What Does the Computer Know?

When I was growing up, my parents kept a small notebook in both cars where the odometer reading and fuel purchased were recorded, along with oil changes and other maintenance items. We always, always, always filled the tank. By recording the fuel usage and calculating the mileage, you might notice because of a sudden drop that something was wrong, even before you had any other signs. And I suppose it's just something that people used to do. Driving wasn't always a hop-in-the-car-and-go affair, and perhaps keeping the log was a leftover from the early days of motoring. I still have the note pad that was used for a couple of the cars.

After I got married, I dropped the practice, largely because my wife didn't participate. That was one of the first times I realized that just because my family had always done something, that didn't mean it was strictly necessary. Even though I quit logging it, I almost always fill up, and calculate the mileage if the vehicle had been filled up the last time. With the Traverse, it isn't always possible to fill up because one gas station I go to stops at $50.00, and depending on the price, that may not be quite a full tank.

The Traverse is the second car we've had that calculates your mileage for you. The calculation is made based on fuel flow rate and speed. The first car that did this was the '85 Corvette, the first car we had with any sort of computer-driven display. I seem to recall it being fairly accurate, and I've had people tell me that their experience is that the computer is accurate. I've been checking it closely in the '06 HHR that I bought  few weeks ago, and the computer doesn't do such a good job.

The results from the first five complete tanks are as follows:

Miles/gallons = mpg; computer est.
433.9/15.6 = 27.8; 27.4 (not far off)
371.2/14.4 = 25.8; 27.9 (more in-town on this one)
404.3/14.4 = 28.1; 28.9 (more highway on this tank, since I drove to my parents' house)
412.6/14.9 = 27.7; 27.9 (close again)
382.3/14.1 = 27.1; 28.5

I don't know what happened on that last tank, unless it was excessive stop-and-go traffic. But the computer guessed high.

I was really hoping to get around 30.0 miles per gallon with this car. I got 33 with the air conditioner in the Saturn, and 36 without. Maybe in a few weeks I'll be able to see what this car does when I don't need the a/c in the mornings. However, this car has a 16.5 gallon tank, so I can easily go over 400 miles on a tank. The Saturn would give me 400 miles without the a/c, but in the summer time, 400 miles was really pressing my luck.

Later, I'll post regarding the effect of using the air conditioner versus having the windows open. Believe it or not, that's a controversial subject.