Optimistic fuel economy?
 

Does anyone else have have a wildly optimistic avg. fuel economy reading on their trip computer? For my last two tanks I had an average reading of 37.8 and 36.5 mpg when I filled up (I reset it every time I fill up) but when I calculated it myself both tanks came to ~31-32 mpg. I still only have 900 miles on mine so I've been driving pretty easy. Maybe it'll get more accurate after the break-in period. And it's a manual tranny if anyone's wondering. I can't complain because these are still great numbers, but does anyone else have inaccurate readings?

Mine has been consistently +2 mpg

All new cars with the comuter calculation always overestimate. This is probably due to rounding. For accurate numbers, calculating itself is your best bet.

I've noticed this to a certain degree. It seems like the average reported by the car is usually between 0 and 1.5 MPG extra. I'm curious if they ignore idling or cheat in other ways :P.

On the flip side, trying to report instantaneous and average MPG without random spikes *and* being spot on would be difficult to implement.

As engee mentioned, calculate it yourself. I just signed up at fuelly and it's really easy to use. I'd recommend it so long as you don't mind giving up data on your fuelling habits.

In my first tank of gas the trip computer was fairly accurate with < 1 MPG overestimate. For my second tank of gas the the trip computer overestimated by about 3 MPG. I had a lot more idling during my second tank because I spent quite a bit of time sitting around trying to get the GPS to work. So, maybe the trip computer is ignoring some of the idling time in its average MPG measurement.

depends on your mode of commute. I mainly do city driving so my avg is 25 mpg total. I have some freeway driving too hence the "higher" avg than the city estimate of 22mpg.

I'm also around 900 miles odo.

I've noticed on the wife's outback that if I hammer on it to get up to speed and then coast vs. a more conservative ramp up to speed it tricks the computer into showing a better average mpg.

Also - there is a program mode to adjust the mpg readout for the outback - to correct it being off - I imagine the procedure will be similar for the BRZ.

mine has been spot on so far. just did my 3rd fill up and i calculated 29.5. then checked the computer and it also showed 29.5.

3 fill ups......avg 34 mpg per tank

I do nearly all city, and im averaging about 24-25.

That's probably what it is then, since most cars with mpg displays usually go blank when you're idling at a complete stop, so it's not averaging moments of 0 mpg.

Mine said I would get 26.6 last tank and I got 30.5 but...I hadn't reset the Ave MPG since I bought the car so thats why. Not helpful I know but I was still pretty happy to see over 30mpg during engine break in (about 800 miles atm).

Last fill up said average = 28.8, actual by the math 28.7. :shrug:

The MPG on the trip computer is the average mileage you got since the car was first driven, unlike other Subaru's it's not tied to trip A or B that will reset when you clear your trip. You may have gotten 37MPG since you've had the car, but the last fill-up was under the average for the car.

With me, my average is 0.8MPG higher on the display than it actually is.


EDIT: Unless there is a way to manually reset the average MPG?