E85 corrosion test

In our very unscientific test, we immersed this strip of sheet aluminum in E85 for nine months. We allowed the fuel to completely evaporate followed by full immersion. Note the presence of actual rust on the aluminum. This wipes right off and is probably due to metal particles that were present in the tub when we added the fuel. There was evidence of very minor pitting in the aluminum strip but hardly worthy of comment. The Holley metering block also wasn’t damaged and showed no signs of corrosion. (Image/Jeff Smith)

Hi, I was wondering if you could help answer a few questions and doubts I have about moving forward with my E85 build. I know there’s a lot of hype about E85 being corrosive and I know there are measures to take to make that less possible in the fuel lines, pumps, and filters but I’m wondering about aluminum in an intake or heads or the pistons. What negative effect could that have on those components? Also, if I were to use a 6-71 blower with aluminum rotors, would the E85 damage those? — M.J.

Jeff Smith: Just so everybody is on the same page, E85 is 85 percent ethanol mixed with 15 percent gasoline.

This is a great fuel to use for supercharged engines because not only does it offer a high octane rating of roughly 105, but it also offers excellent cooling opportunities—especially for a 6-71-style supercharger where the carburetors (or fuel injection) is located above the blower.

The cooling effect is much like what can be observed when the nurse at the doctor’s office applies a rubbing-alcohol swab to your skin before a booster shot.

As the alcohol evaporates off of your skin, it pulls heat with it—which is why your skin feels cooler.

The same thing happens in engines.

As the blower squeezes the incoming air and fuel, the large volume of ethanol mixes with the air and pulls a tremendous amount of heat from it. With a lower temperature, the engine runs better because the air is more dense.

We’ve seen a supercharged small-block Chevy drop the inlet air temperature with 8 psi of boost from roughly 140 degrees down to 95 degrees. That’s a huge drop.

Ethanol suffers from a bad reputation due to what we’ll call “guilt by association” with methanol.

Methanol is a wood- or natural gas-based alcohol.

Ethanol is plant-based and distilled mainly from corn. Like sippin’ whiskey or white lightning.

Methanol has a reputation for being highly corrosive when used with non-anodized aluminum, which is true.

Ethanol is non-acidic and is not, by itself, corrosive.

However, ethanol can become corrosive when mixed with water and has a tendency to absorb it.

As a test, we immersed a small piece of sheet aluminum in E85, a test that we started in 2017—nine months ago as of this writing.

The test allowed the fuel to fully evaporate several times, uncovering the raw, non-anodized aluminum and exposing it to the air. We even polished a section of the aluminum just to see if the ethanol would cause corrosion.

NOTE: This is not a very scientific test. But the aluminum was immersed and then allowed to evaporate out of a simple plastic tub, and then refilled with E85 several times.

As you can see in the accompanying photo, there was some actual iron oxide rust that had accumulated on the aluminum.

We believe this is the result of small iron or steel particles that were present when we placed the aluminum in the tub. This corrosion wiped right off the aluminum, but we left it in place for the photo.

We inspected the aluminum carefully and there appears to be some very minor pitting that you would expect to see if the aluminum was immersed and then exposed to the air several times. Our test records indicate that the aluminum sheet over nine months has been through the total-immersion, then E85 fuel-evaporation cycle four times.

NOTE: This test was performed in our shop in Southern California—perhaps in a more humid climate the results might be more aggressive.

To answer your specific question, M.J., we think that if you ran your aluminum heads and blower engine on E85 that you wouldn’t suffer any serious damage to the aluminum parts.

However, it would be a good idea to run the engine on gasoline at season’s end before putting the car into storage.

Ethanol will remove any residual oil from your engine components. Therefore, it doesn’t have the lubricative qualities of straight gasoline. We recommend storing the car with a full tank of gasoline instead of E85 to prevent the ethanol from absorbing water from the atmosphere.

We obviously didn’t attempt to control water absorption in our backyard test.

We also immersed a Holley metering block in the fuel, and it wasn’t damaged either. It is likely, however, that if we had immersed an untreated piece of steel in this test, that it would have experienced significant corrosion.

We were specifically looking to reproduce the white residue that is often found in carburetors after fuel has evaporated. Some contend that this residue is the result of the addition of ethanol.

While we can’t make a specific claim, our test indicates that this white residue is not coming from ethanol.

We think it’s actually coming from the gasoline and not the ethanol. While our test is hardly pure science, it does indicate that much of the claims that ethanol is damaging fuel systems would appear to be more closely related to the aromatic additives currently used in pump gasoline and not the ethanol content itself.

But that’s just our opinion!

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Author: Jeff Smith

Jeff Smith has had a passion for cars since he began working at his grandfather's gas station at the age 10. After graduating from Iowa State University with a journalism degree in 1978, he combined his two passions: cars and writing. Smith began writing for Car Craft magazine in 1979 and became editor in 1984. In 1987, he assumed the role of editor for Hot Rod magazine before returning to his first love of writing technical stories. Since 2003, Jeff has held various positions at Car Craft (including editor), has written books on small block Chevy performance, and even cultivated an impressive collection of 1965 and 1966 Chevelles. Now he serves as a regular contributor to OnAllCylinders.