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Discussion Starter · #1 ·
I recently bought a 2000 Outback with a 5 speed, and the car has been running well and everything appears fine. I drive across the state for school and thought I'd calculate the gas mileage I was getting. After driving 187 miles on the highway I had to put almost 11 gallons of gas into it. that's just over 17 Miles per gallon! Has anyone else had this problem or know a possible cause for the mileage being this bad?
 

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Meh.
I has wagons.
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Not enough info.

In theory you should be getting 10MPG better than that. BUT, important details are missing.

-Speed?
-Cargo?
-Anything on roof?
-What type tire?
-What PSI?
-CEL on?
 

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Silver: 2009 Subaru Outback Limited Edition, 2.5 Liter EJ25, Automatic. Gem: 2002 Subaru Outback LL Bean Edition, 3.0 liter EZ30D, Automatic
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Are you using the recommended octane for your car?
 

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Discussion Starter · #4 ·
I was driving between 70 - 75 mph the whole trip. The only cargo was me and one passenger and there is nothing on the roof. The tires on the car are summer tires and have a lot of life left in them. the PSI in the tires is at 26, which is lower than the 29 recommended on the B pillar. The check engine light is not on but does work. I know this because I have accidentally stalled the car and it comes on and the code reads that the engine is running lean. Light turns off by itself after a few minutes however.
 

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2002 3.0 VDC Wag + 2018 2.5 Leg Ltd
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Are you using the recommended octane for your car?
2000 only come in plain old H4 2.5,...and they run on ordinary low octane.
I had a 2000 wagon though, 23mpg on 87, and 27mpg on 93.



but 17 mpg is pretty bad, like there is something wrong.

like tire pressure:

26 is way to low.

raise the tire pressure all around to 35psi. and recalculate. in my 2.5 sedan right now I get 29mpg. (35psi does not hurt the car or the tire.)
 

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Meh.
I has wagons.
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Tires should be at 30F/29R. I have mine at 35F/34R as my Continentals felt way too squishy at doorcard specs.

Something is wrong though, at 70MPH you should still be in the 25MPG range.

FWIW: Kaylee has broken 31MPG at 65MPH. With a bit of a tailwind... 17MPG is bad wrong.
 

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Silver: 2009 Subaru Outback Limited Edition, 2.5 Liter EJ25, Automatic. Gem: 2002 Subaru Outback LL Bean Edition, 3.0 liter EZ30D, Automatic
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FWIW: Kaylee has broken 31MPG at 65MPH. With a bit of a tailwind... 17MPG is bad wrong.
Can Kaylee still do that with the bad head gasket?
My gas mileage was pretty bad before having the head gasket repair.
Around 21-23 mpg, now seems to be better.
 

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Meh.
I has wagons.
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Can Kaylee still do that with the bad head gasket?
My gas mileage was pretty bad before having the head gasket repair.
Around 21-23 mpg, now seems to be better.
Haven't had her on long road trip in a while due to assorted issues, but MPG has dropped a bit. Not major but enough off her normal to notice though. Working my way through problem solving. Plugs and fuel filter so far. Next step brake hardware, might have a sticky caliper.
 
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2006 Outback 2.5i 4EAT
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I'll echo the other sentiments. I can cruise at 70 with mine (00, 5mt) and see upper 20s regularly. Something is not right.

-Specifically what code did you get that said it was running lean? Does the car have decent power, without any sort of hesitation or bucking?

-Can you check your spark plugs and see if they look normal? If the ends are brown or black, your engine is likely rich. If they are bright white, it could be lean. They should be a grey color.

-A lean code could be a few things (depending on what exactly the code is). You could have one of a variety of sensors reading badly like the front O2 sensor (AKA the Air/Fuel Sensor), MAP sensor, even a ECT (coolant temp) or Knock sensor. You could also have a clogged fuel filter. I would personally get a VAG-COM cable and download romraider and freessm to do some data logging. The cable isn't expensive and the software is free.

-I would also look into doing a compression test, if you have the ability. Auto Parts stores usually rent those testers for free and it is fairly easy to do, especially if you are already checking the spark plugs.
 

