Increasing Gas Mileage

[cmiovino]

It's an EJ22E, 4EAT... grounding kit, prodrive oval tip... no other engine mods. Air filter is a little dirty, not bad. I've researched some stuff and decided I might try a new fuel filter since I have no idea when it was changed last. Just changed the oil with Valvoline Durablend full synthetic. Plugs were also changed a few months ago in summer.

And yea yea, everyone's going to say just lay off the throttle. Well, I do! A lot. Nearly never over 3K RPMs... usually around 2. No real quick acceleration or anything... under the speed limit.

I think it should be closer to about 25 or so if I baby it, which is why I think it may be something clogged or that just needs replaced. I don't like it dropping down to 18 and below. Think the fuel filter is a good start? (after what was replaced so far)

I know it's not the most fuel efficient car, but heck, if a $25 replacement part is going save me 3MPG or more... I'm interested

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[piker28]

so many factors lay into mileage its almost impossible to find out what it could be without a bunch of testing

[EvoSpeed]

pikers right we could all speculate it to death and get nowhere....

[cmiovino]

Originally Posted by piker28

so many factors lay into mileage its almost impossible to find out what it could be without a bunch of testing

Correct, but assuming it hasn't been changed in over 30K miles or something, would you guess it may need replaced and could be the cause?

[piker28]

well not sure what the specs were for your year, but for the more newer vehicles the fuel filter is replaced every 30k

tires inflated right? is the car dirty? you eat a extra burger at lunch? are you no longer following a car to work but instead in the lead, have you hit more traffic? do you plug your phone in to charge in the car? do you drive people around more?

well i think you get the point ha

[cmiovino]

Originally Posted by piker28

well not sure what the specs were for your year, but for the more newer vehicles the fuel filter is replaced every 30k

tires inflated right? is the car dirty? you eat a extra burger at lunch? are you no longer following a car to work but instead in the lead, have you hit more traffic? do you plug your phone in to charge in the car? do you drive people around more?

well i think you get the point ha

Right... but I've done nothing different since then. No more pasengers except my 135lb butt, just cleaned, tires inflated and checked regularly, no more traffic, no phones/adapters crap like that.

Just doing the same usual commutes to class and back. But, eh, I'll see if I can find out when the fuel filter was last changed. I have Subie bucks that will cover it.

[tagrp]

Winter Gas Maybe??? Colder Temps, longer warm-ups? First the Air filter is dirty this means it takes the engine more energy to draw the air in through the filter, on carburated engines it also cause more fuel to be drawn through the venturi causing a rich mixture(not a problem here). Try a different gas station maybe see if you get different results.

[cmiovino]

Originally Posted by tagrp

Winter Gas Maybe??? Colder Temps, longer warm-ups? First the Air filter is dirty this means it takes the engine more energy to draw the air in through the filter, on carburated engines it also cause more fuel to be drawn through the venturi causing a rich mixture(not a problem here). Try a different gas station maybe see if you get different results.

I'll try that... in fact, I've been using the same station AND same pump. And I'll ditch the spare wheel and jack... I have AAA anyways and never go that from home.

[Seraphinwolf]

Buy a trust worthy gas. (I fill at Shell's and Mobil's unless I'm about to be stranded cause I'm out of gas.)Turn off the defroster. Let the car warm up. Yes change the filter. Don't be so conservative on the throtle. It's the accelorating that kills you. Find a stable speed and stick to it. I actually get better milage at 5 over posted speed just cause I live in a hilly back roads area and it keeps me from having to accelorate as much. Highway vs. back roads will make a difference too. Yes the other stupid little factors matter too but just keep an eye on these too. Out side of actual modifications nothing can "help" milage. Milage is the reason I'm hoping to get my Impreza back this Saturday(basicly the same 2.2 you have just phase II) My SVX gets 21MPG but that's at 93 octane and I don't want to keep putting miles on my other wise low mile car.
-Gaddis

[Subyroo2.5]

Originally Posted by cmiovino

It's an EJ22E, 4EAT... grounding kit, prodrive oval tip... no other engine mods. Air filter is a little dirty, not bad. I've researched some stuff and decided I might try a new fuel filter since I have no idea when it was changed last. Just changed the oil with Valvoline Durablend full synthetic. Plugs were also changed a few months ago in summer.

