I have had an increased gas consumption issue with my outback 2010 for many months.

Have they checked the engine compression? Maybe your car is just getting old.

Is the car running cool or at normal temperature? Running cold will increase fuel consumption.

Hi F_O_R: I appreciate the answers. The car has been running at normal temperature environment (Bay Area/ SF Peninsula) for all its life before and after the increase in consumption. I will address about the engine compression. I am kind of think it might be computer things that control the engine/injection. but again i m not sure. It's interesting you mentioned the car 'might' be old at 75,000 miles for 2010. But a dealer shop representative said similar. That is up to Subaru Manufacturer then. My previous car was second hand Wagon Legacy 1994 and its engine performance never dropped through 9 years of driving until I donated it at 240k miles.

I re-read your last post. I was not talking about the temperature environment that you drive in but the operating temperature of the engine. A faulty thermostat could make the car run cool and cause it to run in a richer start up mode.

FOR, you're unfortunately off on this one, as t-stats are remarkably robust on Subies. Best guess here is a slipping CVT that's wasting gas.

I understand Ernie but it is a possibility that can be confirmed by checking the operating temperature.

Yup, but this scenario would only realistically occur if someone REMOVED the thermostat. Hope their CVT is ok....

Slightly off topic, I had a Ford Explorer that was thirsty and heater was marginal in cold weather. New thermostat fixed problem.

Again, bad OE t-stats are non-existent in Subarus for decades.

So far, I went to three shops two of which are Subaru Authorized shops. None of them knows what s wrong. Before the check engine light came on, i got about 380 miles per full gas tank for driving around the city including on freeway and local street. After that check engine light till now I got only 330 mile per tank. The gauge or measurement seem consistent with what i experience when speeding: unable to push ny car faster while rpm goes higher and engine got louder. The last shop which is local shop checked all parts and found nothing wrong so only way to try is to reset the computer. But nothing improved.

Change your CVT fluid and hope for the best. I fear you have a failing 9 tr old Phase 1 CVT.

I replaced transmission fluid. Consumption and power not improved.

Just for due diligence, have you ever replaced the original platinum plugs on your '10? The new iridium ones, unlike the OE plats, are incredibly durable, nit blowing off their anode tips after 4-6 years. I'm not sure that running a consequent double-sized gap would reduce efficiency that much, but I wouldn't doubt it. You of course could put in cheap copper or plats again if your life with this aging chariot is getting short. Iridiums are down to $30/set online, so there's a bargain there, and maybe worth a shot. Note that blown-off anodes on the plats will NOT signal a CEL, so it's a good idea to check...even though that #4 is a pain to reach.