Dashboard MPG vs. Driver calculated MPG by the tank - Club Crosstrek | Subaru XV Crosstrek Forums
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Old 11-22-2017, 05:42 AM   #1
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Angry Dashboard MPG vs. Driver calculated MPG by the tank

Bought my 2018 Crosstrek in August and was pleasantly surprised at the great gas mileage (around 32/33 MPG) as shown on the car's dashboard. I decided to check the numbers by calculating it the old way (if you drive 300 miles on a tank of gas and it takes 10 gallons to fill it back up, you got 30 MPG). Gosh, the two numbers are WAY off! And, unfortunately, the dashboard #'s are always higher, sometimes by 2 or 3 MPG, once almost 4 MPG. I have about 2,000 miles on the car and have been doing these calculations on the last 3 or 4 tank fills.

Does anyone else do this comparison? Does anyone know how the car dash is calculating MPG?

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Old 11-22-2017, 08:42 PM   #2
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There was an old recall on Honda fits for this Very issue. It would not surprise me if SOA screwed up and did this on their cars. It would be a court matter in terms of warranty and stated miles per gallon.
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Old 11-23-2017, 12:50 AM   #3
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It almost always reads optimistic. It's just normal.

Only once did it read lower than actual.

That was when I hypermiled my Subaru XV Crosstrek with Yokohama Geolandar A/T-S all-terrain tires.

I got 40.2 MPG average that tank, it showed something like 39.7 MPG.
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Old 11-23-2017, 12:26 PM   #4
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Yes, your observations seem pretty typical. I track my gas consumption through one of the gas websites as I do a lot of daily freeway driving and often try to drive gently enough to keep the dashboard reading above 33. My overall average for the year by actual measured stats on the website reports my overall average for 2017 is at 30.04 currently. Still, that's not a bad average for all types of driving but it seems we must take the dashboard readout as a relative indicator at best.
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Old 11-24-2017, 05:27 AM   #5
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How do you calculate MPG from a website?!

I've read more about fuel gauge methods. Edmunds car group did some testing, and yes, they found car fuel gauges are always too optimistic. The car calculates MPG by sensing what the fuel injectors emit. I simplistically assumed the gauge measures the gas left in the tank. They should really adjust their #'s downward, it's darn misleading.
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Old 11-24-2017, 09:35 AM   #6
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Quote:
Originally Posted by dhsieh View Post
How do you calculate MPG from a website?!
The one I use is my local edition of the gasprices.com (aka GasBuddy) site and there are also others that I've seen mentioned in these forums but can't recall any names right now. This site has a feature called Fuel Logbook where you can track your fuel spending over time. Of course, it only works as well as the data you enter into it.

You just log each gas fill with the date, price paid, the quantity, and odometer reading. The site keeps a record for you and calculates the MPG based on your input. You can compare multiple vehicles, and even see bar graphs of your total spending and overall fuel economy month by month, tracking trends. It can give you a pretty good picture of your usage, but again only as good as your data you feed into it.

Here for example is my current Crosstrek MPG chart for the year so far:
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Old 05-16-2018, 03:37 AM   #7
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Have an 18 Crosstrek that I bought in August 17. Computer shows 25.5 or so mpg. In the winter, it was reading 17.7 mpg, live in PA. Now in the 70's for highs, I did the old method, the computer on the Crosstrek said almost 26 mpg with this tank of gas, and when I checked it, it was 23.78. So I believe there might be something wrong with it, but the engine feels fine. Everybody I talk to are getting 28 mpg or higher, and some of them even changed their tires to something more aggressive. Mine is stock, CVT Limited model. Need to have the dealer check it out.
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Old 05-16-2018, 03:13 PM   #8
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Ive got over 11,000 miles on my 2018.

The computer readout is CONSTANTLY 2-3 MPG HIGHER than the real world numbers (miles driven divided by gallons pumped).

Im averaging 24/25 MPG real world. Computer always reads 27-28.

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Old 05-16-2018, 07:59 PM   #9
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Thanks for the data, MN Moose! Good info.
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Old 05-17-2018, 11:41 AM   #10
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Thanks for the information. I thought maybe there was something wrong with my Crosstrek. I have an 8 minute drive to work over a small mountain. About 70% is highway speeds, surprised about mileage since the engine only has 152 hp. My Crosstrek has about 8,300 miles on it.
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