The Great Gas Experiment – Update 1 (2013-03-15)

Update 2013-03-15: Edited to correct a math error I noticed that was due to a typo when calculating the cost per mile.

Today marked the second filling of the car with alcohol-free gasoline, and the end of the first tank.

  • 12.17 gal @ $3.699 / gal = $45.01
  • Distance traveled = 279 miles

Preliminary results?

According to my car’s trip computer, there’s a definite improvement. For the last couple of tanks of adulterated gas, the car’s computer has calculated that I’m getting an average of 23.8 mpg. Today, when I went to fill up, it said 24.5 mpg. The caveat? I don’t know what time frame / mileage range it calculates that over, so it could be reading low due to including data from adulterated gas.

According to the Fuel Log app on my phone, I got 22.93 mpg on this tank, which is lower than my previous two fill-ups. However, I also think I “stuffed” a little more gas in than usual trying to get up to an even dollar amount (which, of course, I overshot by one frelling cent), which would make it look like it took more gas than it did to go that distance. (FYI, it is, according to the owner’s manual, an 11.9 gallon tank.)

At this point, I think my car’s calculation is probably more accurate than my phone’s calculation, so it looks like I may be getting a noticeable benefit from the alcohol-free gas.

Like last time, the cost at this station is more expensive than at my usual Kroger station – $3.699 / gal compared to $3.489 / gal at Kroger. However, today I noticed that there is a full service lane at this station, and they charge the same for full or self-serve. That adds a little convenience to offset the additional cost, if I want to take advantage of it.

The cost analysis, based off my car’s mileage estimates:

  • 23.8 mpg = 0.0420 gal/mile * $3.489 / gal = $0.1465 / mile
  • 24.5 mpg = 0.0408 gal/mile * $3.699 / gal = $0.1509 / mile

That works out to a difference in cost of $0.0044 / mile in favour of the alcoholic gas. But remember that this is a very preliminary conclusion, since my “sample size” is so small. And I would again point out that my car’s computer may still be using some data from before the switch, so the actual mileage for alcohol-free gas may be even higher, which would probably put it ahead of the regular gas.

Distance per tank and cost per tank estimates:

  • With alcohol: 11.9 gal * 23.8 mpg = 283.22 miles | 283.22 miles * $0.1465 / mile = $41.49 / tank
  • Sans alcohol: 11.9 gal * 24.5 mpg = 291.55 miles | 291.55 miles * $0.1509 / mile = $43.99 / tank

Notice that, despite the ~$0.20 / gal difference in cost, it’s only about a $2.50 difference in cost per tank. Not enough that I would really consider it to be significant, especially when the added wear and tear on the car from the alcohol is considered – yes, as a 2008 model my car is supposedly designed to handle it, but I strongly suspect that it’s still going to have a negative effect on the life of some parts.

If you see any errors in my methodology, or in my math, please mention it in the comments. However, note that this is not a truly scientific experiment. My “control” consists of not making any deliberate changes in my driving habits, which does not equal driving exactly the same for every tank of gas.

I have not made any conscious effort to change my driving habits or style in any way, but minor changes in schedule, weather, etc., may mean that this one tank is not representative of any true change in fuel consumption. I’ll have another update after my next fill-up.


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  1. Miscellany | Curses! Foiled Again!

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