A Quest for 35mpg (Subaru Outback Limited Sedan 2.5L auto)

[Zerohour]

Ultra Gauge arrived today. So far so good. Worked like a charm. I've got alot of messing to do with the gauge. Trying to figure out what is the best combination. Also need to work out a "installed" mount. Very happy with my purchase and was easy to use out of the box.

And if the gauge is moderately correct, I should try to maintain 45-50 up my hills instead of 35s. Kinda interesting, but I think the Subaru does better in 4th at faster speeds than slower speeds in 3rd. I need more testing and better calibration to be sure.

[Zerohour]

Things I learned today using the UG:

Subaru runs higher MPGs at 55 than at 45 (~2-4 mpg difference, hard to tell no properly calibrated yet).

Subaru is incapable of using less than 1.6 gal/hr of fuel while accelerating from a stop. Anywhere above 10-12% throttle goes over 2.0 gal/hr immediately. Under moderate acceleration goes to 4-5 gal/hr, which is down to 4-5mpg. Which explains why how I drove last year was causing 21-22mpg and down to the record low of 17.7 mpg. The cold subaru + AWD + Slush Box just consumes fuel like a mad man.

I believe I need to start going after some weight reduction which should help with acceleration.

[d0sitmatr]

good post

what is the curb weight of your scooby ?
I still say the best gains your ever going to see is a re-gearing of the final drive.
from what you just posted, sort of confirms what I believed about my car, there is a point where the intake/throttle body opens wide and starts sucking gas, and that point is in the very low rpm range.
what does have me wondering though, is the difference between ATX and MTX. I could drive 55mph all day long and it wouldnt be much of a difference over 45mph.
my biggest noticeable difference would be any time my RPM registered above 2.9k, once it his the 3k mark I swear I could almost watch the needle drop....

[Zerohour]

Well the thing with the DOHC 2.5 is that the power/torque is pretty much level from 2300 rpm to 4000 rpm. So the motor doesn't produce any more or less power, the rpm relation is just a matter of speed. And more speed with a lean of the air goingin the engine works great on the highway because you can vary with traffic and retain approx same FE, but it still has too low of FE.

I'm wondering how the internals look, and if it would be possible to switch over to a different gear set. I would be concerned about making the gears too long, because the outback is pretty underpowered as an awd sedan. It might actually increase FE by going to taller gear due to the slower acceleration. Truthfully what it needs is a 5th gear. It would then be able to accelerate to shift before 2500 rpm.

I'm starting to wonder if maybe I should have just gotten a pickup truck with 4wd.

But right now it looks like i'm stuck at 25.5's for mileage. That will probably go down a bit more as the weather gets worse.

I need some more ideas to figure out how to get more economy out of the car!!!

Current ideas/projects:
-Mirrors, swapping both over to a Ford Contour mirror with a smaller cross-section. This is going to take some time, fitting the mirror has become a ***** of a project. It might be easier to find two subaru mirror bases, and mount the other mirrors to those. Currently I'm trying to convert the Ford base to the Subaru door.
-LED lights - driving in winter and on 10 hour shifts, I don't see the sun. I could reduce the load on the alternator by 6amps by swapping to led bulbs. But the cost is ~$65. Which doesn't ever have a pay back, and could be put towards another project.
-Weight reduction - currently removed spare, jack, hold downs, and trunk carpet. I don't know what else I can remove without starting to sacrifice the interior looks of the car (and potentially rendering the modifications as irreversible. I would love to try racing seats for the front, but the seats are wired into the side airbags. Removing these disables the airbag system.
-partial upper grill block. Its winter, so might be able to block off the upper grill slightly now.
-heat ducting - I thought about purchasing copper tubing and trying to draw heat from the exhaust header up to the air intake. I'm just not sure if this would work.
-switching to mobile 1, 0w-30 full synthetic - currently using a 5w-30 synthetic blend.
-air cowls on roof. Water shows the truth, the rear window does not large amount of air flowing over top. water stays in the middle of the window. some small shark fins may put air over the car instead of around the sides.
-Kammback, almost impossible on a sedan, and car would have to come out of service during the build. Which I cannot do 1) because its freakin cold 2) no other mode of transport for work commute.
-I'm tried looking for wheels, but it doesn't seem like I could feasible come up with a skinnier tire/wheel combo in a cost effective manner. I would easily drop down to a 195/205 tire from the 225, but I cannot find a rim/tire combo that could be close to cost effective and still fit. I need a minimum of a 16" wheel due to Suby brakes.
-exhaust header not sure if a boost in power would really help the FE. It might on the highway, but my commute is more stop/go and hill acceleration issues.

[Weather Spotter]

Hid's might be cheaper then LED lights.

A Kammback can be built on a Saturday and does not have to take the car out of service. i did mine over 2 days but I could have driven it in 10 min if needed.

A grill block is a must. Try it and watch the temps. You will be surprised how much you can block. I have 75% blocked until ambient temps are over 54 F.

[Zerohour]

I have the lower grill blocked. Now with the UG I can monitor the engine temp more accurately. I was watching it in traffic today. 42 degrees F outside. At idle in traffic after driving a distance to warm the engine: Intake 79-81 to 87-91, engine 185.5 to 186.9. Pretty sure I can venture to block the upper half of my grill. I didn't want to get to crazy and have the fans run all the time.

