My Legacy GT V8!

[Scotty]

CA91 winter gas results in about <1 mpg difference for me and it's a 5EAT. I do a daily 150 mile commute that goes from 50' elevation up to 2700' and back. It's about 100 miles of highway and 50 miles of 2 lane montain roads still at highway speeds. Summer time I was filling up @ 300 miles around 12.5 gals, now it is at 12.8 gals. There's also a 50+ degree temperature change.

[LemoineGT]

Any volume of air forced (or drafted) through an engine at a low temperature will require more fuel than would be required of the same denisty of hot air. Even once the engine is warm. You are correct in saying there is a cold start enrichment, and open loop mode -- as well as there being coolant temperature correction factors for both open and closed loop....

 

Look at a normally aspirated engines coolant tables, cold start tables, and air intake temp tables... And figure out percentage of injector pulse width... per arbitrary value... and you'll find that air intake temperature has a higher correction curve than the coolant temp table.

 

It's all relative, but most BOSCH and MOTOROLA fuel injection systems weight air temperature more than coolant temp for open loop injection pulsewidth. There are several other things which can and do occur -- i'm focusing on things that will happen in suburbia, such as stop and go driving, which can bring the car in and out of closed loop mode. all the stops and starts can easily do that.

 

--Lee

[derffred]

that's a very good point, but you have to remember the three things that determine closed loop is Time, Temperature, and O2.

[robinlsb]

Have you tried looking for a gas leak. The subie engine box prevents you from seeing anything. Try the smell test. Warm up the car, race the engine, shut it off and SMELL! OR look under the car. A small leak can turn into lousy gas mileage , but not always a fire

[avengador1]

I have a 5EAT LGT and I drive a relatively short 14.5 miles to work everyday. I also have a lead foot, but I still get around 20 MPGs for the week during the Winter. I don't go by the on board calcualtion for MPG, although it is usually close to what I calculate. I just top off and divide the weekly mileage by the gallons to top off again. My mileage had gone down recently by 2 MPGs and I found one of my tires had a slow leak and was pretty low. Once this was fixed my mileage went back up to what it normally runs. During the Summer I average 22 MPGs for the same trip to work. The best I have ever gotten out of my car is 26 MPGs on a 4 hour long highway trip. The lowest I ever got was 14 MPGs of all town driving.

[MangoGT]

How about this for a solution - check the tire pressures. Try bumping them up to 35 psi front and 33 psi rear. Maybe it is just your driving with your tires underinflated.

 

Thanks. That's been covered about 400 times already. If it is either my tire pressure or my driving style, then why did the dealership test only come up with 16.8mpg with half highway/half city?

[MangoGT]

I have a 5EAT LGT and I drive a relatively short 14.5 miles to work everyday. I also have a lead foot, but I still get around 20 MPGs for the week during the Winter. I don't go by the on board calcualtion for MPG, although it is usually close to what I calculate. I just top off and divide the weekly mileage by the gallons to top off again. My mileage had gone down recently by 2 MPGs and I found one of my tires had a slow leak and was pretty low. Once this was fixed my mileage went back up to what it normally runs. During the Summer I average 22 MPGs for the same trip to work. The best I have ever gotten out of my car is 26 MPGs on a 4 hour long highway trip. The lowest I ever got was 14 MPGs of all town driving.

 

This is exactly what I'm talking about...

 

I make sure that I don't spool the turbo (i.e., let the 5EAT shift around 2-2.5k RPM), I don't have a lead foot, and I maintain my tire pressure. We're both driving in winter conditions and we both have a short daily commute.

 

Why is it that my fuel efficiency is so poor relative to yours? Subaru better find out soon...

[voyetra8]

Just an update:

 

Dropped the car off for service today, and as expected, got the "We hooked it up to the CPU, and it's not showing any codes. The EPA calculates mileage based on driving during ideal weather, at the speed limit blah blah blah it's within normal range."

