Several times, in various threads, people have been told that they should not rely on the onboard MPG readouts on their dashboard, due to a lack of accuracy from these devices. I am currently driving my first car that is equipped with one of these devices, and after almost 2 years with this car, I finally decided to verify the accuracy of that readout.
The result, over several tanks, was that the onboard readout IS optimistic…to the tune of 1/2 of 1%.
Ergo, accurate enough for most people’s uses.
For example, on my last tank of gas, the dashboard MPG readout was 26.1 mpg.
When I calculated my actual mileage with paper and pencil (and with a calculator, just to verify things) the “real” figure was 25.85 mpg–a difference that is, IMHO, statistically insignificant.
So, while I can’t speak for the accuracy of these devices in general, I can tell you that I have found mine to be…acceptably accurate.
What type of experience have other forum members had with these devices on their own cars?