November 16, 2009
In the three months or so since Sibylle and I purchased our Honda Insight Hybrid, we have averaged about 43 MPG for each tank of gas. The car's computer has a number of displays providing all sorts of information about the car's performance and gas milage. One of the displays shows the current miles per gallon for the tank of gas in use, as well as an instant MPG graph.
I tend to leave the computer set to this combined display as it shows me how I am doing at the moment as well as how the MPG rating is fairing for the current tank of gas. Fairly early on in driving the Insight I discovered that there is a bit of entropy in my route to and from work. There's a big hill I go up on the way to work, and back down on the way home. It would seem logical that whatever milage was lost climbing the hill would be regained coasting back down it. While this equality is possible, it is not guaranteed. If you are at all aggressive about climbing the hill (the speedometer glows green if you're being economic and a bright blue if you aren't) you can't regain the lost miles per gallon on the way back down.
The game I play is too see how little if any I lose on the overall tank rating on each outing. Most trips to or from work I can stay even or at most lose 1/10 (0.1) MPG. Some days, when I catch all the lights and can maintain momentum, I can gain a tenth or two. Obviously the longer it has been since the last fill-up, i.e., the more miles on a particular tank of gas, the harder it is to improve the average.
Today all of this changed dramatically. Today is the first seriously cold day we've had. The high was only about 36º and the performance impact on the Insight was dramatic. When I backed out of the garage this morning the tank average was 43.3. And the tank only had about 5 miles on it. By the time I arrived home for lunch this figure had dropped to 36.0. This evening when I got home it was 35.8. I believe that I didn't drive any more aggressively than I usually do, if any thing I was more cautious as it was sleeting or raining or snowing while I was driving.
One of the interesting characteristics about our hybrid, and I guess most others, is that the gas engine turns off at red lights since it isn't needed. With it colder outside the car didn't shut off once on any of the trips to and from work or the store. My guess is that in order to heat the cabin comfortable the gas engine needs to run, so I am suspecting that our wintertime gas milage is going to be in the mid-30s rather than the low-40s.
So my score for today was -7.5. Ouch.