I really think the killer to the gas mileage is the engine size and AWD. lol Now that being said, I have my UG fairly well dialed down. Might be off by a few percent, but its going to be off by a few percent no matter what as the Subaru has a MAP sensor. My cruising, 60mph speed, on level ground (about as level as PA gets) seems to be 38MPG!

It makes me sad that I don't have more highway to run. My commuter is killer to the FE. Its alot of stops and hills, and alot of idiots in traffic that cause backups. Its worse now that it is dark out. Apparently its alot harder to drive when the sun goes away *shrugs*.

I also installed a forward air block in the engine compartment (part of a mud-flap type rubber). I can't for the life of me remember the air intake temps at similar temperatures, but I remember seeing alot of 50's 60's and 70's since I got the UG. I know its make an improvement somewhat. More needs to be done, but between work/job hunting/ holidays, I might go mad first if I keep trying to on more projects. :-(

I just need free money for a year and I'd be set to go do my own thing! lol

[redpoint5]

Originally Posted by Zerohour

I'm wondering how the internals look, and if it would be possible to switch over to a different gear set. I would be concerned about making the gears too long, because the outback is pretty underpowered as an awd sedan. It might actually increase FE by going to taller gear due to the slower acceleration. Truthfully what it needs is a 5th gear. It would then be able to accelerate to shift before 2500 rpm.

I'm starting to wonder if maybe I should have just gotten a pickup truck with 4wd.

But right now it looks like i'm stuck at 25.5's for mileage. That will probably go down a bit more as the weather gets worse.

I need some more ideas to figure out how to get more economy out of the car!!!

-LED lights - driving in winter and on 10 hour shifts, I don't see the sun. I could reduce the load on the alternator by 6amps by swapping to led bulbs.
-Weight reduction - currently removed spare, jack, hold downs, and trunk carpet. I don't know what else I can remove without starting to sacrifice the interior looks of the car (and potentially rendering the modifications as irreversible. I would love to try racing seats for the front, but the seats are wired into the side airbags. Removing these disables the airbag system.
-partial upper grill block. Its winter, so might be able to block off the upper grill slightly now.

I wouldn't go with taller gears unless you have a lot of patience. The autos are very sluggish as it is.

What you need is a Legacy manual. I got my Su with 120,000 miles on the OD and she gave me 27mpg right away. At 220,000 miles Su was drinking a quart of oil every 2000 miles, but I refined my driving to get 30mpg. That was with no mods and accelerating pretty briskly. Really the only thing I was doing for FE was timing lights and traffic, and coasting every opportunity I got.

I bought a 2007 auto Outback and couldn't stand the sluggish acceleration, terrible mileage (23) and unsteady cornering. A month later I sold her and kept driving ugly Su (the Legacy). What I'm really getting at is that the best idea for more FE is a different car, and then add all of your sweet mods.

I can't imagine lower draw lights would help FE very much, but if you do it then I'd be curious to see your measured results. Weight reduction never translated into better FE for me, but then again I wasn't doing a lot of stop and go. I'd keep the spare and jack, but then again I was rallying the heck out of my ride and probably used the spare on half a dozen occasions.

Originally Posted by Weather Spotter

Hid's might be cheaper then LED lights.

A grill block is a must. Try it and watch the temps. You will be surprised how much you can block. I have 75% blocked until ambient temps are over 54 F.

Agree with the HID's. I would do that just to get better night visibility, if you can keep from blinding oncoming drivers. Ebay has 'em dirt cheap these days.

I'm wondering if watching your coolant temp is sufficient when doing a grill block? Is it absolutely necessary to measure engine temp instead? Guess I'll have to break down and buy a scan gauge soon.

WS- How significant was the improvement in your FE after the grill block? My TSX already has a ridiculously low Cd, so I wonder what I can expect to gain.

[Zerohour]

It's not possible to use HID lights in the low beams of the subaru. The low beam is run on a low current for the day time running lights. This would absolutely screw with a ballast designed to use the 12v 55w for a normal bulb.

I can run the low beams at low current (35w) circuit doing such. Theres not much to get gain on the headlights unless they are completely gutted, re-housed, and re-wired into the car. And for the cost and time, led lights would be cheaper...

Subaru's FE vary from every model. An outback is not an outback is not an outback. Everyone one of them varies. The same years even have LSD's/no LSD's, some have different gear ratios, different engine displacement, different tire sizes, different brakes. and year to year have different emissions, different alternators, DOHC/SOHC. Its hard to compare.

I'm going to try to do some intake changes to see if I can reduce air flow into the intake at lower throttle positions. I can take my vacuum gauge to zero at less than 25% throttle. Its not so much fuel hungry as the engine is air greedy.

[dennyt]

Originally Posted by Zerohour

I'm going to try to do some intake changes to see if I can reduce air flow into the intake at lower throttle positions. I can take my vacuum gauge to zero at less than 25% throttle. Its not so much fuel hungry as the engine is air greedy.

Um... no.

Your throttle plate is sized by the maximum rated power of the engine - floored at 6500 rpm, let's say. Under light load or at low RPMs, the volume of air going through the engine is much lower, say 10% of the max power case. So, naturally, a ~10% throttle opening will give you full pressure (zero vacuum) at low RPM.

You could work on a non-linear throttle mechanism if you want better control of the first half of throttle opening. But getting zero vacuum at low throttle openings at low RPM is just the nature of a throttle plate.

[Weather Spotter]

see if you can disable the DRL "feature". On my car it was one wire to snip and no more DRL's