[wdb]

The purpose of this FAQ is to collect and present information relating to the STi and fuel consumption. With a car like the STi there must be at least two main considerations when discussing fuel; mileage and performance. This FAQ will attempt to present and address them both as completely as possible.

Even though the STi gets pretty darn good mileage considering its performance, it will never be an economical car -- for a whole lot of reasons besides the amount of fuel it uses. So forget about finding "how to get 35 MPG from your STi!!!" What you will find is the collective knowledge and experience of contributors on this forum as it relates to the STi's fuel, mileage, and performance. The more we know about this topic -- all aspects of it -- the smarter we can all spend our petroleum dollars, and the more we can enjoy our cars.

Comments and ideas are always welcome.

Gas Mileage - General Information

• A well-tuned car gets better mileage
• Up to a point, higher tire pressure = better mileage (and, up to a point, better handling). Suggested pressures are 40 lbs. all around, 40F/36R, 36lbs all around.
• Be prepared for even worse mileage when the TERRIBLE oxygenated gas hits the pumps from Oct - Feb.
• Driving slower on the highway improves mileage, up to a point. It may be better to keep the car in a range of 3K to 3500 RPM for optimum fuel mileage. (Anyone remember the national 55 MPH speed limit?)
• If you do a lot of stop and go driving weight and drivetrain intertia are the enemy. Subarus in general have a reputation for low gas mileage in 'city' driving conditions.
• Shift at lower RPM's, for example between 3000-3500 RPM, to improve mileage.
• Try a SKIP-SHIFT technique in normal driving; 1-2-4-5 (skip 3rd gear) recommended for the best combination of fuel savings and practicality.
• Turn off cruise control on hilly highways and control throttle so as to keep from going on boost (you'll need a boost gauge for this). Reported 2MPG improvement by doing this versus letting cruise control maintain steady speed.
• Momentum is key. Maintain speed, try to stay away from braking, turn smoothly and only as much as needed.
• For highway/freeway cruising, try setting DCCD to manual/full rear (open); reports vary but some people see 3 MPG greater mileage. This is a no-cost "mod" anyone can try.

Reported Mileage

• trip - 26.2 MPG: stock STi, 90%/10% hwy/city, 94deg/humid, AC on
• trip - 26 MPG: 700-mile road trip; hilly terrain, cruise control at 85 (flow of traffic)
• worst - 10 MPG: (estimated); maniac driving spree down favorite <strike>backroads</strike> closed course
• worst - 3 MPG: during Texas Mile high speed run (and proud of it)
• worst - 7.5 MPG: hot lapping Streets of Willow
• worst - 6.2 MPG: at Roebling Road
• avg - 24-25 MPG: 50% highway at 75, the rest rural at 40 to 50 mph
• avg - 18 MPG: rarely drive fast (no other details)
• avg - 21.5 MPG: 65% highway 35% city, stay off the boost unless provoked
• avg - 23 MPG: city and 27 or 28 MPG highway
• avg - 17-18 MPG: during break-in miles on '05
• avg - 17-18 MPG: a lot of traffic lights, stop-and-go driving (2 reports)
• avg - 21-22 MPG: highway with stop-and-go construction traffic, 26 if things are going smooth
• avg - 20 MPG: daily-driver mileage, commute is almost entirely highway, offset by spending 70% of time idling in city traffic

Performance - General Information

• Lower restriction exhaust = better performance and better efficiency
• With all variables equal, a lighter STi will consume less gas than a heavier STi

Specific Mods and Mileage

• No difference noticed when going from stock to Cobb AP Stage I
• No difference noticed with V-Limited front lip
• Better overall gas milage by going to a bigger turbo
• Carbon fiber driveshaft improved gas mileage an average of 1-2 MPG (2 reports)
• Roughly 2 MPG improvement in highway mileage by changing rear wing to WRX spoiler / no spoiler (2 reports)
• At least 2 MPG improvement by going catless
• Cobb AP Stage 2 version 1.05 91 oct - never lower than 20mpg with spirited city driving, hwy mileage is usually 5+ mpg better
• Cobb AP "economy map" for STi - results vary but it appears to make little difference in overall mileage
• Switching DCCD to manual/full rear (open) on long highway drives - reports vary but some see consistent 3 MPG greater mileage - this is a no-cost "mod" anyone can try

[91TB78]

Oil viscosity helps play a part in mileage. I got nearly 27mpg on the highway from Tucson to the FL panhandle and my car started with less than 1K miles on it. I had broken it in per Motoman's method and so it was on it's second change of 5W-30 dino oil. I then switched to 10W-40 Amsoil and my mileage went down a little bit. Just a little help..