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Discussion Starter · #10 ·
Thanks for all the responses. The head gaskets, spark plugs and wires and brakes were replaced in the last 4000 miles. This was before my ownership of the car however. I have considered checking the plugs and compression but was looking for another possible cause since these have been replaced recently. There is the possibility that when the head gaskets were replaced the heads should have been milled and were not. The CEL only comes on if I stall the car but not every time. I'm not sure the exact code, but my reader said the engine was running lean. The light will turn itself off after a few minutes. I also considered a sticking caliper but the car will roll in neutral (driving or pushing) easily and does not make any ill brake noises while driving. There are also no signs of excessive/ uneven wear on the rotors or pads.
 

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Are you sure you calculated the number of gallons used close? A gallon or 2 would make a huge difference in your calculation. Perhaps your next tank will show over 30 MPG. It can be hard to put a known amount of gas in a tank...even when filling up after every tank.
 

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These calculations are definitely flawed.

Your running your tires way to low. As suggested, run at 32-35 PSI. You'll probably gain 3-4 mpg right there
 

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Discussion Starter · #13 ·
I wish I could say my calculations were flawed. I filled up my tank before I drove across the state and took a picture of the odometer at 217785. When I got home I again filled up the tank. I took a picture of the pump which reads 10.888 gallons, and again took a picture of the odometer now at 217972. That's 187 miles, which is the correct distance burning 10.888 gallons. which comes out to 17.1748 MPG. Though it shouldn't be (even with my low tires) that's unfortunately accurate. On my next trip I will certainly calculate my mileage again though
 

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There are still a lot of variables, the way you're calculating.
 

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'03 outback limited, '01 Outback Limited, '01 Legacy L wagon, '96 Legacy Brighton wagon
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You will get accurate fill numbers ONLY if you fill right up to the filler cap - relying on the auto-shutoff can leave you all over the place, depending on the GPM filling speed, which in turn affects the foaming of the fuel that shuts off the pump. I've seen as much as a 2 gallon difference from nozzel shutoff to topping the tank from one station to another, and even at the same station. My '96 legacy wagon usually varies at least 1/2 gallon, and sometimes closer to a full gallon.
 

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What state? That fillup 187 miles from home: was it the same fuel standards that you are used to? IOW, bad gas: E15? MTBE added? 85 octane like in Utah?
 

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2001 VDC Wagon - White pearl - 302,000 km
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You will get accurate fill numbers ONLY if you fill right up to the filler cap - relying on the auto-shutoff can leave you all over the place, depending on the GPM filling speed, which in turn affects the foaming of the fuel that shuts off the pump. I've seen as much as a 2 gallon difference from nozzel shutoff to topping the tank from one station to another, and even at the same station. My '96 legacy wagon usually varies at least 1/2 gallon, and sometimes closer to a full gallon.
DO NOT FILL TO THE FILLER CAP! You will super-saturate your evap canister and you'll end up with a CEL that won't go away quickly.
The only way to be sure is to fill up each time at the same station, using the same pump each time.
 

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Discussion Starter · #18 ·
Today I drove back across the state so I filled up at home. Home and school are both in Michigan. Ended up with the same 17 MPG. cruise control on 70 the whole way. I tested the compression, and all four cylinders are between 180 and 185 psi which is good. The air filter is plenty clean. the brakes are not causing the problem, I've checked that. The head gaskets, plugs and wires have been changed in the last 4k miles. I checked the plugs and they are not black or white. So the car shouldn't be running rich or lean. And all the fluids are to the correct levels. I don't know where to look next. I'm beginning to wonder if the car is leaking gas as I drive. Doesn't leak anything while parked however. Also, this is my first Subaru and while in 5th gear doing 70 mph the RPM's are running 3,500. This seems unusually high to me, I was wondering if this could be part of my part of my problem.
 

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Meh.
I has wagons.
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Something is still wrong. That MPG is worse than I got in rush hour traffic.
 

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Something is very wrong. An MT should give you great mileage since there is no parasitic loss from a torque converter. I have never owned a Sube MT, but my other 4-banger MTs all ran higher at highway speeds. Consider how little torque there is in a 2.something liter engine. Basically, horsepower is what is needed to push the car through the wall of wind resistance. V6s and V8s are usually geared much differently since all that torque is on tap to do the pushing.
 
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