if it’s recommended, it’s really not the best idea,” she says, “and it certainly doesn’t provide the ROI.” On the other side of the coin, some Iowans may see certain ethanol blends being advertised in the $1.85, a good 50-cents a gallon cheaper than regular gasoline. Weinholzer reminds, those less expensive blends are cheaper for a reason.

“Not to dissuade people from using ethanol, whether it’s E10 or E15, but it costs less because there’s less fuel economy associated with it,” Weinholzer says. “When it comes to fuels and your vehicle, the best way to maintain your warranty is to put in whatever fuel the owner’s manual requires, not recommends, but requires.” An earlier report from the motor club found drivers nationwide waste more than $2 billion per year fueling vehicles with higher-octane gasoline. It concluded there is no benefit to using premium gasoline in cars designed to run on regular.