Last updated on 2011.08.18
Monday before last, I drove out to Spearfish and got a job. Last Monday, I drove out to Spearfish and got an apartment. This coming Sunday, I haul family, teacher shoes, and bicycles to Spearfish. Work starts this coming Monday.
Among the joys of five traversals of the great state of South Dakota in 14 days is the opportunity to test my 2002 VW Beetle's gas mileage. I've used 89-octane 10% ethanol blend pretty regularly since the 1990s, largely because my taxes already paid for some of it and because it's usually the cheapest juice at South Dakota pumps. Paying 20 or 30 cents more for 91-octane premium.
The following data from five tanks of gas in the trusty Bug have me wondering if maybe I ought to switch to premium. The columns tell you...
- where and when I bought the gas;
- what type of fuel (10% ethanol or no ethanol, then octane rating);
- price per gallon (rounded up!);
- miles per gallon;
- at that mpg, how many gallons would be needed to go 400 miles;
- at that pump price, how much that 400-mile trip would cost;
- what roads I took (matters, since I went 60-65 on SD-34, 70-75 on I-90).
|$/gal||mpg||gal to go
|cost to go
|HumDinger2, Wessington Springs, 8/8||Ethanol-10/89||$3.68||28.46||14.05||$51.70||SD-34/I-90|
|Speedy, Spearfish, 8/8||no eth./91||$3.90||37.51||10.66||$41.58||SD-34|
|Fresh Start, Pierre, 8/8||E-10/89||$3.60||32.22||12.41||$44.67||SD-34|
|Jake's Corner, Winfred, 8/15||E-10/89||$3.42||31.28||12.79||$43.72||SD-34|
|Safeway, Spearfish, 8/15||no eth/91||$3.90||35.31||11.33||$44.16||I-90/SD-34|
Now there are all sorts of factors to confound hard scientific conclusions, not the least of which is the fact that I never drained the tank completely before adding new fuel (unwise, especially on Highway 34 west of Pierre!).
But my first tank of 91-octane, zero-ethanol gas from the Spearfish Speedy station by Exit 14 produced a pretty clear mileage advantage, giving me 37.5 miles per gallon. The same product from Spearfish Safeway gave me 35.3 mpg. Not bad, considering that over 5500 mild-weather miles since May, the Bug has averaged 31.7 mpg.
The best mileage I've gotten on 89-octane, 10% ethanol blend came on a fill-up I bought from the Madison BP in May. I drove across Minnesota on Highway 14, stayed under 60, and coasted into every town. That got me 34.0 mpg.
Now the real metric that matters isn't how much I pay in one visit to the pump; it's how much it costs me to cover a certain distance. Compare Speedy's 91 with Jake's 89. Speedy's gas cost me a premium of 48 cents per gallon. But I burned so much less of it at 37.5 mpg that, on side-by-side 400-mile trips, the high-octane, no-ethanol fuel from Spearfish would have saved me $2.14.
Jake's gas still beat Safeway's for total 400-mile cost by 44 cents. But at the point where my savings won't buy a Hostess pie, I turn to other factors. Do I do the Earth a favor by burning less fuel? Does that extra 44 cents leave my engine cleaner than regular gas with a shot of corn whiskey?
I would enjoy hearing your experiences, dear motoring readers, with different blends and grades of gasoline and ethanol. I'll keep you posted on my mileage data, but be forewarned: living five blocks from the office and the grocery store is going to reduce my dataset significantly. And for once, I'll be thrilled to have less data.
Update 21:34 CDT: One thing I don't want to have to factor into my mileage calculations: baseball-sized hail near 1880s Town on I-90! Ouch!