Solving poor Subaru mileage

[bfg9k]

Hi all. I've asked this over at ultimatesubaru.net, but I'm going to try again here.

My '98 Subaru LEgacy L (2.2L engine, auto) gets poor mileage: 20 mpg highway, it's rated at 23 city/30 highway.

In the past year, I've had the tranny rebuilt (due to internal failure), switched to synthetic oil (RP 75w90 in diffs, currently Pennzoil Plat 5w30 in engine), replaced the O2 sensor, engine coolant temp sensor, PCV valve, spark plugs, and spark plug wires. Oh, and the thermostat, which was failing. Nothing has worked... I'm running out of things to try. Fortunately this hasn't cost me much due to DIYing most of it (except the tranny rebuild, yeouch that one hurt). I have not touched the ATF since it's still under warranty ;-) I did the temp sensor last week but judging from the fuel gauge & odometer that didn't work.

Can any BITOG're make any other suggestions? My commute is 95% highway, typically 70 mph in the mornings, 50-70 in the evenings, I use cruise control much of the time and I don't have a lead foot. I'm at a loss to understand what's going on here. I'm considering dropping in a bottle of AutoRX and seeing what happens with that process.

 

[bulwnkl]

If you can tell me how to stop my '91 XT6 from slightly surging during hard acceleration, I'll fix your Legacy's fuel economy. LOL!

Seriously, though, I don't have any good ideas. Maybe it's just one of those that doesn't get good mileage. Replacing everything should correct it, but sometimes it doesn't. Have you checked compression or done a leak-down, by chance? Not likely but...
What about wheel bearings, alignment, slightly dragging brakes (including e-brake)? Tire pressures? Okay, I'm sure all this occured to you already, but like I said, I don't have any good ideas.

Good luck.

 

[bobo]

When was the last time the fuel filter and air filter were replaced?

 

[Jim 5]

I just got a 5 mpg increase using AutoRX (see the sponsors section). I would give that a try.

If you want to do some research, check the additives section.

A good friend of mine has a 2002 impreza with the 2.5L engine and awd. He's not happy at all with the fuel economy. AWD sucks alot of gas, however, you should be reaching closer to the estimated fuel economy.

 

[bfg9k]

Hi, here's some more info. 111k miles, I've owned it for two years. The first year, my wife just drove it around town so I never really noticed an mpg issue. The past year it's been my commuter since she moved up to Saab 9-5 wagon. I noticed the poor highway mileage right away! The car is full-time AWD.

The fuel filter was done last fall, and I also put in a K&N air filter at the same time. Average yearly miles is 6500.

My mechanic says the brakes are in good shape and aren't dragging.

I've got 1 year old Nokian WR all-seasons (kick-butt, by the way) on, with the Subaru recommended air pressure. The engine doesn't consume or leak a drop of oil, and I have on occasion run a bottle of the Redline fuel injector cleaner through.

You see my frustration level here!

I'm utterly mystified. I occasionally have a gas smell on startup in the mornings, if that's a clue. Thanks everyone!

 

[bfg9k]

Oh, and I've always used 10w30 or 5w30 oil, as per the owner's manual.

 

[brianl703]

Has this vehicle ever had an emissions test and if so what were the results?

 

[mechtech]

How about a partially clogged cat. converter?
Is the torque converter locking up OK?

 

[bfg9k]

Hi Brian703 - the car passes its annual MA emissions test with no trouble.

mechtech - I've never considered a cat converter problem. If it passes emissions, could this still happen? I'm considering swinging by the transmission shop that did the rebuild since they'll do a free electronic diagnosis (they do 'em for the life of the car once they do a major service). I can feel the torque converter operating though, and the highway RPMs look right (~2700, 65 mph).

I swear I'm not making all this up!!

 

[ediamiam]

Pretty tough. In the time you've had the car, you can't even verify that its gotten anything better than 20. Must be time for that cure in the bottle, you've tried everything else. auto-rx it.

 

[bobo]

Not that it will help much but you might want to add a little more air to the tires.

Does this car have a knock sensor? Can the vehicle be checked for codes?

 

[bfg9k]

It just occurred to me that perhaps there's a fuel leak somewhere in the fuel line...that could account for the gas smell in the mornings.

I just ordered a bottle of Auto-RX.

 

[bulwnkl]

Ever pulled an oil sample? If there's an injector problem or something (gasoline smell you mentioned made me think of it), Dyson Analysis might be able to spot it for you. You can have injectors ultra-sonically cleaned very inexpensively if you can afford to be without the car for a week or so while you take them off, ship them, and wait to get them back.

 

[Ugly3]

Compression test is next in line.

 

[ediamiam]

aah, the smell of fuel in the morning. now we're getting somewhere, something concrete to work with. that's something you can take to your mechanic. whoops, wait, you are the mechanic. what's your plan of attack ? auto-rx won't fix yur fuel leak.

 

[michaelc80]

Don't know if this would work for you-my 05 Outback gets about 28 MPG at 70-75. If I'm on 2 lane roads doing a steady 58 I can get about 32 MPG. That 10-15 MPH makes a huge difference. My 05 is also rated at 23 city/30 highway.

I would also run AutoRX in it for a couple of cycles. Might help increase the mileage some.

 

[Eddie]

Is your AT shifting into 4th gear and the torque converter locking up at 35-40 mph??

 

[JHZR2]

The driveline losses from AWD can be significant... then again, EPA should have tested the AWD model, making this a non-issue. roofracks, certain tires, etc. can reduce this by a few MPG.

Id have to guess that there is something wrong with the transmission/rebuild... Was the MPG bad before it went south?

Maybe the O2 sensor is lazy but not bad enough to set a code... or some sort of problem like that, which is really hard to find, doesnt quite set a code, but still exists and causes trouble...

JMH

 

[oilyriser]

quote:

---

Originally posted by bfg9k:
It just occurred to me that perhaps there's a fuel leak somewhere in the fuel line...that could account for the gas smell in the mornings.

---

Bingo!


Check the areas near all the fuel lines, fuel rails and injectors for clean spots or other signs of leakage. Fortunately, it's a distributorless ignition system, with no sparks to cause a fire.

 

[deepsquat]

are these cars full time 4 wheel drive ? the reason i ask is , you may want to take it to a shop and have it dyno tested...perhaps something will show there...way under powered for instance??? hence to much gas needed to push the car ? call around for a dyno that can handle your car ..test shouldn't cost too much...compared to the gas you are going through !