[CGMDan]

I have found that my STi gets the best gas milage if I keep the rpms around 3-3500rpm. Irregardless of which gear I'm in. At 3250rpm in 6th that means I'm driving at 80mph. If i'm at 55 I'm usually in 5th. Lugging my car at 55mph in 6th has actually gotten me Worse milage. I'll usually average 18mpg in city driving and on the freeway I'm usually getting 26 or so. I just did my normal 200mi highway run with the A/C off and found it didn't effect my fuel economy. On the track I'll go thru half a tank in 20 min with the A/C on, 1/4 to 1/3 when off.
When I first got my STi I would skip gears and after a month or so I went back to rowing all the gears and found it didn't make any difference.

One thing I would add to the list is, when possible on the highway use cruise control. It helps smooth out and eliminate unnessesary throttle inputs.

BTW I'm averaging just over 2K mi a month. And I usually have to fill my tank every other day.

[SQB-D00]

Consider this if you would -- Internet hype or fuel shortage hope? "Acetone In Fuel Said to Increase Mileage; Readily-available chemical added to gas tank in small proportion improves the fuel's ability to vaporize completely by reducing the surface tension that inhibits vaporization of some fuel droplets." Complete article may be found at:http://pesn.com/2005/03/17/6900069_Acetone/

[wdb]

Added a few more mileage reports (all in the "worst" category, heheh) and notes about running DCCD in manual/full rear for highway runs.

[EyehOO]

with 800 miles on the car (still breaking in) I olny get 16 MPG city(50%)/highway(50%). I can't seem to get much better. I even tried driving like grandma for a fillup, it went to 17MPG and was pure torture. They claim 18/24, is my car sucking up more fuel than it should for 800 miles?

[91TB78]

What was so odd that during a cross-country 1600 mile trip, I got better gas mileage at around 85+mph. I've tried driving slower and lower revs and I get worse mileage.

[WRX_XB9R]

I agree that higher highway speeds lead to better fuel mileage. I was able to get 26+ mpg on a 85mph average closed course test. I just did a 70-75 mph highway run in MO and KS and got 24 mpg. A 50/50 mix city/ highway got 20. My normal 3 mile commute neted 16.7 and 16.9. The one tank test of the economy map on my normal commute netted 17.5.

The 26+ was at stock. The rest except econ were at custom mapped stage2.

[JDSTi]

Just wanted to add some trip records I've had. Since getting my ScanGauge, I've recorded my mileage on road trips (when driving with the wife). We do a 50 mile commute from Tustin, CA to Monrovia, CA every other weekend, and I just got back averaging 28.8 MPG for the trip (90% freeway, 10% city). I'm not sure, but I think this may be an STi record for the best trip MPG. I drove mostly 75mph on the freeway, but did use almost every trick in this FAQ (my car is stock). I haven't yet tried messing with the DCCD, but if that does work I could be seeing 30 mpg?!?!?

Also note this was with 2 people in the car, and 100 lbs of luggage, and using the winter gas (which is reported to be bad for good mileage).

Anyone out there done better?

-JDSTi

[wdb]

Originally Posted by JDSTi

We do a 50 mile commute from Tustin, CA to Monrovia, CA every other weekend, and I just got back averaging 28.8 MPG for the trip (90% freeway, 10% city). I'm not sure, but I think this may be an STi record for the best trip MPG.

Could be. Is that 50 miles round trip, or 50 miles one way / 100 miles total? Either way, at 28.8 MPG you only used 2 to 4 gallons; at that level, a lot of variables could affect your MPG number.

Thanks for sharing and please do keep us updated.

[JDSTi]

It's 50 miles one way, but I'm using the ScanGauge to find my mpg which is very accurate (since it gets the info directly from the OBDII port).

-JDSTi

[wdb]

I added the SKIP-SHIFT technique to the top post, based on information collected by chrismindless and discussed in this thread.

[kb2spn]

I made a 490 mile trip to Toronto Canada.I cruised a 75 mph,slowed a few times because of construction.I filled the tank once at the border,I dont recall the exact milage but it was over 400 miles.I will be making the trip in the spring again,this time I will record every detail.

[UltimateLurker]

Observation.

With 980 miles on my bone stock '05 STi, I made an 80 mile Interstate road-trip and got 25 mpg. I gave it a little stick coming out of the gas station, and had to slow a few times for traffic, and give it a little boost to get back up to speed, but other than that, I left the cruise control on.

I did the very same thing in my bone stock '05 WRX and got 23 mpg.

[wdb]

Don't worry, once you get past the 1000 mile mark your mileage will go right into the toilet like the rest of us.