lousy gas mileage

[lytnin88]

I have an '03 Forester, auto trans, with 67K miles on it. About the best mileage I can get is 22 mpg, and this is mostly highway driving. Recently changed air filter, fuel filter, spark plugs (Denso), keep tires inflated at 29 psi front, 36 rear. Still using dino oil. Am I missing anything?

[Subaru Jim Maple Ridge]

I have an '03 Forester, auto trans, with 67K miles on it. About the best mileage I can get is 22 mpg, and this is mostly highway driving. Recently changed air filter, fuel filter, spark plugs (Denso), keep tires inflated at 29 psi front, 36 rear. Still using dino oil. Am I missing anything?

 

Try putting the same pressure in all the tires. That way, all of your tires will have the same circumference and the rears won't be pushing the fronts down the road. Recheck your mileage and get back to us.

[Tiny Clark]

I always thought a little more in the fronts (2lbs), due to added weight of the engine and tranny.

[OB99W]

I have an '03 Forester, auto trans, with 67K miles on it. About the best mileage I can get is 22 mpg, and this is mostly highway driving. Recently changed air filter, fuel filter, spark plugs (Denso), keep tires inflated at 29 psi front, 36 rear. Still using dino oil. Am I missing anything?

Some people might call 22 mpg "somewhat below average" or even "average", not "lousy", and as you probably know, there are lots of things that can cause fuel mileage to suffer. But first...

 

Those are interesting inflation pressures; I believe spec is 29f/28r. While the fronts are at spec, you might try another couple of pounds there, which shouldn't stiffen the ride too much or cause wear problems. Unless you're hauling very heavy loads (in which case, that might explain where the fuel is going), 36 psi at the rears is high. Lightly loaded, they should be a pound or so lower than the fronts; carrying more weight, equal to the fronts or very slightly higher than them. Pressure is, of course, measured with tires cold. Uneven tire wear or inflation pressures can cause drivetrain problems.

 

With a bit more info, maybe we can offer other suggestions. Some questions:

1) Are you sure your tire gauge is accurate?

2) Did you buy the Forester new?

3) Did it ever get better mileage?

4) Is the terrain flat or hilly where you mostly drive?

5) What viscosity oil are you using?

6) Can we assume there are no driveability problems, unusual sounds, or other possible clues?

 

--OB99W

[nipper]

Also a forester does fall in the "rolling brick" catagory.

 

Another factor to look at is your tires. They can have a lot of effect on milage. The more sticky the tires are (handling) the more rolling resistance, the lower the gas mileage. High mileage tires tend ot give better gas milage. Also wht kind of terrane do you drive on on the highway. If its alot of hills, and you find the car hunting alot for the right gear in Drive, go to d3 as that may help. ALso you can get a vaccum gauge. The higher the needle the better the gas mileage. That would give you some feedback for your left foot.

One last thing, what condition are your O2 sensors in?

 

 

nipper

[cookie]

My Forester turns in a regular 25 in mixed city and highway. I go down a bit when they give us the smog fuel or if traffic is very bad.

[friendly_jacek]

You pressures are indeed out of whack but doubt if it has any bearing on the MPG issue. Currently I keep pressure in my legacy at 40/40 and have about the same MPG more or less. Interestings, tire pressure is by far most common advice given for MPG problem but is least likely to affect the MPG, at least in my experience.

Is someone doubled MPG by doubling PSI, please let me know!

 

 

BTW, i invested a lot of time and money in troubleshooting my poor MPG (18/24 city/hwy) to conclude that some cars are good and some are bad concerning MPG. Also, some people have lead food, but that is a secondary issue.

 

The highly touted saving by increasing PSI or going to synth (aka low viscosity) oils give marginal results only, as I tried both with no results.

 

One more thing: some people swear by the FWD fuse, but it is bogus, too. Also, forget ECU resets, grounding mods and similar nonsense. Been there.

[Stinky fingerz]

You pressures are indeed out of whack but doubt if it has any bearing on the MPG issue. Currently I keep pressure in my legacy at 40/40 and have about the same MPG more or less. Interestings, tire pressure is by far most common advice given for MPG problem but is least likely to affect the MPG, at least in my experience.