 

So, the next step is to contact SOA.

 

Now, I had predicted this, so during the service, I asked them to switch to synthetic, to see if it would make a difference, and on the 30 mile ride home, I got an indicated 27.7MPG on the highway. :O

 

I also picked up a new air filter from the parts counter, and dropped it in when I got home. I'll report back with my results over the week....

[MangoGT]

Just an update:

 

Dropped the car off for service today, and as expected, got the "We hooked it up to the CPU, and it's not showing any codes. The EPA calculates mileage based on driving during ideal weather, at the speed limit blah blah blah it's within normal range."

 

So, the next step is to contact SOA.

 

Now, I had predicted this, so during the service, I asked them to switch to synthetic, to see if it would make a difference, and on the 30 mile ride home, I got an indicated 27.7MPG on the highway. :O

 

I also picked up a new air filter from the parts counter, and dropped it in when I got home. I'll report back with my results over the week....

 

I thought air filters were covered under warranty by SoA? If so, you should send them the bill!

 

PM me and I can give you the names of the people that I've been working with at SoA. Well, I should say the people that I've been trying to work with, since the "senior rep" won't return any of my phone calls! (which are just replies to the message he left on my voicemail last week asking me to call him back)

[Mach V Dan]

Why is it that my fuel efficiency is so poor relative to yours? Subaru better find out soon...

 

What car did you drive before? Normally the only thing that will give you consistently bad gas mileage is a shot front oxygen sensor, and these days the car will tell you about that (through a Check Engine Light). But I don't think your mileage is all that unusual. As mentioned above, city driving can make for pretty poor numbers. Winter formula gas makes it worse.

 

Plus, driving the car COLD makes it WAY worse. If your commute is short, say just 3-5 miles, the car will barely have any time to warm up. The car is going to enrich the mixture a ton during that time to make sure it doesn't stall. For people with 20-mile commutes, this is minor, but if your commute is very short, I can easily see this destroying your mileage.

 

Check your freeway mileage. I get about 22.8 (the optimistic estimate from the onboard computer) on my 20-mile mostly highway commute. Best I ever got was around 26 mpg from a 400-mile 50-55 mph trip. Worse I've seen is under 19 from a mostly highway tank with some city driving, and that was not during the winter. And remember, I'm using the computer, which is about 1 mpg high, in my experience.

 

I'd say your car is normal. It's winter. It's a turbo. It's AWD. That's how it goes.

 

--Dan

Mach V

FastWRX.com

[RockyMtnGT]

So I bought this new Lotus Exige and, ...well I love it and all, but dammit there is like no trunk space at all!!! How could this be?? WTF!???

 

I'm gonna bring it in to have it checked out...

 

Jk man, glad it's better for you. I get anything from 18 to 23 mpg. Never seen it down around 14mpg even after ripping the car all the way up to 11000 feet!

[MangoGT]

I took a 300 mile (roundtrip) highway trip over the weekend--I don't have the receipt in front of me but I'm pretty certain it was right around 320 miles one the tank. That means I averaged 21.3mpg on a highway only trip. That's definitely an improvement, but a big drop compared to my 24mpg on the same trip around Christmas.

 

I just finished speaking with the "senior rep" at Subaru and he said that he spoke with the dealership about the problem. The dealership told him that there is nothing wrong with the vehicle, and thus, he can't recommend any repairs to be performed. I mentioned that the PA Lemon Law states that after three visits to the dealership I'm eligible to make a claim. He said that he can't advise me on that but he doesn't think that my situation is a lemon law case.

[MangoGT]

Just an FYI:

 

Shell V-Power (only 92 octane in IL) definitely improved my mileage. Not by a lot, but when I'm getting 13-14mpg, an increase of 1 mpg helps.

 

I tried BP Ultimate and the difference is hugely noticeable. It's terrible!

[castor]

I have 3 in laws who work for Shell as Terminal Operators....the pipeline guys.

