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The Ethanol Myth
Consumer Reports' E85 tests show that you’ll get cleaner emissions but poorer fuel economy—that is if you can find E85.

The Bush administration has been pushing ethanol as a renewable, homegrown alternative to gasoline. Now, the auto industry is abuzz with the promise of its flexible-fuel vehicles (FFVs), which are designed to run on either gasoline or the blend of 85 percent ethanol and 15 percent gasoline called E85.

GM's advertising says, "Energy independence? The answer may be growing in our own backyard," and has coined the slogan "Live green, go yellow," referring to the corn from which most U.S. ethanol is made. DaimlerChrysler, Ford, and GM have said that they plan to double production of FFVs and other biofuel vehicles to 2 million by 2010.

A recent Harris Interactive study of vehicle owners found that more than half were interested in purchasing an FFV, mostly for reduced dependency on petroleum and improved fuel economy.

But after putting a 2007 Chevrolet Tahoe FFV through an array of fuel economy, acceleration, and emissions tests, and interviewing more than 50 experts on ethanol fuel, CR determined that E85 will cost consumers more money than gasoline and that there are concerns about whether the government's support of FFVs is really helping the U.S. achieve energy independence. Among our findings:

The fuel economy of the Tahoe dropped 27 percent when running on E85 compared with gasoline, from an already low 14 mpg overall to 10 mpg (rounded to the nearest mpg). This is the lowest fuel mileage we've gotten from any vehicle in recent years.

With the retail pump price of E85 averaging $2.91 per gallon in August, according to the Oil Price Information Service, which tracks petroleum and other fuel prices, a 27 percent fuel-economy penalty means drivers would have paid an average of $3.99 for the energy equivalent of a gallon of gasoline.

When we calculated the Tahoe's driving range, we found that it decreased to about 300 miles on a full tank of E85 compared with about 440 on gasoline. So you have to fill up more often with E85.

The majority of FFVs are large vehicles like the Tahoe that get relatively poor fuel economy even on gasoline. So they will cost you a lot at the pump, no matter which fuel you use.

Because E85 is primarily sold in the upper Midwest, most drivers in the country have no access to the fuel, even if they want it.

The FFV surge is being motivated by generous fuel-economy credits that auto-makers get for every FFV they build, even if it never runs on E85. This allows them to pump out more gas-guzzling large SUVs and pickups, which is resulting in the consumption of many times more gallons of gasoline than E85 now replaces.
We put the Tahoe through our full series of fuel-economy and acceleration tests while running on each fuel (see our test results). When running on E85 there was no significant change in acceleration. Fuel economy, however, dropped across the board. In highway driving, gas mileage decreased from 21 to 15 mpg; in city driving, it dropped from 9 to 7 mpg.

You could expect a similar decrease in gas mileage in any current FFV. That's because ethanol has a lower energy content than gasoline: 75,670 British thermal units per gallon instead of 115,400, according to the National Highway Traffic Safety Administration. So you have to burn more fuel to generate the same amount of energy. In addition, FFV engines are designed to run more efficiently on gasoline. E85 fuel economy could approach that of gasoline if manufacturers optimized engines for that fuel.

When we took our Tahoe to a state-certified emissions-test facility in Connecticut and had a standard emissions test performed, we found a significant decrease in smog-forming oxides of nitrogen when using E85. Ethanol, however, emits acetaldehyde, a probable carcinogen and something that standard emissions-testing equipment is not designed to measure. But that might be a relatively minor evil. "Acetaldehyde is bad," says James Cannon, president of Energy Futures, an alternative-transportation publication, "but not nearly as bad as some of the emissions from gasoline."


Visit our Guide to Stretching Your Fuel Dollars for gas-saving tips, a list of the most fuel-efficient cars, and a rundown of other alternative fuels.

Test results: E85 vs. gasoline

This chart shows how our 2007 Chevrolet Tahoe performed while running on E85 and gasoline in three fuel-economy tests and overall, in four acceleration tests, and in three emissions tests for gasoline vehicles.

Fuel economy, mpg
City 7 9
Highway 15 21
150-mile trip 13 18
Overall 10 14
0-30 mph, sec. 3.4 3.5
0-60 mph, sec. 8.9 9.1
45-65 mph, sec. 5.7 5.8
Quarter-mile, sec./mph 16.8/84.6 16.9/84.5
Emissions, parts per million
Nitrogen oxide 1 9
Hydrocarbons 1 1
Carbon monoxide 0 0

*Blended with 10 percent ethanol.