And yea yea, everyone's going to say just lay off the throttle. Well, I do! A lot. Nearly never over 3K RPMs... usually around 2. No real quick acceleration or anything... under the speed limit.

I think it should be closer to about 25 or so if I baby it, which is why I think it may be something clogged or that just needs replaced. I don't like it dropping down to 18 and below. Think the fuel filter is a good start? (after what was replaced so far)

I know it's not the most fuel efficient car, but heck, if a $25 replacement part is going save me 3MPG or more... I'm interested

damn dude I get that kinda mileage railing around town...with 80+ on the highway and 3 or 4 110-115mph pulls.

btw gas is $3.49 for regular where I live!

[silver2004impreza]

Something you could try is running your tires over-inflated. I've read elsewhere that running too much pressure in your tires will make the center of the tread wear out prematurely/your ride quality will go to crap/you will spin off the road and wreck your car, and other than the very slight loss in ride quality, I think it's all rubbish.

I've got roughly 60 psi in my tires and I get low 20s per gallon out of my 2.5 sohc. I very rarely drive on highways, and the majority of the time, my engine is still cold by the time I get to work, so it never actually gets a chance to warm up. I know that it's causing all sorts of sludge to build up inside, but I try and take long drives twice a week to try and boil out any moisture that's accumulated inside my engine. I think that the highest fuel economy I've ever gotten was 28 mpg, when my wife and I were going on our honeymoon.

I've been running 60 psi in my tires since the car was new, and I haven't noticed any accelerated tread wear on either set of tires. My summer set (215/45R17 BFGoodrich G-Force Sport) is going on 50k miles, and they've still got a little less than half their usable tread life left. My winter set (205/60R15 Akuret Grip) has roughly 30k on them, and they're holding up just fine too. I've had them since the winter of 2004, and there's plenty of tread left on them. I'll probably run them next winter too, before I replace them. I haven't noticed any decrease in grip either, but I'm not driving on a race track either, nor do I drive on the street as if it's a race track.

I'm not worried about them blowing out either. I've seen a 155/80R13 tire with 100+ psi in it before. I don't know exactly how much air was in it, since the tire gauge only went to 100 psi (it's designed for heavy duty trucks), but it pegged the gauge.

YMMV

[sleepyfu]

sparkplug wires?
When I owned a 96 Legacy outback (5MT), I was getting at least 25mpg with pretty heavy right foot.

[DiuSee]

I'm surprised that no one has mentioned changing the automatic transmission fluid. that will make probably a greater effect, if it's a 13 year old car, and still hasnt done it.

[p8baller07]

lol @ 18mpg 2.5rs.

I'd sell your car - im getting 17-19 MPG average per tank on my Stage 2 WRX - and i have fun, trust me :P

[ballitch]

I would start with the usuall tune up, spark plugs, plug wires, new fuel filter. If you are buying that arco crap I would stop. I did a test of mileage on my car when it was bone stock, I got 2-3 mpg better with chevron, texaco, or shell. The winter 10% ethanol blend usually hits mpg's a little bit.

Mileage is affected by so many factors that you really cant point a finger at one particular thing, usually its the right foot. Have the o2 sensors ever been changed. When my front o2 sensor went bad I got 18 mpg city, if I babied it.

If I do alot of highway I can get about 27-28 mpg @ 75-80 mph.


Is your car throwing any CEL's (check engine lights)?



~Josh~

[Subyroo2.5]

Originally Posted by silver2004impreza

Something you could try is running your tires over-inflated. I've read elsewhere that running too much pressure in your tires will make the center of the tread wear out prematurely/your ride quality will go to crap/you will spin off the road and wreck your car, and other than the very slight loss in ride quality, I think it's all rubbish.

I've got roughly 60 psi in my tires and I get low 20s per gallon out of my 2.5 sohc. I very rarely drive on highways, and the majority of the time, my engine is still cold by the time I get to work, so it never actually gets a chance to warm up. I know that it's causing all sorts of sludge to build up inside, but I try and take long drives twice a week to try and boil out any moisture that's accumulated inside my engine. I think that the highest fuel economy I've ever gotten was 28 mpg, when my wife and I were going on our honeymoon.

