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Old 04-18-2018, 12:06 PM   #1
BlueBellThunder
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Default Gas mileage

Think I may have been cheating on gas. According to the car I got 25 mpg. When I filled it up it was 23. I reset the trip meter after my first fill up. It took 15.3 gallons. If I’m not mistaken the capacity is 15.9. The car said I was 10 miles to empty. I know some cars have a up to a 2 gallon reserve. My question is do these have less? My first fill up 10 days ago at the same station different pump was 13.5 gallons and the car had 50 miles to empty. It’s a Sunoco station, I’ve never used them before, always went to wawa and got regular. Wawa’s regular is 92. I’m assuming that’s god enough, but they actually charge more. But if this Sunoco is cheating me, I’ll look elsewhere. This is a new car and only my second fill up, it’s a 2018 WRX CVT.

Thanks for letting me rant.
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Old 04-18-2018, 01:02 PM   #2
Commander Keen
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Highly unlikely you're being cheated.

Miles to empty on any car is a rough estimate, pessimistic by design and shouldn't be relied upon.

Also, gallons to full can vary based on the incline of the ground you're fueling on.

I believe gas stations are subject to random testing by most states and fined heavily if found to be cheating. If you really want to know the truth, fill a container you can later inspect.
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Old 04-18-2018, 02:29 PM   #3
BlueBellThunder
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I forgot to mention I live in NJ, were sometimes gas stations get caught, we are probably higher than the national average. Not that you see this on the news on a regular occurrence. I’ll have to read the manual, to see if this car has a small reserve.
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Old 04-18-2018, 03:40 PM   #4
Commander Keen
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There is no discrete "reserve", just a single tank.

Letting the fuel get that low is a bad idea for a number of reasons.

Quote:
I forgot to mention I live in NJ, were sometimes gas stations get caught, we are probably higher than the national average.
Your state is the only one which prevents you from operating the pump. Odd coincidence.

Last edited by Commander Keen; 04-18-2018 at 03:46 PM.
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Old 04-22-2018, 07:29 PM   #5
EricP350
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87 octane is all you need, any more is pouring good money down the drain. Higher octane provides no benefits in modern computer controlled vehicles.
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Old 05-12-2018, 08:31 PM   #6
BlueBellThunder
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Quote:
Originally Posted by EricP350 View Post
87 octane is all you need, any more is pouring good money down the drain. Higher octane provides no benefits in modern computer controlled vehicles.
The owners manual on the 2018 WRX says it’s mandatory to put at least 91 in the car.
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Old 05-14-2018, 07:17 PM   #7
BlueBellThunder
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I got gas again today at a different station same result, car says I got 24.3 mpg, but the miles I drove and the amount of gas it took says I got 22.3 mpg. The chances of 2 gas stations being shifty are unlikely. So I guess the cars computer isn't accurate. No big deal, if I was being cheated, now that would be a big deal.
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Old 05-14-2018, 07:24 PM   #8
DieselDorf
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I've heard a few people mention the cars computer is off based on hand calculations as well, mine included. Not by much though
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Old 05-15-2018, 12:53 PM   #9
Harriska2
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Quote:
Originally Posted by Commander Keen View Post
Your state is the only one which prevents you from operating the pump. Odd coincidence.
Oregon is another state. My gas mileage based on gallons to fill up and miles driven have been stable since after the first 4 or 6,000 miles on our 2017 impreza.
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Old 06-04-2018, 12:33 AM   #10
joshrfrank
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Quote:
Originally Posted by BlueBellThunder View Post
I got gas again today at a different station same result, car says I got 24.3 mpg, but the miles I drove and the amount of gas it took says I got 22.3 mpg. The chances of 2 gas stations being shifty are unlikely. So I guess the cars computer isn’t accurate. No big deal, if I was being cheated, now that would be a big deal.


