Car Mileage meter - how accurate

We’ve used a number of different cars via ZipCar over the years, and have always paid attention to gas mileage on long trips (we’re computer nerds - we just like thus stuff.) We found the readouts to be quite accurate. Our current Hyundai Elantra has also proven to be accurate. No reason they shouldn’t be, with modern fuel injection systems controlled by computers metering the fuel delivery constantly.

All through my childhood my parents had an annual logbook in every car we owned and kept track of every gallon used and mileage. You could get the little books from gas stations. At the end of the year my dad always ran totals. My mom no doubt still has all of those records somewhere.

We also kept special logbooks for vacations, with notes on campgrounds we stayed in, when we got up, miles traveled, any sightseeing that day, temperature in the morning, stops for groceries, where and when we went to Sunday Mass, and a lot more. My dad was so geeky.

I believe that idling is taken into account when the computer calculates mpg. Remember at idle the motor is only running at 800 or so under almost no load, therefore it uses only a minuscule amount of gas, compared to traveling down the road.

When I idle away at least 1/2 tank of gas and it still reads 26mpg for that tank, pretty sure it’s not being factored in.

Mileage meters have accuracy that was suspect in my experience. Their biggest value is denoting change rather then absolute value. IMO, most gauges are of value in this way.