I've been running 60 psi in my tires since the car was new, and I haven't noticed any accelerated tread wear on either set of tires. My summer set (215/45R17 BFGoodrich G-Force Sport) is going on 50k miles, and they've still got a little less than half their usable tread life left. My winter set (205/60R15 Akuret Grip) has roughly 30k on them, and they're holding up just fine too. I've had them since the winter of 2004, and there's plenty of tread left on them. I'll probably run them next winter too, before I replace them. I haven't noticed any decrease in grip either, but I'm not driving on a race track either, nor do I drive on the street as if it's a race track.

I'm not worried about them blowing out either. I've seen a 155/80R13 tire with 100+ psi in it before. I don't know exactly how much air was in it, since the tire gauge only went to 100 psi (it's designed for heavy duty trucks), but it pegged the gauge.

YMMV

You are insane if you are running more than the max PSI on the tire. When you over inflate tires that much the center will bulge out reducing the tires footprint on the road. This reduces traction in important situations such as sudden or emergency braking.

I can see going maybe 5-10psi over oem recommendations for fuel economy, but 60 PSI? I can just about guarantee that is about 8 psi over the maximum tire pressure rating for that tire! cmon man thats just dangerous!!

[cowboysuby]

93 octane never hurts...
more expensive, but better mileage- at least on my car.

[piker28]

^very untrue

[cowboysuby]

Originally Posted by cowboysuby

93 octane never hurts...
more expensive, but better mileage- at least on my car.

what part of this is wrong? i see a better throttle response and about 3-4 mpg better from mid-grade.

[SiFuSpEc]

hmm not too sure about the over-inflating tires bit...

thought i'd chip in,

i do pretty consistent 20 dollar fillups 87oct and 28-29mpg, on this winter gas,
this is a 05 RS with 90,500 miles on it, this is daily commuter mode..
in auto-x season that number varies

i do spark plug replacement every 14k (running copper, cheaper, don't mind replacing for piece of mind), castrol synthetic oil change every 5-6k w/purolator filter, SRI, borla header, 2.5" catback, underdrive crank pulley, blah blah blah, yes all my mods probably deteriorate MPG, so i'm pretty sure someone has to be getting better gas mileage..

then again, what plays quite a big factor is the right foot. driving across country with my buddy in his wrx, i was able to average 1-2 more mpg than he would just by how i used the throttle in accelerating and at highway speeds..

[giantturtle]

In addition to the suggestions above you might want to think about your charcoal canister, especially if it has never been replaced. It is responsible for drawing fuel vapor into the engine where it can be used to assist combustion. If the canister is defunct it can't pull that vapor in the engine and it just... well, vaporizes. Now, I don't know how much that would effect your mileage issue, but it stands to reason that it would contribute.

[cmiovino]

As far as tires go... they were down to about 30-32 ish... so I bumped it up to around 38 front, 36 rear. Max pressure is 44 for mine. The car feels sightly better though... no real increase in mileage.

I also though it could be how I'm driving, almost too conservative. I'd keep the engine working hard around 2K RPMs, let's say for a hill... when I could bump up to 3K a little before and have that momentum going up, thus the engine is working easier.

I'll combine that with taking out the spare wheel and jack stand for now. And next fill up, I'll try another gas station.

Btw, the tranny fluids were flushed before... around 60K I think.

Thanks for the responses.

[LTracer]

Originally Posted by SiFuSpEc

hmm not too sure about the over-inflating tires bit...

i do spark plug replacement every 14k (running copper, cheaper, don't mind replacing for piece of mind), castrol synthetic oil change every 5-6k w/purolator filter, SRI, borla header, 2.5" catback, underdrive crank pulley, blah blah blah, yes all my mods probably deteriorate MPG, so i'm pretty sure someone has to be getting better gas mileage..

then again, what plays quite a big factor is the right foot. driving across country with my buddy in his wrx, i was able to average 1-2 more mpg than he would just by how i used the throttle in accelerating and at highway speeds..

I've found the truth to be quite opposite from your statement above regarding mods and MPG deterioration. Intake and exhaust should allow the engine to breath better allowing greater efficiency (less energy spent drawing air in and pushing exhaust out). Underdriven pulleys, cams, heads etc are an entirely different matter. However with my bolt on mods I've personally noticed a 5-8% gain in highway fuel economy from stock.

