Governors' Biofuels Coalition

The auto and oil industries plan to release a report on Wednesday indicating that some cars running on E15, the 15 percent ethanol blend that was recently authorized by the Environmental Protection Agency, experienced engine damage.

But officials at the Energy Department counter that the study is flawed and that the department’s own research, which the E.P.A. relied on in approving E15, demonstrates that cars now running on the standard blend, called E10, will do just fine on E15.

The report is now online.

The dispute is emerging because of an unanticipated twist in the fuel market, with Congress having mandated the use of more ethanol, which the makers are having trouble selling.

As the market for gasoline has declined, gasoline in many parts of the country is now a mixture of 10 percent ethanol, known as E10, the maximum that was allowed until January. That is the level the automakers say their vehicles can use without damage. (Ethanol producers refer to this limit as the “blend wall.”)

Arguments between the oil and auto industries over which should have to make adjustments to meet clean air goals have been common for decades. But some industry experts describe the current conflict between the auto companies and the government as unparalleled.

It is reflected in inch-high letters embossed on the filler-pipe caps of new Toyotas, a label on which “E15” is shown in a red circle with a slash through it reminiscent of a no-smoking sign.

For years, Ford vehicles have come with a cap that warns against use of E20 gasoline because a few years ago, Minnesota was considering authorizing its use. Ford is now considering changing that warning to refer to E15 as well. General Motors, Chrysler and nearly all of the other automakers also warn that using E15 may damage a car and will void the warranty.

“This really is a significant consumer issue,’’ said Edward B. Cohen, vice president for government and industry relations at Honda. “They’re putting on the market a fuel that cars were not designed for.’’

The E.P.A., on the other hand, cites the importance of lowering oil imports and reducing carbon dioxide emissions from fossil fuels.

A spokesman for the Department of Energy, Bill Gibbons, said that his agency had tested 86 vehicles on test tracks and dynamometers for a total of more than six million miles. “A subset of those engines tested in the D.O.E. study were torn down and inspected with no discernible difference in engine wear between test fuels,” he said.

But the report being released on Wednesday, from a nonprofit technical organization that coordinates research on engines and fuels, the Coordinating Research Council, will describe tests on eight popular engines that were run on an E15 blend for 500 hours. The engines were run at loads and speeds that were intended to simulate the wear that results from 100,000 miles of ordinary driving, the authors say.

Some of the engines were run on ethanol-free fuel (known as E0), some on E15 and some on E20. Department of Energy personnel argue that one weakness of the study is that the engines were not run on E10, which would have provided a stronger baseline.

The study will say that two of the engines showed signs of damage, according to oil and auto executives and government officials briefed on its contents. Muddying the finding somewhat, one of the engines running on E0 also showed damage.

Another point of dispute is what constitutes damage; the study measured leakage from the car cylinders when the piston compressed the air and fuel mixture, just prior to combustion. Government auto experts say that the extent of leakage in the “failed” engines, two of which ran on E15 and one on E20, was typical of cars in service and does not affect gas mileage, horsepower or emissions.

But the oil industry says the E.P.A., which regulates fuels on the basis of the pollution that their usage creates, is relying on a study from the Oak Ridge National Laboratory in Tennessee. The assumption in that study is evidently that if emissions of particulates, unburned hydrocarbons and carbon monoxide stay low, the engine and the rest of the car’s systems will remain intact.

The Energy Department study, which began in the summer of 2007, used cars that were already several years old and had tens of thousands of miles on them; by the end of the testing, all of them had at least 120,000 miles on them.

The study will not publicly identify which engines were damaged.

Industry committees decide on the scope of a study like this one, and the Coordinating Research Council contracts with laboratories to conduct the work. The Energy Department has helped pay for some previous studies run by the council but did not help finance this one. Department officials said that was because of a disagreement over which engines should be tested.

The American Petroleum Institute, a sponsor of the study, said the engines were chosen to represent a wide portion of the cars on the road from the 2001 model year forward, for which the new blend has been approved.

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