What Are Flex-Fuel Cars and What Types of Fuel Can They Use?

This once-common alternative fuel has almost disappeared from the market.


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Once a common part of the new-car market, flex-fuel vehicles recently shrunk to just a handful of new models. Designed to take advantage of ethanol-based gasoline, flex-fuel automobiles served as a unique subset of the alternative-energy landscape before government subsidies left them behind in favor of electric vehicles and plug-in hybrids.

Let’s take a look at flex-fuel cars and what types of fuel they are designed to use.

What Is Flex Fuel?

Flex fuel is a term that refers to an automotive drivetrain that can run on either traditional or ethanol-blended gasoline. Flex indicates the ability to use either fuel. The most common form of ethanol-based gas is called E85. During the summer months, E85 contains up to 83 percent ethanol content, while in the winter this amount is reduced in some regions to reduce problems with cold-weather starting.

E85 was created for two reasons. The first was to take advantage of the United States’ ability to produce bio-based ethanol, typically from corn. This had the dual effect of propping up domestic agriculture via subsidies and an attempt to reduce reliance on imported oil. It was also viewed as a renewable resource and therefore more environmentally friendly than the typical 90/10 percent gasoline/ethanol mix found at most pumps. This assertion is not universally accepted.

The drawbacks to using E85 include reduced fuel efficiency. The EPA states that flex-fuel vehicles return mileage that is between 15 and 27 percent worse than a regular gas-fueled engine because of the lower energy content in the fuel. This is offset somewhat by the typically cheaper price at the pump for E85.

What Makes Flex-Fuel Vehicles Different?

Although modern automobiles can tolerate a certain amount of ethanol in gasoline without serious issues, increasing ethanol content to 83 percent requires that the fuel system is made of materials that can resist its corrosive effects, especially in terms of the additional moisture in E85 fuel.

Flex-fuel vehicles use a sensor to detect the type of fuel being fed to the engine and adjust the combustion process accordingly. You can even mix a tank of standard gas with E85 with no risk of damage, although there’s no benefit to doing so.

Which Vehicles Can Use Flex Fuel?

Currently, the only new vehicles compatible with flex fuel are full-size pickups and cargo vans by Ford and General Motors. In the past, flex fuel was more common and available across a wider range of automobiles. Look for the “flex fuel” badge on the body, a yellow ring around the filler, or a yellow filler cap. The owner’s manual will also confirm if you’re driving a vehicle that can use E85 fuel.

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Benjamin Hunting
Benjamin Hunting is a writer and podcast host who contributes to a number of newspapers, automotive magazines, and online publications. More than a decade into his career, he enjoys keeping the shiny side up during track days and always has one too many classic vehicle projects partially disassembled in his garage at any given time. Remember, if it's not leaking, it's probably empty.