As E15 Gas Becomes More Common, Remember That It's Terrible For These Engines

[mahatmakanejeeves]

I doubt that it's "illegal" to use E15 in old engines, but they weren't designed to run on it.

CULTURE • JALOPNIK EXPLAINS
As E15 Gas Becomes More Common, Remember That It's Terrible For These Engines

BY B. L. JOHNSON APRIL 12, 2026 5:25 AM EST

Way back in 1978, the Environmental Protection Agency (EPA) issued a waiver to the Clean Air Act, allowing gasoline that was made up of up to 10% ethanol, or E10, to be sold at the fuel pump. E10 is still the gas that is most commonly sold today. 

Decades later, in 2010, the EPA would begin allowing E15 gas (15% ethanol) to be used, but only in 2007 model year cars or newer. The final rule would allow E15 to be used in 2001 cars and newer, as well as modern flex-fuel engines. E15 is normally not available in the summer, but the EPA has issued waivers in the past few years to allow its sale year-round. (Here's why ethanol is mixed into gasoline in the first place.)

It is illegal to use E15, sold as 88 octane, in older engines. It is also illegal to use it in lawnmowers, motorcycles, boats, heavy-duty vehicles like delivery trucks, and aircraft. Why? Ethanol is not kind to engines, especially older ones, and that 15% amounts to a lot of corn juice blended into your gasoline. If an engine isn't built to deal with ethanol, it can do a lot of damage. But regardless of how old your car is, you should check to see if your manufacturer has even authorized E15 gas to be used in it. Most manufacturers have only authorized its use in cars much newer than 2001, and some don't allow it at all.

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