[314]

Car computer MPG waaaaay off?

my tripometer said 240 miles.
mpg screen on infotainment system said 37mpg avg. (I reset it every time I fill up.)

I filled up 8 gallons.
240/8 = 30mpg!

huh?

 

[nanxun]

Wow, that's a big discrepancy. My carputer has been consistently off (about 1.8-2.0 mpg HIGHER than figures I get doing my own calculations). But lots of other folks seem to think their computers are pretty accurate (see thread below).

http://mazda3revolution.com/forums/2014-2016-mazda-3-skyactiv-discussion/122362-how-accurate-car-s-avg-mpg-calculator.html

 

[ElNino77]

Mine has been pretty consistent with Fuelly as far as total MPG, give or take. Although it seems my trips are all much higher than my total average, so i dunno WTFIGO. Basically i've just accepted i get around 27-28 mpg driving the way i do with the 2.5L manual

 

[pete_89t2]

2014 M3, 2.5L (S-GT hatchback) here. My computer average MPG readings tend to be 0.5 to 2 MPG higher than my manual calculations on a consistent basis.

I always fill my tank, and I always reset the computer's average MPG reading when I fill up. Part of the discrepancy is due to the fact that when I fill up, I completely fill up; i.e., when the pump shuts off, I pull the nozzle out part way, give it about 10~15 seconds for the tank to vent & gas to settle, then I start the pump again. Repeat process till it won't take anymore, which is typically 1~2 pump restarts.

The computer bases it's calculation based on the tank's volume specification; if you fill up completely like I do, then the tank and some portion of the filler neck is full. That extra gas is not accounted for in the computer's average MPG calculation, but it is counted in the manual calculation (miles traveled/fuel used), so the manual MPG calculation will always be a bit less than the computer's reading.

FWIW, mine averages 32~33 MPG if I do nothing but commute to work, which is mostly 4 lane highway (55~65-ish, a few lights in between), with some stop & go traffic at each end.

 

[RoboRaccoon]

I was quite surprised the last time I filled up. Trip computer says 7.7L/100 km but odometer and gas bill says 6.9L/100 km. Quite happy despite the error

 

[g60_corrado_91]

I had the ECU recall done and I'm not sure if it changed anything with the infotainment fuel economy app, but it seems more accurate not i.e. not reading as high as it once did. The overall fuel economy on the cluster itself is at 37.0 right now and my overall Fuelly average over 14k is 35mpg, so it's a couple higher. But it was much higher reading on the fuel app itself from day to day driving.

What is really off is the miles until empty. I've driven 20+ miles on "0" range and filled up, only to have the pump clicking at 10 or so gallons. Do the math, 3.2 gallons *35mpg = 112 miles PLUS the 20 miles I drove on "0." That's frustrating especially when you're on a road trip and don't want to push it in case the computer is correct, but in reality, can go another 100+ miles...

2015 iSport 6MT HB

 

[314]

I had the ECU recall done and I'm not sure if it changed anything with the infotainment fuel economy app, but it seems more accurate not i.e. not reading as high as it once did. The overall fuel economy on the cluster itself is at 37.0 right now and my overall Fuelly average over 14k is 35mpg, so it's a couple higher. But it was much higher reading on the fuel app itself from day to day driving.

What is really off is the miles until empty. I've driven 20+ miles on "0" range and filled up, only to have the pump clicking at 10 or so gallons. Do the math, 3.2 gallons *35mpg = 112 miles PLUS the 20 miles I drove on "0." That's frustrating especially when you're on a road trip and don't want to push it in case the computer is correct, but in reality, can go another 100+ miles...

2015 iSport 6MT HB

the car can display avg mpg since mile 0?! HOW??

and the car has about 2.5 gallons left after all the fuel bars are gone.
2.5 x 40mpg = 100miles (hwy)