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Sudden excess fuel useage

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Hi Guys, my 2003 2.5L Outback highway fuel mileage has jumped from approx. 8L/100Kl to 9.8-10L/100k. Air filter cleaned (K&N), new Iridium plugs, exhaust system clear, running just fine except for this sudden fuel use increase. Not much hair left, pulled most of it out!
Help, John R
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06 3.0R JDM facelift SI Drive-shift paddles. 87 Brumby EA81 (Brat) 4MT D/R
609 Posts
Here's a link of a recent discussion on fuel consumption

Edit - 8 L/100km is really good (previous car 01 MT outback - best it ever did was up to 8.4 L/100km on a long flattish trip in ideal conditions.

Average mixed running 65% highway / 35% short running - got 9 - 10 L/100km - is still ok.

Guessing you've checked other obvious stuff like tyre pressures, dragging brakes, wind resistance from roof racks, extra weight, speed etc etc

Could be rouge sensor perhaps not throwing a code.

Another thing perhaps worth doing /trying is using some upper cylinder spray foam cleaner ( spray into throttle body) ( did this with my 2.5 and it helped)

And a bottle of injector cleaner in tank.

Perhaps it just needs a good long continuous run.

Edit 2 - Does anyone else drive the car? Their different way of driving may affect the ECU (it re leanns from the change in driving style) so perhaps this may affect fuel consumption.

MY17 Outback Diesel Premium
83 Posts
I was getting in the high 7's per 100 km when I had my 2.5 manual Outback, but that was most doing 90 km/hr or so, not 110 km/hr. (I am achieving high 5's per 100 km with the diesel manual doing the same run).

What RPM did you normal cruise at and what RPM are you cruising at now?

Are you an automatic transmission or manual?

If automatic: check the transmission fluid levels and check for slipping bands etc.
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