Car: 2000 Outback wagon (2.5L, auto)
Miles: ~94,000
Last week Thursday (8/31) I had the dealer perform:
*Coolant flush/fill
*New fuel filter (though seeing the instructions on this site I could have saved myself ~$25 and done it myself!)
Friday after work I fill the tank, then drive my 35 miles home.
Saturday 9/2 I drove it about 60-70 miles.
Then Sunday (9/3) I changed the plugs to the ones the book listed (NGK BKR6E-11 V-power) and the NGK as was recommended here. Bit of oil in each one (I'll get to the seals at another point in time), one of them a bit more than the others.
When changing the plugs I removed the washer reservoir and the air intake (up to the elbow at the cleaner element compartment, which I left in place). Pretty sure I put it all back right--I know when I had my air filter checked at Jiffy Lube (don't shoot me) they didn't put the filter compartment back together right and I was having some noise on acceleration, but that's not the case here.
Since I had driven the car earlier (30 miles?) I let it sit for several hours (3-4) to cool before removing the plugs. During this time I did yard work and hand cleaned the engine compartment and components with a damp cloth.
I also started to disconnect the battery (negative first) so I could clean under/around it but it sparked once or twice while I was loosening the bolt so I said "Screw it" and just left it in place.
Monday 9/4 I didn't drive it much, maybe 10-12 miles (lazy day!).
Yesterday I drove about 80-85 miles total.
So last night on the way home I notice my gas gauge is dropping a bit fast, and the mileage on the trip meter only read about 120 miles but I was below half a tank.... I usually get 340 on a tank. I just put 11 gallons in it this morning, for 165 total miles (according to the resetable trip meter), which isn't right. I know I didn't reset it immediately after getting gas, but I'm pretty sure I didn't drive 100+ miles before resetting it.
I'm heading on a 145 mile (each way) trip tomorrow, doing some tooling around, then 145 miles back. Normally I could do this on one tank but I'm not so sure now. There's no CEL on and the car drives as usual.
I guess I'll find out how this fresh tank does since I know I reset the trip meter, but wanted to know if anyone had any ideas as to what this might be? Adding up my mileage it's close to 200, and I had about a quarter tank left.... so it's a bit short of what it should be. Would an issue with new plugs cause that? The spark from the negative terminal? Is there a reset I should do (removing the battery power completely) before I leave to let it all reset to 0?
If it happens when I'm gone, I'll take it to the dealer but I'd rather not worry about it, obviously! I thought maybe it was the fuel sender unit but since the gauge was reading accurately (based on my fill up this morning), I don't think it's that.
I'll pick up a new air filter today, but don't think that can be the cause of it that drastically nearly overnight.
Thanks!