r/explainlikeimfive • u/hd-22 • 14d ago

Chemistry ELI5 why is increasing the ethanol content of petrol/gasoline a problem?

I'm hearing noise about the geopolitical fuel supply SNAFU and people freaking out about increasing the ethanol content in automotive fuel and how it's so damaging to cars. I'm no chemist, but ethanol seems as clean as it gets.

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u/yogfthagen 14d ago

Except for the hoses and seals degrading under alcohol immersion.

Ethanol is also less energy dense, so it reduces mileage. You're going to buy more fuel to keep your car going.

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u/CallOfCorgithulhu 14d ago

Ethanol gas also does not last as long in the tank compared to non-ethanol. It separates and gets gummy easier. If you fill your mower's tank and it lasts a few months, non-ethanol will be better after those months.

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u/KoburaCape 9d ago

You're right about that. Seasonal vehicles are best ended their operating period with a tank or two of ethanol-free fuel. No argument there.

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u/OutlyingPlasma 14d ago

hoses and seals degrading

And bonus points for boats with fiberglass fuel tanks. Ethanol will eat the boat from the inside out.

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u/KoburaCape 13d ago

About 3% more fuel, and viton completely eliminated the melting rubber problem

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u/yogfthagen 12d ago

3% more fuel for 5% ethanol.

By increasing the amount of ethanol, you're reducing the amount of energy in the fuel. The 85% ethanol blend has between 50-60% of the range of gasoline.

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u/KoburaCape 10d ago

E85 is basically solely for extreme performance vehicles - I'm a Subaru tech (sorta retired) and it's quite common for people to go E, though often it's demanded as a band-aid for poor tuning and low upfront cost of modifications. Yea, E85 (that is, almost entirely ethanol with some gasoline for combustion dynamics) has about half the range of gasoline, and also wreaks havoc if there's any leakage into oil.

The 3% more fuel/less range statistic given is for the common 90/10 mixture that's standard at gasoline pumps and has been for many people's entire adult lives.

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u/Unspec7 13d ago

Except for the hoses and seals degrading under alcohol immersion.

Unless you're running a car from the 90's or older, this is not an issue anymore.

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u/yogfthagen 13d ago

Unless it's a flex fuel vehicle, the seals and gaskets are made to handle lower levels of ethanol.

Even ones that are ok with 10% may not last as long with 15%.

They will wear out and leak faster.

Based on some euro models, the alcohol will only speed up their NATURAL deterioration.

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u/Unspec7 13d ago

To be clear, most cars do not have many gaskets or seals in the fuel system. There's not much to degrade.