Is someone doubled MPG by doubling PSI, please let me know!

 

 

BTW, i invested a lot of time and money in troubleshooting my poor MPG (18/24 city/hwy) to conclude that some cars are good and some are bad concerning MPG. Also, some people have lead food, but that is a secondary issue.

 

The highly touted saving by increasing PSI or going to synth (aka low viscosity) oils give marginal results only, as I tried both with no results.

 

So did you do any mods/improvements that actually gave you an improvement in gas mileage. I am looking for a way to get better MPG and am looking for advice.

 

One more thing: some people swear by the FWD fuse, but it is bogus, too. Also, forget ECU resets, grounding mods and similar nonsense. Been there.

 

So did you do any mods/improvements that actually gave you an improvement in gas mileage. I am looking for a way to get better MPG and am looking for advice.

[LosDiosDeVerde86]

I have an '03 Forester, auto trans, with 67K miles on it. About the best mileage I can get is 22 mpg, and this is mostly highway driving. Recently changed air filter, fuel filter, spark plugs (Denso), keep tires inflated at 29 psi front, 36 rear. Still using dino oil. Am I missing anything?

 

join the club.

[97OBW]

i got an avg. of 26 of mixed, but mostly highway driving. my tire pressure was 6lbs low at this time...does 32/30 front rear sound good for a 97obw that wants max. economy?

[tunered]

talked to 3 route drivers[mail men] here in my area last year,they said they got 3-5 more mpg with fuse in,in the summertime.i tryed mine in all summer this year and averaged 3 more mpg.yours may very but it is one thing that WILL help,not much but some. ps what i did to mine was i put a switch under the dash,ran two wires from the fuse holder,put inline fuse on one wire[dont matter which] so i didnt have to crawl under hood all the time,the switch will not change after the car is started,you will have to shut off ignition and change switch position and then restart.

[lytnin88]

Try putting the same pressure in all the tires. That way, all of your tires will have the same circumference and the rears won't be pushing the fronts down the road. Recheck your mileage and get back to us.

 

 

I'll try that. THanks for the advise.

[lytnin88]

Some people might call 22 mpg "somewhat below average" or even "average", not "lousy", and as you probably know, there are lots of things that can cause fuel mileage to suffer. But first...

 

Those are interesting inflation pressures; I believe spec is 29f/28r. While the fronts are at spec, you might try another couple of pounds there, which shouldn't stiffen the ride too much or cause wear problems. Unless you're hauling very heavy loads (in which case, that might explain where the fuel is going), 36 psi at the rears is high. Lightly loaded, they should be a pound or so lower than the fronts; carrying more weight, equal to the fronts or very slightly higher than them. Pressure is, of course, measured with tires cold. Uneven tire wear or inflation pressures can cause drivetrain problems.

 

With a bit more info, maybe we can offer other suggestions. Some questions:

1) Are you sure your tire gauge is accurate?

2) Did you buy the Forester new?

3) Did it ever get better mileage?

4) Is the terrain flat or hilly where you mostly drive?

5) What viscosity oil are you using?

6) Can we assume there are no driveability problems, unusual sounds, or other possible clues?

 

--OB99W

 

1)yes

2)yes, I bought it new

3)not that I measured

4)pretty flat

5)5W-30

6) I think that's a reasonable assumption.

[nipper]

I'll try that. THanks for the advise.

 

Just remeber how mailmen have to drive, repeatedly stop and go, so i dont think that will work for you. They may save gas from the initial iniertia of getting parts moving, but i seriously doubt that gain is true. You still have to move all the same parts. Only time you gain MPG in a 4wd vehical like that is if you can unlock the hubs and not srive the differnential and driveshaft.

Alos compare your forester with real world gas milage on other SUVs. i rented a ford escape for 3 weeks, the best the thing did was 18mpg, the worst it did was 12. It was rated alot higher the that. If your going to drive around in 2wd, might as well sell it and get a 2wd car.

 

 

nipper

[lytnin88]

Also a forester does fall in the "rolling brick" catagory.

