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Old 09-26-2012, 04:39 PM   #1
hozouria
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Default incorrect mpg readings, or mechanical issue?

I know these MPG related posts are dime a dozen, but I genuinely did try to look through what other posts have been made to see if my question had been answered. I didn't have any luck, but in case I missed it, please forgive me! Don't wanna upset any of you guys (or gals)..

Anyways, I'm having a little trouble with my '12 wrx. First off, I know this is the wrong car to complain about fuel economy, so I'm not desperate to get 400+ miles/tank, but I'd like to get at least close to what's advertised, which I hope isn't a crime.

Currently, I drive about 75% easy highway, 25% city/slightly "delayed" shifts. During normal driving, I try shifting between 2800 and 3k rpm, except on 5th which I can usually get snug into while coasting ~45 on the flats (rpm usually sinks to around 1600 here). During aforementioned "delayed" shifting bouts, I don't let it go past 35/3700 rpm. So really hardly nothing more. After my perusing through the other posts, I've found some tips and techniques to try and get my city driving under wraps, but I'm still not getting the numbers I should be for the highway.

I recently went for a short trip with my gf. It was nice and relaxed, no hills or mountains. Once on the highway, I reset one of the mpg computers and it shows that I averaged about 26mpg, which I definitely will not complain about - I was stoked. But the problem was, I wasn't getting that in truth. I did the calculation on paper and really only got 21ish. This was driving pure highway at 66-69, keeping revs at 2600. I wasn't lugging anything heavy around, and have always been using 91 octane. We had the A/C on intermittently, but I was being pretty conservative on the highway (the police are crazy here), so that shouldn't have affected this severely. Not to mention, give me inaccurate readings. I really don't know where I went wrong.

At the end of this last tank (used for our trip), I finished at 330 miles when the light came on. Which isn't shabby, really. But considering I did 95% highway on that tank, I'm confused. Do I have to wait longer in the break in period until I see some happier numbers?

Thanks all, and again, my upfront apologies if this is a repeat post.
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Old 09-26-2012, 05:12 PM   #2
bacalhau16
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The mpg calculator/display in the car is definitely generous. You will notice that it is always higher. 21 mpg is pretty average. Perhaps a bit low for the highway, but not terrible.

Your rpm isn't as much as your making it. You could be driving under heavy throttle to 3500rpm and that wouldn't benefit you.

Ensure that your tires are inflated properly and alignment is in order. You should see better mpg eventually, but I wouldn't expect a lot more then 23-24mpg
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Old 09-26-2012, 05:17 PM   #3
GravityDefyingSTI
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I don't have an answer for you but I wish I could get 330 miles from a full tank lol. If I get 280 I'm happy sometimes. So maybe you'll feel a little better knowing there's other people out there (like myself) getting way less then you are. I was talking about it with some co workers yesterday and I told them in the end you can't own this car and be mad that you only get xxx amount of miles per tank, if you are get another car lol. I'm not saying that to you though, I see your point, but as for me I DRIVE my car, I have fun with it and sometimes I feel like I see the fuel gauge dropping before my eyes!
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Old 09-26-2012, 05:31 PM   #4
ChesterWRX
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um yeah,

i drive pretty much like an old lady. i take off slow, feather the clutch between 800-1200 rpm from a stop and shift at 2500 rpms (give or take).

my MPGs are about the same as your readings so i'm guessing i'm getting between 19-22 avg mpg since my computers are reading 22.5 and 23.1 as of today. the lower number (trip a) has about 500 miles since installing the Cobb AP Stage 1 MT 93 v300 and trip b has about 1800 miles.

i have 3300 miles on it total.

one thing i noticed is driving like an old lady keeping off the WOTs keeps you out of boost... i had my Cobb AP on and never went into boost.

i wish the WRX's had the fuel economy guages like the legacy. i like monitoring it for ****s and giggles.

on the highway, i got similar readings (26+ avg mpg) so i figured i'm doing ok for 65-75mph and running 93 octane.
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Old 09-26-2012, 05:34 PM   #5
ChesterWRX
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ETA: ROFL, i'm not overly concerned about the fuel economy. it still beats my old Magnum R/T by almost 10mpg city.
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Old 09-26-2012, 05:39 PM   #6
guroove
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Quote:
Originally Posted by GravityDefyingSTI View Post
I have fun with it and sometimes I feel like I see the fuel gauge dropping before my eyes!
I'm pretty sure that you actually can see the gauge drop during a long WOT pull on the highway.

