Chances are you've seen "contains up to 10% ethanol" printed somewhere on a gas pump and wondered what that actually means. Is it bad for your car? Does it help or hurt the environment? To answer that, it helps to know how ethanol ended up in your tank in the first place.
Back in 1990, Congress passed major amendments to the Clean Air Act aimed at reducing vehicle related air pollution. Among other things, the law created programs that required cleaner burning gasoline in certain parts of the country with serious smog problems. To meet those standards, refiners began adding oxygenates, compounds that contain oxygen and help reduce emissions of carbon monoxide and some other pollutants.
Why MTBE disappeared
For years, the most common oxygenate was MTBE, or methyl tert butyl ether. But during the 1990s, MTBE started turning up in drinking water supplies after leaking underground storage tanks and fuel spills contaminated groundwater. Although the health risks were debated, the contamination was enough for many states to phase out or ban MTBE, prompting refiners to look for another option.
Ethanol became the replacement. It's an alcohol made from plants, primarily corn in the United States, and it offered many of the same air quality benefits without the same groundwater contamination concerns. Today, the vast majority of gasoline sold in the U.S. contains about 10% ethanol, commonly known as E10, although ethanol free gasoline is still available in some areas.
So is that a problem? Depends who you ask. There are two camps here and both have reasonable arguments.
The case for ethanol
The first camp says there's little reason to worry. Most modern gasoline powered vehicles are designed to run on E10 without any issues. Electronic fuel injection and onboard computers automatically adjust the engine's air fuel mixture, so drivers generally won't notice any difference.
Many older fuel injected vehicles also handle E10 just fine. Vehicles built decades ago, especially classic cars or those with older fuel system components, may experience problems over time because ethanol can be harder on certain rubber hoses, seals and gaskets that weren't designed with alcohol blended fuels in mind.
Supporters also point to the environmental benefits. Because ethanol contains oxygen, it can help reduce emissions of carbon monoxide and certain hydrocarbons, particularly in older engine designs. And since most U.S. ethanol is made from crops rather than petroleum, supporters argue it can also reduce reliance on fossil fuels, although its overall environmental impact remains the subject of ongoing debate.
The case against it
Critics aren't so convinced. Their concerns usually center on using ethanol blends that exceed what a vehicle was designed to handle. While many newer vehicles are approved to use E15, which contains 15% ethanol, and flex fuel vehicles can safely run on E85, using higher ethanol blends in incompatible vehicles can lead to corrosion, deterioration of fuel system components and other mechanical problems over time.
Fuel economy is another common criticism. Ethanol contains less energy per gallon than gasoline, so blending it into fuel slightly reduces gas mileage. With E10, the difference is usually around 2 to 3%, but it can become more noticeable with higher ethanol blends.
Some critics also question ethanol's environmental benefits, arguing that the energy required to grow, harvest and process corn offsets some of the emissions reductions achieved at the tailpipe. Others raise concerns about the agricultural impacts of large scale corn production, including fertilizer use, water consumption and land use.
So what should you take away from this?
Neither side is making things up. For most drivers, E10 is a perfectly suitable fuel that modern vehicles are specifically designed to use. At the same time, ethanol can create problems for certain older vehicles or when higher ethanol blends are used in engines that weren't designed for them.
If you own a car built in the last couple of decades, E10 is almost certainly nothing to worry about. If you're driving a classic car, a small engine, a boat or you're considering E15 or E85, it's worth checking your owner's manual to see which fuels your vehicle is approved to use.
Either way, now you'll know the story behind that little ethanol label the next time you stop at the pump.
