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Hello,

I drove to Los Angeles and back today in my new 2019 Cross trek [sic]. It is my first road trip and so wanted to report the mileage and see how it compares. My trip took me from the San Joaquin valley over the Grapevine on Hwy-99 and I5 and all the way to Huntington Beach, then back home. Lots of freeway driving, hill climbing, downhill, city traffic, freeway hyper speeds, freeway bumper-to-bumper for miles, air-con on maybe half the time, one passenger.

Here are my stats…

Total driving distance: 306.4 miles
Gallons of gas used: 8.135
MPG shown on my car’s screen: 41.9 mpg
Actual mpg using simple math: 37.66

The 37.6 is good, but why so different than my car’s computer?

Thanks.
 

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Normal, but not right. Just about everyone that has done a manual calculation reports that the dashboard mpg calculator is about 5-10% generous. I read on one of the forums that a Subaru dealer can adjust the mpg calculator plus or minus 5% if you request it.
 

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^ As SubaruBill said this is totally normal and totally not right. I appreciate Subaru striving to make more fuel efficient cars as that is how we keep the ICE around in a world of ever increasing EV popularity but this is wrong. A totally unnecessary scheme as IMO the whole Subaru line boasts pretty respectable actual MPG when you consider their capabilities.

That is good to hear that the dealership might be able to adjust that. I have always wondered if this discrepancy is limited to the MPG read out or if it also affects the estimated fuel range.
 

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We’ve discussed that several times over the past couple years and here’s what I’ve learned.

Cars base their fuel economy on the volume of air moving through the mass air flow sensor. It’s not perfect but gives a reasonable(?) approximation. The only accurate way would be to measure the actual gas consumption rate but that doesn’t seem practical as it introduces a new, single purpose component to physically fit along the gas line somewhere.

I suppose they could modify the fuel pump to measure how much fuel is passing through it. Then they’d have to put that data into the computer to spit out a number. However, I don’t think introducing new seals for the gas to deteriorate sounds like a good idea.

When fuel ratings are established, they do not use the onboard system to measure it. They measure the actual fuel consumption rate.

I can’t complain about it; my exaggerometer says I’m averaging 6.8L/100km but my real word to date is 8L/100km. However, the published city/hwy economy is 10.5/8.1L/100km. I’m getting better mileage than advertised!
 

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I am mystified that anyone would trust any of the guages to be totally accurate. The readout for miles per gallon usage is a most an approximation and In my 2014 XV Crosstrek has never ever even been close to the actual gas mileage that I track in a hand written log. Also the gasoline guage for capacity is never completely correct.

I would expect that the tire pressure and all other guages measuring anything on any current automobile to be just a guesses.
 

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I am mystified that anyone would trust any of the guages to be totally accurate. The readout for miles per gallon usage is a most an approximation and In my 2014 XV Crosstrek has never ever even been close to the actual gas mileage that I track in a hand written log. Also the gasoline guage for capacity is never completely correct.

I would expect that the tire pressure and all other guages measuring anything on any current automobile to be just a guesses.
You'd be surprised at how many new owners post here about the great mileage they are getting and it turns out they are only looking at the Exaggerometer...

I also find it suspicious that it's always 10-15% more optimistic. I don't recall anyone posting here that they are getting better mileage than what the car reports. That's why I think it's intentionally misleading, to the benefit of the car manufacturer (they all do it).
 

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You'd be surprised at how many new owners post here about the great mileage they are getting and it turns out they are only looking at the Exaggerometer...

I also find it suspicious that it's always 10-15% more optimistic. I don't recall anyone posting here that they are getting better mileage than what the car reports. That's why I think it's intentionally misleading, to the benefit of the car manufacturer (they all do it).
2032652, member: 241818"]
My fuel consumption reading is consistently 11% optimistic, no matter the type of driving. However, I'm still getting better than the published figures so I cannot complain. Fuelly does a good job for accurate l/100km readings
[/QUOTE]
Yes, my 2019 on board computer is optimistic. Cruise control helps greatly plus a mid range octane can't hurt.
 

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You'd be surprised at how many new owners post here about the great mileage they are getting and it turns out they are only looking at the Exaggerometer...

I also find it suspicious that it'a s always 10-15% more optimistic. I don't recall anyone posting here that they are getting better mileage than what the car reports. That's why I think it's intentionally misleading, to the benefit of the car manufacturer (they all do it).
2032652, member: 241818"]
My fuel consumption reading is consistently 11% optimistic, no matter the type of driving. However, I'm still getting better than the published figures so I cannot complain. Fuelly does a good job for accurate l/100km readings
[/QUOTE]
Yes, my 2019 on board computer is optimistic. Cruise control helps greatly plus a mid range octane can't hurt.
 
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