To the OP, I've only gotten over 330 miles on a tank once, and it was lots of side road driving, very little highway, most of the tank was 45 - 55 mph.
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Old 09-26-2012, 06:34 PM   #7
hozouria
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Okay, I guess this is just what it is. I optimistically had this idea in my head where if I actually drove gentle highway miles with cruise control I'd get 25mpg all the way through, ending in at least 350 per tank. My usual commute won't be so highway friendly. I think last time I went through a full tank during a week or so of normal commutes I averaged 20.7 mpg, lasting 290 miles. I'm looking through these other mpg-related posts and people are getting 28+mpg somehow, and can finish a tank off in 350 miles or more with ease. That said I'm not gonna cry bc I bought a guzzler and expected a hybrid, but I'd like to get close to published numbers! Besides, sometimes just driving as carefully as I can for mentioned sh**s and giggles can be fun too.

I also see some people have put K&N filters in their cars? Is this a breach of warranty or a good idea to try?
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Old 09-26-2012, 10:31 PM   #8
Dragonfueled
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Don't feel bad my commute is about 4.5 miles each way in traffic to work 09 wrx stage 2.In the winter months I average 14-15 mpg lol. It still lasts like two weeks on a tank but damn city driving kills the miliage on these cars. Same commute my integra gets 22 mpg lol but it's got 200 less horse power

Easy highway driving I'm rite in the 21-23 range.
I'm guessing the new gen wrx will get much better miliage and direct injection but wow our cars respond great to mods.
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Old 09-27-2012, 12:28 AM   #9
MtnXfreeride
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When my 2012 wrx was 100% stock I was getting 23 mpg according to the computer.. and 24mpg when I switched to a K&N drop-in filter. (surprising since I was getting addicted to the louder swoosh of air being sucked in)

I am now stage 1 with the stock air filter (it was causing knock with the Access port) and average 21mpg with daily "spirited" driving on my commute. When I fill up I calculate actual mileage because I dont think the car computes for the gas on engine startup.. usually it is 0.5mpg less.

On occasion Ive noticed my car clicking full when gassing up and it not really being full.. and I can put another gallon in before it clicks again.. (you get an idea of how many gallons it should take to fill) I think the bubbling from gas can trigger the sensor early. So keep that in mind on your manual calculations.

These cars do best at 45-55mph in my opinion.. I can average 26mpg on long backroads at that speed.
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Old 09-27-2012, 12:55 AM   #10
garudatwo
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Mudflaps, roof racks, fat chicks, fat bros will all decrease your MPG FYI.
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Old 09-27-2012, 04:53 PM   #11
BbugWag
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Well my .02 on this. My STI gets 25-26 mpg on back roads. Significantly less highway driving. I noticed I get the best mpg between 55-60 mph. On the highway I'm normally upwards of 65 which would result the mpg loss but my mpg calculator on the car is always wrong when I do the math at the pump.
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Old 10-01-2012, 11:56 AM   #12
hozouria
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thanks BbigWag. I noticed that if I drop my highway speed to about 60 (from 69), my revs drop from 2600 to nearly 2000. over a couple miles I could definitely notice an improvement in gas mileage. I guess that's just what it takes.
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Old 10-01-2012, 04:28 PM   #13
Source,LLC
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21 sounds about right to me. I average abuot 17.5-18 with 60/40 highway/city driving on E85, but it's worth every bit of extra torque lol. Honestly a better flowing exhaust would help you increase gas milage (less back pressure), but then you'd need a tune and more boost usually means more right foot
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Old 10-10-2012, 04:44 PM   #14
hozouria
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Quote:
Originally Posted by Source,LLC View Post
21 sounds about right to me. I average abuot 17.5-18 with 60/40 highway/city driving on E85, but it's worth every bit of extra torque lol. Honestly a better flowing exhaust would help you increase gas milage (less back pressure), but then you'd need a tune and more boost usually means more right foot
You use E85?? Won't that kill the engine? I have been pondering a better flowing exhaust, but that's a hefty investment, and I'd rather start with something like fine tuning my driving technique and maybe a K&N filter, etc. There are so many exhaust options too. I have no clue where I'd start. sheesh.
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