Is Ethanol Bad for Your Car?

Do you want to know the truth? We have more corn than we know what to do with -- and corn is cheap. It's taken the place of cane sugar in most of our prepared and packaged foods. Not only that, but it's increasingly sneaking into our gasoline, too, in the form of ethanol.

Conventional wisdom tells us that an inexpensive, domestically produced substitute for fuel would be a good thing; unfortunately, it's not that simple. With few exceptions, ethanol is not an acceptable fuel on its own merits. To some extent, however, ethanol does succeed at diluting our petroleum-based gasoline to help stretch our supply, offering ethanol blends.

It's also worth noting that ethanol in regular gasoline promotes the complete combustion of fuel within the engine. By oxygenating the gas during combustion, ethanol helps ensure fuel is fully burned, thereby reducing air pollution.

When the United States first embarked on this strategy, only a small percentage of ethanol was added to the mix -- generally, most engines didn't even notice and kept running as usual. But now, gasoline is most commonly produced with 10 or 15 percent ethanol (known as E10 and E15, respectively) and some politicians want to push that to as high as 20 percent.

We should also note that there's an ethanol-gas blend known as E85 -- which is a combination of ethanol and gasoline that consists of 51 to 83 percent ethanol blended with gasoline. This type of fuel is only acceptable for use in specially engineered vehicles marketed with a "Flex Fuel" designation. Flexible fuel vehicles have access to over 4000 E85 gas stations across 42 states.

The short answer is ethanol fuel can potentially be harmful to your car’s fuel system, especially in older vehicles. Ethanol absorbs moisture from the air, which can lead to corrosion in fuel lines, injectors, and other components.

Additionally, ethanol's solvent properties may degrade rubber and plastic parts in the fuel system. While modern cars are generally designed to handle ethanol blends, understanding its effects can help maintain your vehicle’s performance and longevity.

How much of a difference can there be between E10 fuel, which is in widespread use (although not warmly embraced) and E15 fuel (also known as unleaded 88 octane gas)? How much damage can be caused by that extra 5 percent?

The evidence is compelling enough that in 2011, several automakers said that owners of older cars running E15 were in danger of voiding their warranties. Although it must be said that most cars older than the Environmental Protection Agency's 2001 model year cutoff were unlikely to still have valid, unexpired warranties, anyway.

We're used to E10, after all -- and presumably, our cars are, too. But when the EPA designates a fuel blend as "legal," they're really enabling themselves to saturate the market with this diluted gasoline, since the agency can ultimately control what's available to consumers. If E15 is cheaper to supply than E10, drivers will gradually be forced to buy it. It's that, or don't fill up at all.

Mike Allen of Popular Mechanics says that under ideal conditions, a gasoline-ethanol blend is perfectly acceptable. But consumers cannot control those conditions, and they have no way of knowing if the fuel they're buying has been contaminated. All gasoline is susceptible to changes due to weather and moisture content, but ethanol exacerbates this problem.

A higher concentration of alcohol in a gas tank (any gas tank -- at the production facilities, the tankers traveling on the highway, the storage tanks at a gas station, your car's reservoir and even the red plastic can sitting on the floor in your garage) means that the alcohol can grab and hold more water than straight gasoline.

Ethanol's hygroscopic nature means it can absorb water from the environment, leading to phase separation where the water and ethanol mixture separates from the gasoline. This can happen at any stage of transport, storage, or usage and can create a layer of water and ethanol that is not usable by your car's engine, potentially causing performance issues or damage.

Even if the fuel’s environmental conditions aren't seriously compromised and the ethanol stays in suspension, ethanol can still cause damage, especially in older vehicles. Many older fuel system components were not designed to resist alcohol’s corrosive properties.

As ethanol travels through the system, it can degrade rubber, plastic, and certain metals. While modern vehicles are generally built to handle ethanol blends, the solvent properties of ethanol can loosen deposits within the fuel system. These deposits do not dissolve and can be carried along until they cause blockages elsewhere.

Most vehicles manufactured in recent years are designed to handle ethanol blends up to E15 without significant issues. However, owners of older vehicles should be cautious and consider using fuel additives or avoiding high-ethanol blends to mitigate potential risks.

A 2012 study by Auto Alliance showed that some cars (model years 2001 to 2009) showed internal engine damage as the result of using an ethanol fuel blend. Damage to the valves and valve seats was evident in some of the cars tested.

One of the 16 cars in the Auto Alliance study failed emissions compliance standards, which means it emitted more pollution than allowed by the EPA. The study also showed that cars running on E15 take a hit on gas mileage -- so they require more fuel to travel the same distance, which counteracts the benefits of diluting it in the first place.

Recent studies indicate mixed results regarding E15’s impact on fuel efficiency and engine health. While modern vehicles are generally compatible with E15, older models may still face risks. Public awareness of E15 has grown, and infrastructure improvements have made it more accessible, but concerns about ethanol's long-term effects persist. Regular updates from industry experts and regulatory bodies are essential to keep consumers informed about the safest and most efficient fuel options for their vehicles.

Some organizations initially sought to delay the widespread adoption of E15 until the public understood its implications. Today, the EPA requires clear labeling on gas pumps to communicate the ethanol content and assure users that E15 is safe for most modern vehicles.

While infrastructure for E15 distribution has improved significantly, public awareness has also increased. According to recent surveys, more drivers are now aware of E15 and its potential effects on their vehicles. However, there is still a need for ongoing education, as some misconceptions persist. The agricultural industry continues to advocate for higher ethanol blends, emphasizing the importance of understanding both the benefits and potential risks associated with E15.

We updated this article in conjunction with AI technology, then made sure it was fact-checked and edited by a HowStuffWorks editor.