 

Anyway, up here at least Shell owns and runs the pipelines....all the gas is the same when it arrives and then each different company adds it's own additive package to each particular grade...Reg, Mid, Super etc. I did a tour of a large distrubution area and saw the additive tanks all marked, Perto Canada, Sunoco, Shell, etc.

 

My 3 in laws all told me that Shell actually loses money on their 91 Oct V Power additive package....but they make it up with Reg etc sales.

 

So I alternate sometimes with Vpower and Ultra 94.

 

I dont notice any difference.

[subarulez]

I know very little about cars but sometimes even noobs get lucky. Have you tried any fuel cleaners like STP? Other tip would be to try full synthetic oil. I have heard full synthetics can increase fuel efficiency. Just make sure it's mobil and a full synthetic not a blend.

http://www.mobiloil.com/USA-English/MotorOil/Synthetics/Myths.aspx

[LemoineGT]

I'm just curious... you've checked the differential fluids and things? I remember a thread about some cars having a loose plug on the rear diff -- mine was slightly loose but there was hardly any seepage (i checked this when the car had a whole 25.7 miles on it when i got it home!). I'm also concerned about any sort of irregular tread wear or perhaps an alignment / low tire pressure... or something similar to that, which would cause an increased friction drag on the drivetrain.

 

In the city and around town over here, i average 290 miles per tank. On the highway i've seen 340.

[team23jordan]

my legacy sounds like V8 when my cutout is open

[what]

wow.. I cant believe yall are getting that gas mileage with a new Legacy GT?? is that right?? I literally hall a** pretty much everywhere I go. And the lowest I ever averaged gas mileage wise is like 19 something. I even tested my gas mileage drag racing one night, I made about 6 or seven passes at a quarter mile track and averaged like 11 something.. so that was my worse gas mileage.. but I was drag racing..

[team23jordan]

i get avg of 21.2mpg-23.8mpg

[toogrumpy]

What?

 

What kinda times were you getting in the quarter mile? and to keep the thread on track I get 19-20 MPG on average, but I will say the cars computer is not all that accurate, you should check it with a calculator.

[MangoGT]

I'm just curious... you've checked the differential fluids and things? I remember a thread about some cars having a loose plug on the rear diff -- mine was slightly loose but there was hardly any seepage (i checked this when the car had a whole 25.7 miles on it when i got it home!). I'm also concerned about any sort of irregular tread wear or perhaps an alignment / low tire pressure... or something similar to that, which would cause an increased friction drag on the drivetrain.

 

In the city and around town over here, i average 290 miles per tank. On the highway i've seen 340.

 

I've had the tires rotated and I maintain my tire pressure pretty conscientiously. I'm going to wait until the summer--if the problem doesn't improve, then litigation (lemon law) here I come.

[Guest]

Hey, was your problem ever resolved?

[rony]

Hey, was your problem ever resolved?

 

Is it a problem?

[NewLegGT67]

I think 12-14 MPG should cause concern. But I have to agree with MikeBrave. I get better MPG at 80 mph 5th than 65 mph in 5th gear. If you hit the long two-lane highways (w/triffic lights) you might not use 5th gear if you not going over 50 mph. Also, if you use the A/C you will get probably 2 MPG less then without.

[MangoGT]

Subaru of America and my local dealership have maintained that my car doesn't have a problem.

 

After switching to Mobile 1 my fuel efficiency has definitely improved, and I even pulled 23-24mpg on a couple of tanks with highway only driving, keeping the car around 70-75mph.

 

It is still lower than I would like it to be, and lower than I think it should be. The only recommendation I received was from the manager at my local dealership--he said I should only use Shell V-Power (the only top tier gas in town). I've done that and I've kept nearly every single receipt since I started this thread and kept track of the mileage for each fill-up. I'm going to compile a spreadsheet and take it over to talk to the manager.