Crunching the numbers

I’ve been somewhat anal about logging my fuel consumption since getting my new car. I have three different calculations going, which shows how numbers are hardly incontrovertible facts these days.

The car itself displays cumulative, trip and instant miles per gallon but I think it’s somewhat optimistic by a few mpg. When I fill up, I log my purchases using the GasBag app on my iPhone; it has a confusing interface and doesn’t show me what my efficiency is per fill up, but only over time. Last, I do the math myself.

Here’s how my new Jetta TDI has performed since the first time I filled it up (I discarded the data for the tank that it came with from the dealer):

As you can see, the fuel economy has steadily worked its way up over time; I’m told that the mileage will continue to improve into the 50s as I get into the tens of thousands of miles. Which could well be 6 or 7 years from now. I’ve had the car 3 months now, and haven’t managed to put 2,500 miles on it yet.

I’ve also become less paranoid about filling up before I reach 1/4 tank. Yesterday I filled up when it hit the red zone, and it still told me I could go another 80 miles on what was left.

Thankfully, with prices plunging, my per-mile cost has gone from 11.6¢/mile in September to 7¢/mile now. Considering that my Audi got 25mpg and cost something like 16¢ per gallon… well, looks like I might have made a pretty good choice. Still, I’m waiting for those vaunted numbers that best the Prius, the ones that the forums are buzzing about. When I’m driving along and the display says I’m getting 67mpg, I feel smug; but when I check the cumulative average and it says 38, I’m dismayed. Having a diesel is obviously a long-term thing.

I’ll be taking a road trip to LA at the end of the month, so that’ll do some breaking in. And at 7¢ a mile, it’ll only cost me $28 to get there. Less than half the cost of a Disneyland one-day, one-park ticket. Bargain!