 

Another factor to look at is your tires. They can have a lot of effect on milage. The more sticky the tires are (handling) the more rolling resistance, the lower the gas mileage. High mileage tires tend ot give better gas milage. Also wht kind of terrane do you drive on on the highway. If its alot of hills, and you find the car hunting alot for the right gear in Drive, go to d3 as that may help. ALso you can get a vaccum gauge. The higher the needle the better the gas mileage. That would give you some feedback for your left foot.

One last thing, what condition are your O2 sensors in?

 

 

nipper

 

Thanks for the suggestions, nipper. It's pretty flat where I live, so terrain wouldn't be a factor. How do you go about testing O2 sensors? Will OBDIII scanner tell you if they need replacement? The front one looks OK: haven't seen the rear one.

[1 Lucky Texan]

-----snip------the switch will not change after the car is started,you will have to shut off ignition and change switch position and then restart.

 

I didn't realize that. I guess, instead of a constant 12v or ground applied to the duty solenoid C, the fuse position is perhaps just a signal to the ECU.

 

hmmmm....

[nipper]

The fuse for AWD bypasses everything and energizes the solenoid directly. This deactivates the RWD.

 

nipper

[nipper]

Thanks for the suggestions, nipper. It's pretty flat where I live, so terrain wouldn't be a factor. How do you go about testing O2 sensors? Will OBDIII scanner tell you if they need replacement? The front one looks OK: haven't seen the rear one.

 

a scanner should tell you the outputs of the o2 sensors, but im not sure. You can also throw a multimeter on them and see what the reistance is. 02 sensors have a big part on MPG, especially once the car gets over 80K, they can start showing thier age. They can and usually do last longer, but its a good place to start.

 

nipper

[1 Lucky Texan]

The fuse for AWD bypasses everything and energizes the solenoid directly. This deactivates the RWD.

 

nipper

 

That's what I thought til I saw his post. I think grosgary also said the ECU will detect the fuse position on startup - so some type of feedback is involved.

 

If someone has a switch in the FWD circuit - will the FWD light be lit if the switch is flipped while running? Or only after startup? It DOES seem folks have confirmed the solenoid FUNCTION is controlled while running. Just seems weird how the ECU would detect this stuff differently.

 

I doubt I'd need to ever do this mod. I just find it interesting.

[OB99W]

1) Are you sure your tire gauge is accurate?

2) Did you buy the Forester new?

3) Did it ever get better mileage?

4) Is the terrain flat or hilly where you mostly drive?

5) What viscosity oil are you using?

6) Can we assume there are no driveability problems, unusual sounds, or other possible clues?

1)yes

2)yes, I bought it new

3)not that I measured

4)pretty flat

5)5W-30

6) I think that's a reasonable assumption.

Well, your answer to my 3rd Q is a bit ambiguous, but I'll make some assumptions. Since you've had the Forester from new, if it never got better gas mileage, then recently-defective parts isn't too likely. Because you haven't mentioned any drivability issues, I'm assuming that the car wasn't ever in an accident that could have caused some suspension misalignment, and that it isn't dragging tires somewhat sideways. Even if you've just hit some curbs hard, it might be worth having the alignment checked if it hasn't been done recently.

 

On the other hand, perhaps you only began checking mileage when gas prices went up. A car running California gas (usually oxygenated more than most) tends to get poorer mileage than average, so 22 mpg may be normal for your driving style.

 

California brings up another question - was the Forester bought there?

 

O2 sensors, as you might expect , sense O2; if the gas is heavily oxygenated, they could see a lean enough exhaust to tell the computer to enrich the mixture (send more gas). Even if the O2 sensors are fine, under these circumstances (and especially if the computer is calibrated for a less-oxygenated fuel), mileage goes down somewhat.

 

--OB99W

[nipper]

That's what I thought til I saw his post. I think grosgary also said the ECU will detect the fuse position on startup - so some type of feedback is involved.

 

If someone has a switch in the FWD circuit - will the FWD light be lit if the switch is flipped while running? Or only after startup? It DOES seem folks have confirmed the solenoid FUNCTION is controlled while running. Just seems weird how the ECU would detect this stuff differently.

