Sparky: MPG Update

Sparky has a few more miles on her, and so I wanted to give an update on her gas stats.  Why the gas stats, and not the battery?  There are three reasons:  I don’t have any electrical consumption data right now*, I would like to know the cost of a long road trip (which would be mostly gas-miles), and the lack of a clear MPG number just plain annoys me.

*Electrical consumption data is now available here.

What I mean is that the car itself, and the related OnStar apps will tell you that the vehicle has traveled (for example) “211 Miles Per Gallon“, which is such a misleading statement that I find it offensive.  While the car may have indeed traveled 211 miles for each gallon of gas burned, that has nothing to do at all with the total operating cost of the vehicle.  My Jeep’s computer will tell me that I’ve used, on average, 13 MPG.  That’s a very useful number, because I can easily figure out, for example, the cost of my round-trip commute using current gas prices.

To make things yet more perplexing for the Volt, even when operating with the gas engine, the “buffer zone” of the battery is being consumed at times.  That means that the Volt at that point is using a little bit of battery for every mile, at least until the battery is drained to the minimum of the buffer zone.  Only then could a “true” MPG for the vehicle be obtained.

I’m going to do my best here, however.  The source data for the numbers below comes from the Volt itself which is about 15 miles away from me right now, via the OnStar app for the Droid (awesome):


1545 Total Miles

– 1336 EV Miles

= 209 Gas (“Hybrid” maybe a better term) Miles

Current Gas Status

29% Tank Level

* 9.3 Gallon Tank Size

= 2.7 Gallons Remaining

or, 6.6 Gallons Consumed

Hence, the “actual” MPG is:  31.7

That figure is a little off from my estimate of 40.7 MPG in the original post.  I think that’s due to excessive rounding (I had used the “Fuel Left” figure, which is only accurate to the nearest whole number), and perhaps a different driving style (we did a lot of gas highway miles when Sparky was brand new — less so more recently).

As for this latest figure of 31.7 MPG, I have to add a couple of disclaimers about its accuracy:

  • I don’t know that the 9.3 gallon tank was topped off to exactly 9.3 gallons when originally filled.
  • I don’t know the accuracy of the “tank level” number (does it include a safety margin like most fuel systems where you have some cushion to run “below the E“?).
  • I  don’t know how much “buffer” battery was used.

Finally, I can’t really say what the mix of highway vs. city driving might have been up until now (I’m going to guess around 60% and 40% respectively).  So please take this number as a reasonable approximation of what you can expect for your Volt’s gas consumption.

Incidentally, I just checked our window sticker, and it promises 37 MPG (combined city/hwy) “when electricity is used up“.

I just completed my two metered charging projects, and so I should have some electrical consumption data shortly:

Chevy Volt Metered Charging (Phase I)

Installing Our New 240V/Level 2 Voltec Charge Station (Phase II)

About Scott

I'm a computer guy with a new house and a love of DIY projects. I like ranting, and long drives on your lawn. I don't post everything I do, but when I do, I post it here. Maybe.
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One Comment

  1. Omg! Gas mileage! I luv it!

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