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Running your vehicle on a mixture of different fuels, such as gasoline and diesel, can cause many problems. Fortunately, there isn’t much to worry about if you accidentally put ethanol gas into your gasoline car when there’s still non-ethanol gas in its tank.

Most modern gasoline engines can burn gas blends that contain up to 15% ethanol without problems. If you drive a flex-fuel vehicle, it can handle up to 83% ethanol-blended gas. And given the benefits of ethanol gas, you might even get more mileage compared to running on non-ethanol-blended gas.

While your car can handle the occasional mistake, avoid mixing ethanol and non-ethanol gas. Stick to the manufacturer-recommended fuel blend that the engine can burn.

gas station displaying fuel prices
Most modern gasoline engines can burn gas blends that contain up to 15% ethanol, so there’s no need to worry much if you accidentally mixed ethanol and non-ethanol gas in your car.

What Is Ethanol Gas?

Ethanol-blended gas is gasoline with the addition of ethanol. Also called ethyl alcohol or grain alcohol, ethanol is responsible for the intoxicating effect of alcoholic beverages.

Ethanol is a renewable biofuel made from biomass, such as corn grain. It can be used as a fuel by itself, but often serves as an additive for gasoline.

Compared to gasoline, ethanol stores less energy. You’ll need to consume more ethanol to match the energy output produced by burning gasoline.

However, ethanol has a higher octane number than gasoline. It requires higher pressures before it can combust, so it’s less likely to vaporize or burn outside the pressurized confines of the engine’s cylinders.

Why Is Ethanol Mixed With Gas?

Ethanol-blended gas improves the stability of pure gasoline by increasing its octane number. The lowest octane rating for fuel is 87, and non-ethanol gas has difficulty achieving this rating. Adding ethanol raises the octane rating of the resulting fuel blend. It also prevents knocking, the uneven combustion of gasoline that makes a distinctly loud sound and can damage the engine.

Furthermore, ethanol improves the oxygen content of gasoline. More oxygen increases the engine’s efficiency at burning the air-fuel mixture. Ethanol also lowers your vehicle’s emissions by reducing unburned and incompletely burned gas.

There are several ethanol gas blends available. E10 is the most common blend and has an ethanol content of 10%. If you accidentally put ethanol-blended gas in your car, it’s likely E10, which minimizes risk to your engine.

e10 nozzle on a fuel tank
E10 is the most common blend and has an ethanol content of 10%, and only poses minimal risk to your engine.

Another available blend is E15, which has an ethanol content ranging from 10.5% to 15%. It’s compatible with light-duty vehicles made in 2001 and above. Newer flexible fuel vehicles (FFVs) can also burn E15 fuel.

Then there’s the E85 ethanol gas blend. Also called flexible fuel or flex fuel, it can contain up to 83% ethanol. Most gas cars can’t run properly on E85 because it generates less energy than lighter ethanol-blended fuels. FFVs are the only ones that can safely use this type of fuel.

Any information provided on this Website is for informational purposes only and is not intended to replace consultation with a professional mechanic. The accuracy and timeliness of the information may change from the time of publication.

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