 

I doubt I'd need to ever do this mod. I just find it interesting.

 

Fuse has no feedback to the ecu, nor to the transmission computer. The fwd light will be on anytime that circuit is energized.

 

nipper

[Subaru Jim Maple Ridge]

My tire supplier, a wholesaler only, advises that all tires should be run at their maximum rated pressure for best economy and to reduce tire wear. Underpressure results in weaker sidewalls and shoulder wear. Also, he advises that there should be no differential in front and rear pressures as the actual circumference of the tire depends upon the tire pressure, not the load upon the tire. This is a very important aspect for all owners of 4WD and AWD to consider.

 

I have requested an opinion directly from the manufacturer to confirm or dispute this position. In the interim, is anyone aquainted with a person 'in the know' from whom we could get an educated opinion?

 

I always went by the pressures listed on the door post, except for big mags which required full pressure to keep the center of the tread on the road. My tire buddy straightened me out a few years ago.

 

I am now driving an '87 DR sw. I can change in and out of 4Hi just by dropping my foot off the gas and pushing gently on the transfer lever.

It would follow that if your gears are binding, so are your tires.

[cookie]

I checked my current mileage on my Forester yesterday. Right now I am on winter fuel here in the Bay Area and I have a five speed which should do a tiny bit better than his car if he has an automatic.

It has been raining lately which does not help my mileage as it affects traffic and I run with more electrical load. I got 23.9 on my last tank. This is actually fairly good for winter for me in this area.

I have been running this car for 40,000 miles now with no change in the mileage except seasonally and traffic.

My car gets checked regularly by me, smogged, and yesterday it went to a friend's shop where they insisted on checking everything becuse I am going on an Xmas trip. Two mechanics ran the checklist on the car and they stuck it on the smog machine to see if the mixture was good. They think this is the best running old Subaru that they see and they do the overflow and smog work for our local dealer. All they charged me was an oil change by the way...

This makes me think that my Forester is probably in the ballpark for being an average one for fuel mileage. I think if I was running rich the smog machine would pick it up.

[bfg9k]

BTW, i invested a lot of time and money in troubleshooting my poor MPG (18/24 city/hwy) to conclude that some cars are good and some are bad concerning MPG. Also, some people have lead food, but that is a secondary issue.

 

Same here, but I refuse to believe that some cars are 'just bad' - they're mechanical devices, SOMETHING must be different between the good and bad mileage ones.

 

My next step is to do the rear O2 sensor in my '98 Legacy (19 city/22 highway). By way of comparison, on the identical commute where the Subaru does 22 mpg my Saab 9-5 wagon gets 31 mpg, so I'm sure it's not my driving. After that I start looking at the emissions system.

[nipper]

My tire supplier, a wholesaler only, advises that all tires should be run at their maximum rated pressure for best economy and to reduce tire wear. Underpressure results in weaker sidewalls and shoulder wear. Also, he advises that there should be no differential in front and rear pressures as the actual circumference of the tire depends upon the tire pressure, not the load upon the tire. This is a very important aspect for all owners of 4WD and AWD to consider.

 

I have requested an opinion directly from the manufacturer to confirm or dispute this position. In the interim, is anyone aquainted with a person 'in the know' from whom we could get an educated opinion?

 

I always went by the pressures listed on the door post, except for big mags which required full pressure to keep the center of the tread on the road. My tire buddy straightened me out a few years ago.

 

I am now driving an '87 DR sw. I can change in and out of 4Hi just by dropping my foot off the gas and pushing gently on the transfer lever.

It would follow that if your gears are binding, so are your tires.

 

 

i go buy the tire pressure marked on the tire if the tires have been replaced with differnt tires then stock. Tires should run at their max pressure when hot (basically if you drive to an airpump they are hot) and checked with major temperature changes.

All tires need to be the same circumfrence within 1/4 inch (per subaru).

You are correct though. i had an 87 GL that i could shift in and out of 4wd as smooth as silk, unless one tire was a little low on air.

 

nipper