Let the driver beware: Not all gasoline is created equal. As the summer-vacation driving season begins, paying attention at the pump can add miles per gallon to your fuel economy, and protect your engine.
Differences in octane level and the amount of ethanol added to gasoline can have a dramatic impact on fuel economy and emissions. In a worst-case scenario, using bad gas could even void the manufacturer's warranty.
The key risks: Lower-than-expected octane and higher mixes of ethanol.
Low-octane fuel — rated 85 or 86, as opposed to 87 for regular gasoline — is common in the Rocky Mountain states, says General Motors fuel specialist Bill Studzinski. The practice goes back to the days of carbureted engines, when lower octane helped vehicles run smoothly at altitude. The electronic engine controls that have replaced carburetors make the lower octane unnecessary and potentially harmful.
"I felt like a fool," says Rodney Gutzler of Sioux Falls, S.D., former owner of a 2012 Scion iQ. "Here I was in a little bitty car that was supposed to get 36 mpg in the city, and I was getting 25."
The 85-octane gas spread from the mountains of western South Dakota into the eastern plains last year, says David Montgomery, a reporter for the Sioux Falls Argus Leader. The state Legislature has since passed a law restricting sales to the west and requiring a warning label on pumps: "This octane level may not meet minimum manufacturer specifications. Consult your owner's manual before fueling."
Automakers would prefer a total ban on 85- and 86-octane gasoline. Less than 2 percent of the vehicles in the U.S. have carburetors, according to GM. The other 98 percent have computer controls that adjust for altitude and require the manufacturer's specified gasoline to meet emissions, fuel economy and performance standards.
"We do not endorse the use of 85 octane or lower," Studzinski says.
A lawsuit pending in South Dakota seeks damages for drivers who were "knowingly and fraudulently charged inflated prices" for 85-octane gas, which costs less at the pump than 87, Montgomery says.
"My Scion iQ clearly stated that no gasoline lower than 87 octane should be used because it could damage the engine," Gutzler says. "The pumps where I got 85 octane weren't labeled. Who knew what we were buying?"
The other potential problem is less geographically widespread. But unlike 85-octane gas, which seems to be waning, higher ethanol mixtures are likely to become more common to reduce greenhouse-gas emissions and boost use of renewable fuels.
Virtually all gasoline sold in the U.S. has 10 percent ethanol. Vehicles are engineered to run easily on it. But a new 15 percent blend, called E15, could be problematic. Only a handful of service stations sell E15 now.
The U.S. Environmental Protection Agency says E15 works fine with the emissions systems of vehicles dating to the 2001 model year, but automakers didn't certify other systems for it that long ago. GM, for instance, approves E15 only for 2012 and later model years. The mixed signals from the EPA and automakers' recommendations create room for user error.
"A recent AAA survey finds a strong likelihood of customer confusion, and the potential for voided warranties due to E15," says Nancy Cain, spokesperson for the AAA Michigan motor club. "We want more education so customers know what they're buying and what their vehicles need."