2007 Honda Civic Long-Term Road Test

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2007 Honda Civic GX: Cold Nights = More MPG

March 03, 2009

2008GXngv.jpg

What a difference a change in the weather can make!

I've been watching the GX's fuel economy pretty closely the past few months (while studiously avoiding writing about it, to the chagrin of several editors around here!) and can now report with the authority of numbers that although the daily drive hasn't changed, fuel efficiency has improved markedly as nighttime temperatures have dropped.

It all goes back to nature of the Civic GX's natural gas fuel - its molecules expand when warm and contract when cold. The tank, which holds the equivalent of 8 gallons, will contain more natural gas, by weight, when the fuel is pumped on a cold day (or night, which is when we fill up) than on a warm one.

Anyhow, the GX averaged 35.77 miles a gallon over the last 2,719 miles, from Dec. 17 through the most recent fill-up on Feb. 26, a period when nighttime temperatures (we fill up overnight) regularly fell below 45-degrees Fahrenheit.

That's almost 5 percent better than the 34.07 mpg average we recorded for the previous 3,347 miles, between Sept. 30 and Dec 16, when nighttime temperatures in our area were in the high 50s and low 60s.

Continuing our backward march through time, the GX averaged 31.68 miles a gallon for the 11,256 miles before that - Feb. 28, 2007, through Sept. 29, 2008, a period of even warmer nighttime temps .

We're not going back any further because Feb. 28, '07, was when we started using the Phill home natural gas fuel pump, which delivers a denser fill-up than the retail pumps we'd been using since the GX came into the Edmunds Inside Line long-term fleet on June 29, 2007.

(If you are curious, our average for that initial period, covering 12,255 miles, was a flat 29 mpg and our average since, for 17,240 miles, has been 32.79 mpg).

And to reiterate, almost all of the driving, save for two weekend mini-vacation drives, has been on Southern Caliofrnia freeways and most of that during the morning and evening rush-hours. We do get to use the carpool lanes, however, so there's been a bit less fuel-wasting, stop-and-go driving than if we were out there in the scrum every day with the rest of the mob.

Oh, and for the whole time we've been using the home fueling system, we've been averaging under $2.25 a gallon-equivalent for our natural gas and the electricity to compress and pump it, even when regular gasoline was up over $4 a gallon.

For the past few months, with gasoline in the $2.10-$2.40 range here, our CNG fuel at home has run well under $2 a gallon.

John O'Dell, Senior Editor, Edmunds Green Car Advisor @ 29,479 miles

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