How accurate is the MPG gauge?

[Heavishot]

4 fill-ups so far computer is .1 - .75 better mileage than reality.

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[Madman]

4 fill-ups so far computer is .1 - .75 better mileage than reality.

@Heavishot -

That is my experience as well, but typically shows it is 0.3-0.7 mpg better than calculated, or around 2%.

As an aside, I figure that getting modestly larger tires (perhaps 33.5-34.0”) will balance at least some of this error out, as computer counts ‘wheel rotations’, not actual distance traveled, in calculating mpg.

At least, that’s part of my rationalization for buying bigger tires. ?

 

[UGADawg96]

When I still had the Hankook OEM tires, the truck was off about 1 mph. Since upgrading to 34" tires, it is now dead accurate. I haven't tried hand calc vs computer calc for mpg since I've only put gas in it twice and just hit 1300 miles. But I would assume the computer mpg calc is factored by speed and distance traveled.

 

[Jus Cruisin]

I don't even bother to check. I stopped hand calculating years ago. They are knick named LOM for a reason. I do see it all the time because that's what I have in the center of the IP. I use it as a gauge of what the engine is doing. Any strange differences will alert me to a potential problem.

 

[UGADawg96]

I don't even bother to check. I stopped hand calculating years ago. They are knick named LOM for a reason. I do see it all the time because that's what I have in the center of the IP. I use it as a gauge of what the engine is doing. Any strange differences will alert me to a potential problem.

Yeah, I tracked the first few tanks on our Outback when we got it ten years ago. I don't think I've ever rechecked it since.

 

[herothedog]

I think when running in generator mode or remote startup the fuel burned is not accounted for in the computer mpg? Does anyone know?

Since it has been sub-freezing temps the last month I have been using remote start to warm up and top off the battery. Hand calculation of mpg on my latest fillup on Friday was 5 mpg less than the computer.

 

[F-150 Prius]

15,000 miles, +/- 1 mpg
more important is DTE, which is accurate to about half a gallon … when the gauge shows "1" mile to empty, you've got maybe half a gallon in the tank Call or a 10 mile reserve or in other words, the most I've ever poured in is just over 30 gallons.

 

[2mileshigh]

I kept up on 5 different fill ups. I wrote down what the truck said I got, gallons used and miles driven. I then averaged out all the data collected over the 5 fill ups.

1. Total miles driven= 1,037.7
2. Total gallons purchased=53.02
3. Average MPGs from 5 events estimated by truck=20.74
4. Average MPGs calculated manually and calculator= 20.06

Difference from manual calculations and truck calculations= +0.68 MPGs higher with the truck numbers.

The the truck system was just a hair over 1/2 MPG higher than actual manual calculations. I did have one fill up that was off more than the other 4 by twice what the others were. You throw that one out and only use the other 4 the difference is even less than +0.68. It would have been +0.3

Think I am just fine with relaying on the truck numbers!

I also did this on my 2018 Eco Boost and got very similar numbers.

I'm on tank 5. Through 4 tanks the difference for me was +.36 MPG higher on the truck's numbers. Close enough that I'm not going to bother with hand calcs any longer.

 

[ZOSICK]

15,000 miles, +/- 1 mpg
more important is DTE, which is accurate to about half a gallon … when the gauge shows "1" mile to empty, you've got maybe half a gallon in the tank Call or a 10 mile reserve or in other words, the most I've ever poured in is just over 30 gallons.

That's good to know for sure. I've seen a few videos out there and some say the gauge reads 1-2 mpg high and some say they read low. I'm curious how the measurement is actually calculated. I've also read on here that the distance to empty is off up to 5 gallons. Pretty crazy seeing as some see over 600 miles on a take.

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