Asklemmy @lemmy.ml Hurculina Drubman @lemm.ee 4 mo. ago

why do a bunch of gas stations have 88 octane cheaper than 87?

I figured it was a marketing gimmick to get you to buy 88 and then they would finally raise the price, but it's been years. are they adding extra ethanol or something?

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That cheaper 88 octane fuel is a blend of 85% unleaded gasoline and 15% ethanol. It's also known as E15 fuel.

The ethanol is an oxygenate: it adds oxygen atoms to the fuel mix so the fuel burns more completely. That's good for vehicle emissions. However, the ethanol is less energy dense than gasoline so you will get slightly worse mileage.

https://www.motortrend.com/news/what-is-e15-gasoline-pros-cons/

https://www.cleveland.com/news/2023/05/cheap-gas-lower-mpg-are-unleaded-88-and-flex-fuel-more-expensive-in-the-long-run-saving-you-money.html
- does it still eat away at your seals or have they fixed that
  
  Both. Ethonal is still corrosive and the majority of fuel systems these days are compatible with E15. That said, check your owners manual.
- okay so I had AI do the math for me.
  
  the 88 octane fuel with 15% ethanol would need to be approximately 4.7% cheaper than the 87 octane fuel with 10% ethanol to compensate for the lower fuel efficiency caused by the higher ethanol content.
  
  okay so I had AI do the math for me.
  
  "I drove a screw with a hammer"
  
  Years ago I had an E85 compatible vehicle when that was how we were going to save the planet before hybrids came along. E85 was cheaper than unleaded, but after crunching the numbers it was always the exact same cost per mile. Considering there were almost no stations with E85 fuel available, it just never made sense to go far out of my way to pay the same.
  
  AI is decent for writing, but a terrible choice for math.
are they adding extra ethanol or something?

Yes. 88 has up to 15% ethanol. You should check your manual before using it.
Yes. 88 Octaine is 15% ethonol instead of 10%.
- Isn’t summer fuel E0?
  
  If anything, it would make sense to have gasoline with ethanol content in summer because ethanol is more knock-restistant, which you are more prone to if tempereatures are warmer.
  
  summer fuel?
Octane is a measure of how prone to knocking the fuel is, not energy.

Knocking is premature combustion, I.e. why lead used to be added.
- holy fuck you're right. I always knew that higher quality fuels reduced knocking, but I thought it was a side effect of the fuel being more pure or something. I haven't really put any thought into this since I was a kid

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