Better gas mileage mods/suggestions?

[OutbackMat]

My wife's '97 4EAT-equipped BG is currently getting around 20-24mpg. That's with her revving to around 4K in 1st and 2nd. The tires and suspension are new, the plugs and wires, headgaskets, and timing belt have been taken care of...and the car never seems to do better than 25mpg, even when cruising...granted at 75, but hey.
Everything is stock, save for the warm-air-intake filter I stuck on the end of the MAF. I'm used to Neons where you can do some weight redux, add a better muffler, a CAI, and a little intake manifold massaging and you gain 5+mpg. What can we do for the BG?

[Huffer]

You can do all of that to the BG.

What you might want to try doing is cruising a little slower. I will yield 29mpg on freeway cruising, I very rarely go over 65mph.

The AWD is heavy, so that limits you.

You could also try new fluids in the transmission and rear diff. A lighter weight engine oil will also help reduce overall friction.

[DOOK]

my BH5 is only getting like 22 around town... freeway 26 tops... I hate it

[Mikey97D]

I don't think your going to see the huge gains in mpg like you've done with the Neon, but you should be able to get 30+ mpg on the highway stock by changing your driving habits. So, the first modification would be to driving habits. Shift at 2500 rpm and slow highway down to 70 mph should get you close to 30 mpg.

Other modification like cold air intake and exhaust would produce mpg, but not if you don't use modification #1. Tire pressure at 35 psig will also help. On your year Subaru, I think the Neon coil modification will give you a better spark which should give better mpg which is in the DIY (maybe you wrote that one?, I don't remember who wrote it,but I'm a noobie here). Also, you may see some gains if you do the additional ground wiring (also in the DIY). Lastly, you may want to try some of that Sea Foam to clean the gunk out of the car. I'll post something else up if anything comes to mind.

I've been keeping track of my mileage since I bought my car in May. I've gotten as low as 23.1 mpg to a high of 27.1 mpg with an overall average of 24.6 mpg. The variation is due to the idiot behind the wheel named Mike. The car needs plugs & wires still and the EGR cleaned. I just changed the air filter and added Sea Foam to the fuel last night. Hopefully I can measure some change from those two items.

One other item I've been contemplating is the ScanGauge which will give live updates of fuel consumption plus a multitude of readings. I'm not sure I could reason the costs vs gains to make it worthwhile for myself.
http://www.scangauge.com/

Good luck!
Mike

edited again because I'm an idiot who can't spell or use grammar correctly. Good thing I'm using Firefox. :lol:

[OutbackMat]

Funny you should mention fluids, Huffer. The car needed a new diff solenoid and in the process, we flushed the center (front?) diff with about 25 qts of fluid. I've been using 10W30 in the summertime and 5W30 in the winter....with 116K on the car, I'm definitely bypassing a 0W synthetic. I think the rear diff got new fluid a few years ago, so we might be due. Should we flush it with a ton of fluid the way we flushed the front diff?
Tires have always been run hard--meaning about 5psi below the max pressure so as to minimize the contact patch during normal driving. I think they're at 38 right now (max is 41?).
I don't know anything about a Neon coil pack upgrade, but they sure look similar. Have to check that out. Same with seafoam. I was planning on just running some combustion chamber cleaner (Ma Mopar makes great stuff) at the next oil change but I'll read up on Seafoam.

EDIT: Hey, I know the TB has a coolant line running through it. I imagine using a copper hosebarb to bypass it would help things...yes?

[Huffer]

Well you could run 5w30 year round... if there's no clanging or other noise, 5w30 is rated for year round use. I run Castrol Syntec 5w30 in my car all year.

The rear diff can just be drained and refilled... you could do a flush if you want but that's just expensive.

Tire selection can also make a big difference to MPG - stickier tires or tires inappropriate for the conditions will force the car to work harder to move the vehicle.

I have a ScanGaugeII and it paid for itself in less than a few months when I was able to consistently diagnose CELs and fix them without having to run to a parts store for diagnosis. The 4 gauge display (which includes MPG) is great too.

[deadlydave]

you could get a lighter crank pulley, take a bunch of stuff like spare tires out of your car, and get some lighter wheels. Taking the trailer hitch mount off the car when not in use also saves a little.

Also, tell her to shift at 2100rpm. Don't give me guff about the engine 'not having grunt that low'. Below 2300 RPM my baja turbo's engine is just a low-compression 2.5L engine with a big obstruction in the intake, and my car outweighs your outback by at least 400 pounds. Just drive 'er gently.

[Hocrest]

How old is the O2 Sensor?