It also depends on how you are driving. I also have a 2018 WRX and when I drive easy, I get like 28 mpg but once I run it hard, that’s when it drops to like 23 mpg.
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Old 06-04-2018, 12:55 PM   #11
Scooby Coupe
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Quote:
Originally Posted by DieselDorf View Post
I've heard a few people mention the cars computer is off...
Yeah, mine is consistently over-stated by 2.0 - 2.5 mpg. Not an issue for me, though.
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Old 06-04-2018, 07:56 PM   #12
DaSubie22
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Default Gas Mileage

I have a '15 WRX mt stock and my calculated MPGs are always 1.5-2.5 mpg lower than the computer. I have noticed when my driving is "less spirited" it's on the lower side 1.5 off and more aggressive driving seems to make the difference bigger.
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Old 06-04-2018, 08:01 PM   #13
DaSubie22
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Default Gas Mileage

Quote:
Originally Posted by joshrfrank View Post
It also depends on how you are driving. I also have a 2018 WRX and when I drive easy, I get like 28 mpg but once I run it hard, that’s when it drops to like 23 mpg.
Not to burst your bubble or anything, but I think if you do a manual calculation of your fuel, you will notice you are not getting that great of gas mileage. I reset trip B at each fill up (trip A I use for oil changes) and when I go to fill up again, I divide the miles by the gallons of gas put in. That mpg is always lower than what the computer says. I just drove like a grandma and got 24.9 mpgs (manually calculated). My computer said 26.7 mpg.
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Old 06-20-2018, 02:36 AM   #14
Azsubi
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Quote:
Originally Posted by BlueBellThunder View Post
The owners manual on the 2018 WRX says it’s mandatory to put at least 91 in the car.
I wouldn't put anything under 91
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Old 07-15-2018, 03:56 PM   #15
quidnatch
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Quote:
Originally Posted by EricP350 View Post
87 octane is all you need, any more is pouring good money down the drain. Higher octane provides no benefits in modern computer controlled vehicles.
Not true. While modern cars will retard timing to adjust for lower octane it will reduce the power output by doing so. On most cars its not a big deal, maybe a few up, and people won't notice. However, in turbo cars like the WRX, GTI, etc it can be as much as a 20hp loss. Go to Mazdas website and look at the 2018 Mazda 6. It shows different numbers for 87 and 91

FYI. I work in the industry and can say 100% that all car testing for MPG, Up, etc is done on higher octane gas. Even if it only calls for 87.
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Old 07-15-2018, 03:59 PM   #16
quidnatch
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The mileage calculator on this car is optomistic and thats being polite. To say it lies is more accurate. In order to determine your MPG you must do it manually. Use something like fuelly if you would like to keep a record.

I show 25.7 lifetime and usually get the computer to read about 29 per tank on my new commute. I am lucky to get 25 irl when calculating manually.
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Old 07-16-2018, 11:13 AM   #17
lymphomaniac
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The MPG meter (or here in Canada, the fuel consumption meter) is normally generous by about 10%. I had it happen with my 2013 Impreza, and it's doing the same with my 2018 WRX. I hear you can get it re-dialed by the techs to something more representative of real life conditions, but ymmv (pun intended).
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Old 07-29-2018, 01:38 PM   #18
WRX04Devotion
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The only reliable way how to calculate mileage is manually, like others say here. On my daily commuter I do it like this:

• When I arrive at gas station, I write down (or take a photo) of the fuel gauge, estimated remaining miles on current tank and the number of actual driven miles in trip meter since last gas station stop.
• Then I get X gallons of petrol which I can get for 40$ and also keep the bill, where the exact amount of petrol is printed.
• Before I leave gas station, I reset the trip meter.
• At home I shovel all these numbers in spreadsheet, which calculates MPG (from traveled distance / purchased petrol from previous gas station visit) and tracks petrol price. I know, there are some apps for it, but I like to set up my own charts, where I can eventually extrapolate even more data.
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