E85 Fuel Explained: What to Know about Ethanol-Blended Gasoline

April 04, 2025

Print This Article Share it With Friends

by David Gluckman (Car and Driver) Not all cars are compatible with this ethanol-rich fuel, and deciding whether to fill up with it requires some consideration.

...

Even if your car's engine isn't compatible with E85, it's a topic of increasing relevance in discussions of gasoline's environmental impact, shifting energy reliance from foreign oil, and this alternative fuel's potential to increase use of renewable energy.

...

E85 is a liquid fuel consisting of up to 85 percent ethanol with the rest straight gasoline. It's pitched as an alternative to pure gasoline and claims a variety of benefits, which we'll get into later. This blended fuel can use ethanol from different sources, such as fermented plant sugars (chiefly corn and sugarcane) or waste cellulose from wood processing or agriculture activities. Swapping in locally produced ethanol reduces dependence on foreign petroleum sources while also helping the farmers and industries that supply the ethanol.

...

Note that most gasoline sold in the U.S. has some amount of ethanol blended in, usually up to a max of 10 percent, denoted as E10. So potentially without realizing it, you're already putting some amount of ethanol into your vehicle's gas tank. The difference with E85 is that the portion of ethanol is greater—up to that 85 percent maximum. The actual amount of ethanol in a particular shipment of E85 depends on regional and seasonal factors, in part to ensure that a vehicle running the fuel will be able to start in cold temperatures.

How Does E85 Work in a Vehicle?

Ethanol-rich fuel such as E85 goes into the gas tank like any other gasoline blend. From there, it travels through the fuel system to the cylinders, where it gets burned (or combusted). The combustion process is more or less the same as it is when the vehicle is running on normal gasoline.

But, as we mentioned, not all vehicles are designed to accept fuel with increased amounts of ethanol mixed in. Those that have been are referred to as flexible-fuel vehicles, flex-fuel vehicles for short, or FFVs for shortest; they're also sometimes called dual-fuel vehicles. FFVs have sensors to detect the amount of ethanol present and calibrations to adjust for things like spark timing on the fly. FFVs' fuel systems use different materials to ensure that the higher levels of ethanol won't cause harm, as this alcohol can be corrosive to both plastics and metals.

...

Pros

Domestically produced ethanol makes the resulting E85 fuel and its users less dependent on foreign oil (and petroleum in general), giving it both geopolitical advantages and comparatively reduced transport costs.
Because corn, sugarcane, wood, and other sources of ethanol are renewable, the fuel can be less environmentally costly.
The sourcing and composition of the ethanol used in E85 fuel can lead to lower costs compared with standard gasoline blends.
...
Adding ethanol to a gasoline blend increases its octane rating, meaning it is more resistant to engine knock, or the premature detonation of fuel in the combustion chambers. This allows engine tuners to coax more power from vehicles with flex-fuel engines.
Cons
Because E85 has lower energy density than pure gasoline, fuel mileage suffers. This may or may not be offset by the cost savings of E85 compared with standard unleaded gas, but at the very least, it will reduce your vehicle's range.
E85 is not available at all stations, in all regions, or at all times of the year, so you may be able to grab a tank of it here and there but not switch over completely.
Higher concentrations of ethanol in a fuel make it more difficult to ignite at low temperatures, hence the adjustment of ethanol content and the fuel's availability in cold climates and during winter. This could cause problems for someone who fills up in a warmer location and then drives somewhere colder.
Ethanol will not grab water out of the air but will absorb the liquid if it is present, which can wreak havoc on a fuel system not designed to deal with it. Water can also be introduced to the fuel if it is not handled properly, such as being added to a storage tank that hasn't been thoroughly cleaned to remove so-called "water bottoms" and sludge that can accumulate over time.
Ethanol's tendency to dissolve things such as resins, rust, and other gunk that may already be in your gas tank means it may clog your engine's fuel filter more quickly. This is important to monitor, especially if you're transitioning from, say, E10 to E85.

Is E85 Right for You?

Before you decide to reach for that yellow handle, make sure the engine in your car is designed to work with it. If you're uncertain, consult your owner's manual or check for an FFV badge. There may be a label near the fuel filler or on the gas door, or a yellow gas cap or ring around a capless filler that tells you E85 is okay. Note that some models are sold with the same basic engine with and without the necessary changes to make them an FFV, so you can't assume that a vehicle is compatible with E85 based on the make, model, and year alone.

For those shopping for a new flex-fuel vehicle, the EPA and the Department of Energy's fueleconomy.gov site has a filter to show only E85-compatible options. New models offering E85-spec engines include vehicles popular in fleets, such as GM's full-size pickups and the Ford Explorer, as well as some small crossovers from Chevy and Buick. The used market is an option as well. READ MORE