Does Ethanol actually corrode metals and plastics?

What if we told you ethanol isn’t the only substance present in gasoline that can cause issues in your older car? Scary stuff, huh?

Ethanol, usually up to 10% by volume, can be found in today’s pump gasoline to add octane while also reducing the dependence on fossil fuels. While ethanol can absorb moisture–possibly leading to issues in cars that sit–most consumers burn through a tank quickly enough to avoid any damage. 

But what dangers does the ethanol itself possess? Ethanol brings oxygen into the structure, notes Zachary J. Santner, senior specialist of quality at Sunoco. “That oxygen is more reactive than gasoline and can cause oxidation in some cases.” But, he continues, pump fuels also contain corrosion-fighting additives to offer protection from the pipeline to the car. 

For some additional data, Santner points to 2008 studies by the Minnesota Center for Automotive Research at Minnesota State University, Mankato, on the effects of E20–gasoline containing 20% ethanol by volume–on the metal and plastic components commonly found in fuel systems dating back to the ’70s.

Out of the 19 metals tested, only one experienced pitting when exposed to E10 and E20: unplated Zamak 5, a cast zinc found in some older carburetors. (The study notes that Zamak 5 is often plated to make it more corrosion-resistant.) The test also found the ethanol-enriched fuels to only cause issues with plastics not commonly found in fuel systems: ABS, PVC, PBT and polyurethane. 

So, how could a non-ethanol fuel wreak havoc on your car? Gasoline is formed from hundreds of different hydrocarbons, Santner explains, with each component selected for the specific mission. Too many of the energy-dense aromatic compounds, for example, could degrade rubber seals. 

But not to worry, he says. This is why gasolines are blended according to specialized recipes with certain doses of each ingredient, as too much or too little of any of them can cause issues. His practical advice: Worry less, drive more and don’t forget that non-ethanol fuels are available.

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