[OutbackMat]

Huffer, in PA, we get some pretty hot days and the temp range for 5W30 is right on the edge, so just to be safe, I run the 10W30. I have no idea if running 5W in winter helps anything, as we have to suffer through that garbage called "oxygenated fuels". She was using Falken Ziex 512s (215/65/15) but we just changed her over to a set of '06 Impreza 16" wheels with stock 205/55/16 (I know there's a signicant difference in sidewall) Potenza RE90As. The low point of 20mpg happened just before the swap (along with full suspension swap) and she got a consistent 23.5mpg right away. I realize the overall diameter of the wheel, which can affect the gas mileage (since it raises the final drive ratio), but it's gotta be pretty negligible. Maybe since it'll help her accellerate faster, she'll feel less compulsion to shift at 4K. Yeah right....
Dave, I wish that when the shop was replacing her HGs that they told me her crank pulley was bent but having dumped $100 into a NOS pulley, I can't justify it right now. Unless there's a cheapo ebay pulley that will work well...? And I've told her a million times that if she shifts lower, she'll get better gas mileage, and sometimes she does, sometimes she doesn't. And the fact that our highway mileage is marginally better than mixed makes my argument pretty weak.
As far as I know, the O2 sensor is original. I don't have a CEL (that I'm aware of--I know they "hide" sometimes). How many does this car have--two?

[Mikey97D]

Some people have said on higher mileage vehicles that O2 sensors can get lazy and a loss in mpg is significant. I don't have any data to approve or disapprove of this.

[Huffer]

O2 sensors definitely degrade over time... much like catalytic converters do.

I would replace the O2 sensors if they're more than 5 years old.

[OutbackMat]

The weird thing is that I don't remember the car ever getting very good gas mileage. We got it towards the end of '02 with about 50K on the clock.
Six months later, I bought a '99 2.5GT with a 5MT that had 43K on it and the worst I ever got out of it was 23mpg. I can't remember what the highway mileage was, but I think it was just shy of 30. I just remember thinking that the car always got much better gas mileage than my wife's BG, despite the fact that the BG was supposed to get about the same since it was 90% front drive unless traction was bad.
Could the O2 sensors have been on the way out when we bought it? And are there any good places to get them inexpensively? I imagine they're special order Bosch units.... :roll:

[Huffer]

You can get generic replacement O2 units for around $50 a piece, which you have to cut wires and solder the factory plug onto.

Direct O2 replacements can be had for around $80 each - I will do that next time, it makes replacement that much easier. The worst part is getting the damn sensor out of the pipe, especially with a lot of rust.

I'm vowing to loosen and lube the O2's once a year from now on. :evil:

The other thing to consider is that the BG has a raised road profile, which creates drag underneath the car, and it is also carrying about 100lbs more on the rear wheels because of the hatch, and the glass.
Plus, the 4EAT is at least 50-60lbs heavier than the 5MT.

Which leads me to ask the question - how is it that your wife is shifting at 4000rpm when it's an auto? She should just put it in D and go. Don't manu-shift, you're buggering up the TCU shift logic.

[Mikey97D]

Which leads me to ask the question - how is it that your wife is shifting at 4000rpm when it's an auto? She should just put it in D and go. Don't manu-shift, you're buggering up the TCU shift logic.

Makes me think she's holding it close to the floor everytime she leaves a stop. I'm driving an '00 Outback 4EAT wagon which weighs more than the BG plus a tow hitch on the back and I can get 25+ mpg just by taking it easy on the gas peddle and mine needs a tune-up.

OutbackMat - what tire pressure are you running? I'm running 35 psi on all fours.

[OutbackMat]

I've used the generics before...for the extra $30, I'd get the direct replacements--$80 would make it the cheapest parts I've bought for the car yet! :lol: You don't think a little anti-seize when they go back in will keep 'em loose? I guess when I replace them, I'll hose 'em with PB Blaster for a week. I'm sure the wife will LOVE that.
We dropped the car on '06 9-2x struts/springs, so we're definitely lower, but I know we're missing the steel plate that goes under the engine--do they make a plastic one to help with underbody airflow?
I shouldn't say she "shifts" at 4000, more like she "revs" to 4000 before letting the trans shift. I wouldn't shift something this heavy without a manual valve body, something I doubt exists for this car.
So I'll replace the O2s.
I was also thinking that sticking a straight pipe in place of the accordian tube to the plenum would be a good idea to smooth the airflow to the engine. Maybe that and bypass the TB in the coolant flow. That'll help me actually get cooler air for better intake temps and more efficient combustion.

EDIT: Mikey, we're at 40psi and max is 44 or we're at 38 and max is 41.

[DLC]

I got a recorded 30MPG in a 2008 Impreza hatchback during my vacation. AWD, Automatic, with at least two, and usually three persons in the car at all times.

I also got 28MPG over the last 360 miles in my GT, half city, half 55-65MPH highway and no AC.

I noticed in the Impreza that the mileage was affected severely by the driving style, and that my very smooth driving yielded much better results than my lady's herky-jerky on/off style.

Driving smooth is my biggest suggestion.

Top Gear tested a Prius vs M3 around their track and found that when the Bimmer was simply keeping up with the Toyota, it got BETTER fuel mileage than the Hybrid, with a 400+ BHP V8.

[AJM]

I averaged around 35 in my Bd...but I had a decent mod list, and bd 2.2 5sps are light in the Suabru world.

I'd say a true CAI, lightweight pulleys, and stop reving so damn high, there's no reason for that all the time. slow down to 65-60. Every 5 mph over 60 is a certain percentage lost in fuel economy.