I use a app called car scanner and it's kind of cool. It tells you what your gas mileage is on trips. I recently drove 1500 miles, the last two days nearly. I assume nothing is more accurate than just calculating how many miles you drove and how much Gas you put in the tank. If so, it looks like this app is easily 10 to 15% off. And even the instant calculation on the car – is off. Does that sound about right? This 40ish stretch is me running a crowded section of i40 likely having to slow down or speed up to maintain my spot- but most times around 78-81mph. I was thinking I was thinking I was getting 50+ on my 50 mile trip to work if I kept it under 60 on the highway- but I'm probably only getting like 44mpg. Why does it matter lol- because I want a truck! I'm cheap, and I see a Honda ridgeline (2017+) in my future. Maybe in a few more years if we find the the Ford Mavericks to be any good long term, that might be an option.
When I bought my car new, I was curious about how accurate the MPG number shown on the dashboard. Over 10 - 20 fillups, my calculated MPG was always smaller than the dashboard MPG. It was about 5% smaller, not 10-15% off. I also did the same thing on my Prius C. The discrepancy was about 3% though.
Don't know how your going to handle going from 40+mpg down to 20-25mpg in a Ridgeline. I have a very difficult time when I'm driving my 4x4 Envoy-XL at 18mpg. I figuratively have to stop at every gas station along my camping & fishing route.. Yes; the car's ECU calculations is overly optimistic and the odometer is displaying a few miles faster than actual travel. You can verify this by using GPS mapping over a straight level highway stretch of 5+ miles.