Additionally, a WRX in it's stock configuration will get worse MPG on the highway than a RS (thinking 2-4MPG on the highway but feel free to correct me if I'm wrong). Holding everything else constant a N/A car will be more efficient on the highway than a turbo car. Not discounting your statement on driving habits and fuel efficient, there's just a lot more to the puzzle.

Apologize for the hijacking, just trying to keep it honest...

[formula91]

The 05 RS is rated at 22 City, 28 Highway. As inaccurate as these numbers are, I get about that much. I usually get 23 MPG, and I would say I'm half city and highway. I did baby it when it was new, but I think i went over 4000 RPM a couple times before 1000 miles.

it's about 23k now, and I started to see mileage slowly go up. It's more or less because I eased on the throttle I think. What can I say, I liked the car.

^That was just for a reference point^
I dunno how all of you are getting 28 and 29. Are you doing mostly highway driving?

As for the topic, because the car is older, I would say getting a full check-up/replacement/tune, either by yourself or with a trustworthy mechanic will help a lot. Because everything affects gas mileage, it would be worth your time to get everything checked on anyway, for more reasons than just gas mileage.

Also, it may be just a result of the engine aging. The volumetric efficiency of the car does go down as it ages afterall.
Your A/C is probably off right? Below 50MPH it's better to have A/C off. Above 50MPH it's better MPG to have it on, or at the least, just the vents.

--to the octane thing--

This is untrue to 99%.
Octane rating determines how much gasoline vapor can be compressed without spontaneously combusting. It has nothing to do with how much power it has within a volume. This was the assumption that leads people to believe that it will give better mileage. "Premium gas must have more power, therefore, I'll get better gas mileage because I'll be getting more power from the same volume."

This is not really true, because although octane has more carbon than heptane (carbon burnt = energy) (which where the meaning came from. IE 87 octane = 87% octane, 13% heptane) gasoline contains more than just those two now. Acetone has a high (over 100) octane rating, but we can say that acetone doesn't have octane! How can one have over 100% octane in a given volume right? The other hydrocarbons and additives in gasoline (quality gasoline...) help the fuel vaporize, and therefore burn efficiently and cleanly. Octane rating has become to mean how much it can be compressed before producing engine knock. (spontaneous combustion in the chamber.)

It should also be noted that octane doesn't burn as fast as heptane. Even though there's more carbon, there are more covalent bonds and the molecule is overall heavier. Heavier molecules tend to have a harder time vaporizing, as well as reacting. Therefore, because it doesn't burn as well, one can say that it's actually creating LESS power for an engine that doesn't need it. IE a compression ratio that's not high enough to get a knock. The more compression the faster things burn as vapor, therefore, the slower burn rate won't be found on high compression/turbocharged engines. (I think I'm right about this one)

It's all in your head, or changes in driving style, or something else. My personal belief is that if you find something in MPG, it's not just one thing you can attribute to. The person's mind really does create physiological changes....

http://auto.howstuffworks.com/question90.htm

--To the winter gas thing--
There really isn't "bad stuff" that they put into winter gas that makes your car run all weirdy, sort of.
They put more additives in the gas, this is true, but really, summer gas is made up the same stuff. It's just that, they don't take out a few things, and they add a few things, which makes the winter gas prices more expensive. More importantly, they put in lighter hydrocarbons and oxygen bound fuels, all with rather high octane ratings. This helps the fuel vaporize in otherwise, crappy crappy conditions for vaporization. It's so cold in a lot of places during the winter that fuel has a bad time vaporizing, so it can't burn. With oxygen bearing compounds and lighter fuel, I don't see this as the reason for lower gas mileage.

Simply put, the lower gas mileage comes from the crappy winter conditions itself. It's colder. Cold engines has AFRs as rich as 4:1. Cranking it's 1.5:1. Winter time, warmed up engines may see AFRs closer to 12 and 13. Richness all equates to lower gas mileage. The oxygen bearing compounds found in gasoline make the ideal stoich ratio around 14.3 instead of 14.7. But the ambient temp of the engine really makes that point moot. Really, it's just making the ECU frustrated, that's why MPG goes down in the winter.

http://www.zhome.com/ZCMnL/PICS/wint...winterGas.html

[ZRS]

GC FTW! Im getting a total average mpg of around 30.

2000 RS. Stock but for a snorkel removal.