Gentlemen,

What can be done to decrease fuel consumption?

At the time I got my Forester 2005 EJ205 (70k km on the odometer) delivered from Japan, I drove it for 3000km to my city from the port and I measured fuel consumption - it was ~ 9.2L\100km highway only.
That was a year ago. I did not measure fuel consumption after, but It seems that the fuel level gauge arrow goes down fast.

I am thinking about what, in general, could be done to decrease fuel consumption.

As of now:
1. All fluids changed: Engine oil Pennzoil Euro 5w40 (Oil changed every 4-5k km), ATF Subaru, Differential fluid Motul.
2. ECU remapped to 91 Canadian.
3. All filters (except the fuel filter) changed: Automatic Transmission filter, Air filters, and Engine filter for sure.
4. Spark plugs replaced.
5. Red Line injector cleaning fluid used once.
6. Driving style is normal, average, car being used as a family car. No racing or aggressive driving.
7. Tire pressure is normal.

What do you think guys? Please share your thoughts.

Thank you.

 

Only you and your right foot can do anything about this issue.
Subaru flat four? Auto? Nearly 2 decades old with 30 year old technology?

But seriously, this isn't the 1st post here on this subject, and most will reply that if you buy a Subaru, fuel economy should be the last of your concerns.
However, I'll throw my favourite into the ring......fuel injector cleaning at 70/80k miles, as injector spray pattern is crucial with turbos and overlooked as a maintenance issue. Your car will run better and gain lost horses, but you won't notice an economy gain as you'll be enjoying the improvement in performance ¡

 

Things that worsen fuel consumption:

Using fuel with lower calorific value (usually added ethanol).

Lower octane tune so more retarded ignition timing and possible enrichment to prevent knock/detonation.

Driving at speeds where the auto transmission doesn't "lock up" the torque converter.

Lazy coolant thermostat, it may be at operating temperature when stationary, but may drop when driving, especially when using the heater. Do not rely on gauge (its dumbed down), use OBD live data.

Oxygen sensor getting slow to switch/respond; I went for almost a year of driving noticing something was off every now and again with intermittent rich smell from exhaust, before the sensor finally died and logged a fault code.

And my favourite on my cars: The need for a Italian tune up...to burn off all that carbon on the piston crowns and exhaust valves. Additive only do so much. High speed running above 3000rpm for an hour, but not using full throttle (as that causes rich mixture). After that fuel consumption improves until excessive 'normal' city driving causes more carbon build up requiring another blast.

 

@hedgecutter Yes, you are right, the car is old with an engine that was engineered decades ago and its turbo, so it might consume more fuel than modern cars, for sure. I was just thinking what could I do more to try decreasing the fuel consumption, just to try...
@ALi-B Forgot to mention that both O2 sensors were replaced last year, Denso ones were installed. The thermostat was replaced as well, and OEM was installed.
Good point regarding RMPS: I am driving my car in the city mostly and RPMs are always lower than 3000rpm. Summer is coming so I am gonna use my car for driving on highways more (camping, kayaking far from the city). I used Seafoam sprayed in the intake last year and noticed a white smoke during the procedure, so might had a lot of carbon build up. I don't know why, but I am afraid to use that Seafoam spray again. Seemed like the engine was sounding rough at the time Seafoam was sprayed. Not sure if its safe to use Seafoam once in a while.