QUESTION: I've checked the mileage on my car several times, and I come up with completely different numbers. Is there a way I can get a really accurate idea of the mileage?
--Cathy L. Brawn, Lake Mary, Fla.
ANSWER: For a baseline, look up your vehicle at Fueleconomy.gov. You'll find it lists the EPA-rated mile for city and highway, which -- let's face it -- is impossible for us to duplicate. But click on the name of the car, and it gives you the overall average mileage: A 2009 Chevrolet Impala might be rated at 19 mpg city, 29 mph highway, but click on the Impala's name, and you'll see the overall average is supposed to be 23 mpg. So that is what we are shooting for.
Here's how I do it: I fill the gas tank at one particular pump, at one particular gas station, and let the nozzle shut off the gas flow -- I don't try to keep squeezing in the gas. I then follow a set 40-odd-mile loop that covers some city, some country, some highway driving that leads back to that same gas pump. Then I fill up again, and let the nozzle shut off the flow -- using the same pump is helpful, because some nozzles are more sensitive than others. Take the reading of the gasoline you used, and divide it into how many miles you drove.
If you used two gallons and drove 40 miles, you got 20 mpg. Even if you have a trip computer than gives you a mileage readout, I suggest checking it with this method -- I've seen trip computers that are as much as 10 percent off. If your mileage is, say, 15 to 20 percent worse than the EPA suggests (it will likely be a little less because we are stuck with E10 ethanol gas), consult your mechanic.
