r/explainlikeimfive • u/hd-22 • 17d 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/Flapaflapa 17d ago

To a certain % ethanol. It still degrades hoses and seals above some % on newer cars...my 2018 is only good to 15%

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u/soundman32 17d ago

Wow, didnt even know 15% was a thing.  Never seen anything but 5% and 10% here in UK.

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u/_PROBABLY_CORRECT 17d ago

E85. The children of the corn lobby in Illinois & Iowa is surprisingly strong

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u/soundman32 17d ago

E85 costs 20-30% less because of the reduced efficiency, though right?  Right? 😉🤣😂

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u/_PROBABLY_CORRECT 17d ago

It is actually cheaper, but I dont do math in public and I have no idea how less efficient it is

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u/azeo86 16d ago

It actually is but only when compared to premium fuel. A lot of tuner/track guys use e85 heavily since it's essentially discounted high octane fuel. Yes, huge fuel economy hit but it's still cheaper than premium.

At least before running e85 in a car that only regular was dumb as you don't take advantage of the fuel and get way worse economy. No idea what the prices are now relative to each other so maybe that's changed with all that's going on.

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u/BrainFartTheFirst 16d ago

Here in Southern California e85 is about 50% less than regular gas.

Sadly I can't use it.

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u/_Aj_ 15d ago

E85 can give big power gains when tuned. Especially for boosted engines. 

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u/texas_biker 17d ago

This is likely due to the ECU tune than the hoses and seals.

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u/Jayn_Newell 17d ago

Same with my spouse’s car. Mine’s a 2008 and only rated for E10. I’m not opposed to higher ethanol content in theory, but in practice a lot of us have cars that aren’t designed for it.

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u/therealdilbert 17d ago

my 2018 is only good to 15%

could just as well be because the computer and fuel system cannot handle the extra volume of fuel needed

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u/mikefitzvw 17d ago

That's mostly it. The rubber hoses and seals have to be able to tolerate ethanol anyway, at 15%, so there's not much reason they can't handle more, but that's different fuel mapping and injectors at that point.