Cheaper E15 Ethanol Fuel Is Here To Stay, But Maybe You Shouldn’t Put It In Your Car

Ethanol’s an interesting fuel. Blended with gasoline, it can offer big octane and serious knock resistance, but it can also wreak havoc on incompatible fuel systems. While a 10 percent blend has been fairly normal at the pumps for decades now, E15 looks like it’s sticking around, and while it might be tempting to save a little bit on fuel, there are some reasons why it isn’t ubiquitous yet.

This cheaper blend with an extra slug of distilled corn juice has already been around for a while, but it’s historically been isolated to use in cold seasons, when smog is less of an issue. Over the past few years, a number of emergency orders have extended the sale of E15 through the summer months, and it looks like that’s continuing for 2025. However, just because it’s available doesn’t mean you should just put it in your car.

The EPA claims that cars made after 2001 will happily accommodate E15, but that’s not exactly accurate. While E85-capable vehicles can safely handle E15 since 15 percent ethanol by volume is far less than 85 percent ethanol by volume, there are lots of vehicles made after 2001 that aren’t designed for E15. For instance, BMWs only approves a maximum of 10 percent ethanol content in its vehicles, as does Mazda, as does Mercedes-Benz on all models not approved for E85. Volvo only approves a maximum of 10 percent ethanol content across its lineup, as does Mitsubishi.

Some other manufacturers like Nissan are more selective when it comes to E15 approval. The current Frontier, Rogue, Z, Pathfinder, and Altima can take E15, but the Sentra, Kicks, and almost all outgoing models like the previous-generation Armada aren’t rated to handle it.

So what happens if you run a car not rated for E15 on this particular blend of gasoline? Well, ethanol is hygroscopic, meaning it pulls in moisture. If not kept tightly sealed, the ethanol in blended gasoline can attract water and separate from the gasoline, potentially leading to fuel system damage. Thankfully, modern fuel systems are generally sealed pretty well, but water contamination isn’t the only way higher ethanol concentrations can affect fuel systems.

For instance, ethanol and oxygen can form acetic acid, the active ingredient in vinegar. Anyone who’s let old parts sit in a vinegar bath overnight will tell you it does a modest job of removing light rust and tarnishing, but similar acidity could also affect the integrity of fuel system components over the long run. It’s also worth noting that rubber fuel system components are rated for a certain level of ethanol, and lines and seals compatible with E10 might not be compatible with E15, leading to premature degradation.

Another thing to note about E15 is energy density. According to the Department of Energy, pure ethanol is roughly 30 percent less energy-dense than gasoline, so going up from E10 to E15 will likely result in a marginal decline in fuel economy. It will likely only be a few percentage points, but if the price of E15 in your area is only a touch cheaper than E10, you might not actually save any money.

Yes, E15 will likely be cheaper than more common blends of up to 10 percent ethanol, but it’s a good idea to check your owner’s manual to see if your car can run it before selecting it at the fuel pump. One mistaken tank probably won’t do any damage, but prolonged use in a fuel system not designed for it could result in unexpected wear. Also, reduced energy density means E15 might not work out cheaper on a cost-per-mile basis.

Top graphic images: stock.adobe.com; Nissan

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