Live MPG fluctuations

[rogueit]

We just purchased a 2009 legacy and were looking at the trip computer. It fluctuates from 99.9 to 17.0 MPG. Now while 99.9 mpg would be nice, I don't believe that it is correct.

Is that display supposed to be so massively wrong?

Is this effecting the Average MPG and distance to empty?

How do I reset the computer to start a new average?

 

 

Thanks,

Rogue

[brum]

The "rolling" fluctuations is kinda dumb if you ask me. It is only telling you second by second. The Till Empty Distance is based on your Ave MPG.

 

To reset the Ave MPG just reset your odometer. What's nice is you can have two different Ave MPG. One for each Trip A and Trip B.

[Underdog]

Yeah, in case you aren't aware there is instantaneous mileage and average trip mileage, as mentioned above.

 

If you reset the trip mileage by resetting the trip odometer, it will closely follow the instantaneous for a little bit and then will settle down as you add on the miles. Unfortunately the trip odometer will roll over at 10,000 miles though and you will start again.

[92 Legacy LS]

I actually don't think the instantaneos is dumb. I use it to monitor my driving habits and try to keep it as high as possible. When I am working at it, taking off slow and coasting a little more than braking, it can have a substantial impact on overall mileage, 2-3 mpg on a tank.

[joeblow]

The idea is that 100 mpg is no throttle and about 2 is WOT. ^ Like 92 Legacy said, it serves as a reminder or cue to how hard you're mashing on the pedal and how your personal driving habits can affect overall mileage.

 

Average is just that... an average of your instantaneous over the course of the trip odometer. It makes for a decent guess if you don't calculate your own mpg by dividing the miles driven by the number of gallons you put in between fill ups.

[B-Power-B]

It makes for a decent guess if you don't calculate your own mpg by dividing the miles driven by the number of gallons you put in between fill ups.

 

 

+1

 

So far my trip computer has been 1-2 MPG off than what I calculate.

[Max Capacity]

The 99.9mpg is when the car is coasting. If you give it gas the mileage drops.

 

The reason it only reads 99.9 is because that's all the digits in the display.

You should be keeping your eye's on the road not reading some ever changing numbers on the dash.

[DriverX]

I have found the Avg MPG calculation to be rought 1 1/2 mpg too high as well. I use the B trip to take an average every 10,000 miles. Remarkably, every time it rolls over it's roughly the same MPG. It's been reading either 26.4 or 26.7 mpg each of the 5 times it's rolled over so I figure it's pretty safe to assume that I average about 25mpg in my mixed (not a lot of just highway) driving.

 

FWIW, I used the instant MPG feature during break-in....