Draco Posted June 23, 2004 Share Posted June 23, 2004 Ok now this is pathetic I should be getting up to 30mpg right? My last fill up was just under 20mpg, now this was all city driving but still seems quite low. The troubleing thing is when I do highway driving I never really get above 25mpg and usually am at 23mpg or so. This car has a little 4 cylinder, come on! Gramps V-8 mercury boat will get 25 at times! I have a '97 Legacy GT Sedan, 2.5 DOHC AWD Manual. It only has 46k miles. Car would be perfect if I could get up these mpg, my old '91 accord had a 2.2 and got 34mpg. I put Mobil 1 5w30 synthetic with a purolator filter in 2k ago, along with a new air and fuel filter, pcv valve and spark plugs. One thing I did notice is 2 of the spark plugs did seem to have more what I believe is carbon deposit on them then the others. It didn't seem like an extremely high amount, but it was noticeably more then the other two. Not sure if this could mean anything. I have heard you can replace O2 sensors and that can help, but I'd be very surprised if it goes out at 46k even though it is an 8 year old car. I'd rather not just replace something blindly, and I believe there are two sensors which would probably cost over $200. Is there a way to test these? I was thinking of buying one of those OBDII readers, would those help at all? I think you can get readings for a variety of sensors so maybe I could tell if something is out of spec, but how would I know what the readings should be? This does sound like a neat tool so I'd much rather spend ~$100 on something I know would be useful then replacing 02 sensors which may not help at all. Any other suggestions of what I should do? Quote Link to comment Share on other sites More sharing options...
Guest jclay Posted June 23, 2004 Share Posted June 23, 2004 Have you tried a fuel system cleaning? if the intake valves and conbustion chambers are clogged with carbon, that could cause the engine to run ineffiecently. If you've never had it done, take it to a shop, then regular doses of fue system cleaners from your local auto parts store should due the trick. Quote Link to comment Share on other sites More sharing options...
Commuter Posted June 23, 2004 Share Posted June 23, 2004 I have a 97 OB, 2.5L, Phase I engine, auto, AWD. I routinely get about 25mpg with virtually all highway driving at 70mph. I've seen some claim up to 30, but I have never come close to that. I now have almost 250k miles on my car. These engines are known for carbon problems. I've been thru it, which really surprised me with all the highway miles I travel. However, I didn't suffer much, if any loss in gas milage. My issue was a low rpm hesitation. It will take something like a MotorVac treatment to properly get rid of the carbon. After that, routine use of some sort of treatment should keep the carbon at bay. The second time I ran into the carbon issue, it was a result of a weak O2 sensor. I did not have any codes. The mechanic said it was 'cycling' fine, just a bit slow in its response. I finally changed the O2 sensor anyway. My 'hesitation' drastically lessened, then gradually went away after several weeks. But again, I was not suffering much in the MPG. 1, maybe 2 at the most. It did return to the 'usual' after changing the sensor. You don't have many miles, but you have 8 years of 'run time'. The senor is probably nearing the end of its life. As an aside, my E-test didn't look very good to me 2 years ago (old sensor), but it did pass. This year, the E-test was quite a bit better (new sensor). (Even at that, the E-test results for this engine look pathetic next to my wife's 99 Honda Odyssey.) I'm not sure what else to suggest. I'm not saying that carbon is the only issue. I just wanted you to be aware of what I have learned and experienced. Commuter Quote Link to comment Share on other sites More sharing options...
hklaine Posted June 23, 2004 Share Posted June 23, 2004 My '96 2.2 gets ~22 mpg on average, thats a mix of highway and backcountry. I haven't taken it on any trips where I would burn a full tank on the highway but even with conservative driving the gas mileage isn't great. I think you will find (or to some extent have found) that others will concur. -Heikki Quote Link to comment Share on other sites More sharing options...
mattocs Posted June 23, 2004 Share Posted June 23, 2004 My 2.2 Outback gets 24MPG average. Up to 30 on highway @ 55MPH. When my air flow sensor was going bad I get really bad mileage. Quote Link to comment Share on other sites More sharing options...
on3letsgo Posted June 23, 2004 Share Posted June 23, 2004 I'm getting 25mpg on average in my auto 97' 2.5L OB. And that is city driving. But it still isn't running right. Quote Link to comment Share on other sites More sharing options...
Draco Posted June 24, 2004 Author Share Posted June 24, 2004 Ok.... well thanks for the suggestions. The carbon cleaning is a good idea. I've heard of the MotorVac before so maybe I'll give it a try and see if the shop has any other ideas. I might replace an o2 sensor too as it looks like that has helped some people. I thought I read that there were two o2 sensors, now do you replace both of them or is one replaced more often? What is an E-test? Sounds like these subarus just don't get as good of mpg as you'd think they would for their size as well as their engines. Must just be the AWD and less effiecent engines as say hondas and toyotas. Quote Link to comment Share on other sites More sharing options...
Commuter Posted June 24, 2004 Share Posted June 24, 2004 Ok.... well thanks for the suggestions. The carbon cleaning is a good idea. I've heard of the MotorVac before so maybe I'll give it a try and see if the shop has any other ideas. I might replace an o2 sensor too as it looks like that has helped some people. I thought I read that there were two o2 sensors, now do you replace both of them or is one replaced more often? What is an E-test? Sounds like these subarus just don't get as good of mpg as you'd think they would for their size as well as their engines. Must just be the AWD and less effiecent engines as say hondas and toyotas. Front O2 is involved with the fuel maps. The back one just checks if the cat is doing it's job. E-test: Emissions test. Hydrocarbons, NOx, etc. The Phase II engine inproved the fuel milage some. The SOHC system has less frictional loss. But yeah... they are not exactly great engines in terms of efficiency. Subaru argues that the AWD is only a small penalty. And they are right... but small is still something. 5% I'm guessing, maybe more? It's there. You can do lots of little things to improve fuel milage. Try different brands of gas (that can be surprising sometimes). Synthetic fluids in the diffs and tranny. Free flowing air filter (maybe). Get rid of any excess weight in the car. Take off roof cross rails (if you have them). Proper tire pressure. Better tires. But these are are very marginal improvements in most cases. Commuter Quote Link to comment Share on other sites More sharing options...
legacy2.5 Posted July 6, 2004 Share Posted July 6, 2004 i get 22-25 mpg around towm with my 97 2.5 legacy gt, i used to get around 20 or so and my cars runs perfect. when i started installin aftermarket exh. components (borla header, magna flow muffler) my mpg's started going up. how clean is your upper intake area, i would recommend a de-carb, and maybe a fuel injection flush with that mileage. do you maintain your vehicle on a routine basis??? Quote Link to comment Share on other sites More sharing options...
jcniest5 Posted July 6, 2004 Share Posted July 6, 2004 It seems like you guys get so much of your gas! Mine only gets 17-20 MPG max in highway. Worse in the city (15-18 MPG). Not sure if mine were to be manual would make much difference at all. Would it? Quote Link to comment Share on other sites More sharing options...
legacy2.5 Posted July 6, 2004 Share Posted July 6, 2004 i have an auto tranny for now, im looking for a manual car for parts swap Quote Link to comment Share on other sites More sharing options...
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