I thought it would be interesting to compile everyone's data of dashboard MPG vs manually calculated. The first time I checked mine the hand calc was about 0.8 mpg above what the dashboard read.
I created a google doc spreadsheet for everyone to punch in their info.
To keep everything as repeatable as possible everyone should follow these guidelines:
- Have a 2011+ 5.0 Mustang
- Next time at the gas station, fill up until the auto-stop pops once
- Reset one of the trip odometers
- Reset the Avg. MPG
- Fill up the same way, write down the Avg. MPG from the dash
- Divide the trip mileage by the # of gallons shown on the pump and write that down
Feel free to contribute as much as you want, as long as you haven't strayed from this procedure, or fudged the numbers. Once there is enough data, we can graph it and see if there's a trend. I added a column (Y/N) for having a cold air intake and/or tune, and one for the octane rating since those can have an effect too.