mpg calculated vs computer

First fill up... Drove 414 miles.. Computer said 43.9 . Hand calculated 42.5. Weather 40-65 traveling about 50/50 freeway and city..

Just took approximately 130 mile trip from Fayetteville NC to Wilmington NC is about 45 degree weather. Most of traveling was a between 50-55mph. Averaged over 52mpg by the computer. Nothing unusual except conservative driving.

First fill-up for our v. 45.9mpg displayed by the computer; actual calculated--45.03mpg. Very, very happy with the mpg and with the accuracy of the trip computer.

2nd full tank ever
41.6 mpg-Displayed. 41 according to Fuelly.
2012 v Two
16" wheels 35psi front/35psi rear


Just upped cold pressure to 40 psi all around so we will see what happens...

Love it. Improved MPG by over 2mpg since first fuel up.

Second fill up, I drove 470 miles, the computer said 47.9, I put in 10.123 gallons which works out to 46.4 hand calculated.

I drive about 50% city, 50% highway, temperatures have been roughly 30-50 F. I have about 800 miles on the v now.

I log every fill and the computer is consistently 2 to 2.5 MPG higher than reality. Thus far, I have filled the tank 13 times and all but one have been at the same pump using the same process for filling.

Same here after 11 fillups.

However, it doesn't take much additional fuel to make the difference greater. On my last fillup, the displayed average mpg was 51.4 after driving 461 miles (I still had 2 fuel bars left). So... 461/51.4=8.97 gal. The pump stopped a around 9.2 gals which yields 50 mpg. I added another half a gallon to round the dollar amount. That dropped my actual mpg to 47.6.

It seems that the 2 mpg difference seems about it. You can make it better or worse depending on your fill up technique.

I reset the trip with every fill up, so far 3000 miles 46.8 on Fuelly (average) 49 on the trip meter. Every tank is consistantly 2.5 to 3.0 mpg off.

I always lean too far towards consipiracy but I find it interesting that my 2002 Toyota Sequoia has no such problem. Surely gas fuel gauge technology can't be that different.

I have not performed a comprehensive analysis of our new Prius V 2012, but I can tell you this: My wife is the sportier driver. I can get upper 40's mpg on a tank or single trip quite easily and typically get 50+ mpg commuting. However, my wife lives in the very low 40's mpg neighborhood.

I filled up this morning to the 'click' and still have the receipt. I also reset the Trip-B mileage to zero. I should be able to track computed v actual mpg next time I fill up (late next week!).

Is your wife interested in learning a more efficient way to drive your v? She may not realize there are different techniques. I didn't until I went looking. W

I'm pretty much convinced the Prius mpg indicator is inaccurate by design.

After 2990 miles, 50.3 mpg computer and 48.2 mpg calculated.

I am wondering if the gas stations gave the amount of gas stated? They could cheat by 2 or 3 percent and no one could have known.

I have noticed a difference of at least 1.5, and as much as 2, mpg in difference between what the gauge for a trip shows, and what the calculated mileage is. I have about 8000 miles on the car (purchased at the end of Jan in Minnesota). Obviously, getting MUCH better mileage in the warmer months than the cooler. I also am a conservative driver, although annoyingly so. LOL! My "lifetime" average to date is 50.1, so I figure that means around 48 actual. Can't complain about that!

Can you reset the life time average? I haven't try it yet but don't want to lose my life time average.

Here you go.

From the Owner's Manual
p199: While the odometer is being displayed, or when the odometer/trip meter are not displayed, the average fuel consumption from the last reset will be displayed.

p49: Selecting "Clear" on the "Past Record" screen will reset the past records and best fuel consumption.

I'm averaging 41.3 on the computer... Fuelly puts it at 38.5 right now. That's after 10k miles.

I don't have ready access to a "measured mile" so I don't know how accurate my speedometer is. However, have read of other owners checking their speedo calibration and reporting indicated speeds 1 - 2 mph greater than true. I can see a manufacturer doing this intentionally to help owners avoid speeding.

I can also see this same error carrying over to the car's computer mpg readings. Of course, a little extra software could be used to remove the induced speed error from the mpg computer calculations, but Marketing might have nixed that extra effort.

Just a thought.

I had a Garmin portable GPS in my 2008 Prius and the speed shown by the Prius was about 2 mph higher than the GPS unit when I was cruising at 65 mph. I believe the GPS is much more accurate. In addition, when I use google map to get the distance between two points. The trip distance shown by the Prii (08 Prius and 2012 Prius V) are always about 3 percent higher. I think this is part of the scheme by Auto Manufacturers to spike up their MPG. My wife's CR-V has the same problem.

Because the odometer is likely to be juiced. Your and my calculated MPGs might not be accurate either because we rely on the odometer to track the mileage.

Since the mileage computer is juice about 4%, and the odometer is juiced by about 3%, the total computer reading might be about 5% to 7% too optimistic.

We have nearly 80,000 miles on our 2010 Prius. The indicated mpg readout
has been off since day one, over reading. For the last 6,000 plus (trip A)
miles the gauge is over reading by about 2.4 mpg. If the gauge
indicated displays 55 mpg I alway take off 3 mpg and at 52 mpg
that would give me a true reading.

It would be nice if Toyota had a software fix to make it 99-100 %
accurate.

I have done the GPS speed trick and a couple radar, here is your current speed signs to slow down traffic in high speeding ticket zones. My wife's 06 Prius, my old 07 TCH and now the V3 all display 2mph over the true speed. This seems to begin about 25mph and continue up from there. Maybe below 25 it is just 1 mph. Guess I need to go check that now.