Before heading out on a 2+ week, 5000 road trip, I brought my 2016 Forester (50k miles at the time) in for new brakes, an oil change and an inspection for anything else that might need to be looked at. The inspection did not turn up anything. A couple hundred miles into the trip my gas mileage went from 27 steadily down to around 12. On a hunch, I filled with premium gas and that issue cleared right up. After a couple tanks of premium, returning to regular, MPG stayed at 27. Is it safe to assume I just needed to run some good stuff through it to clean out the fuel injectors? And that it was just bad timing that it happened on the trip?
No other problems with the car during the trip. I checked the oil on our last fill up before arriving home and all was good. A week or 2 later (after driving 200 miles tops since returning home), my engine oil light (low oil not oil pressure) came on and when I checked levels, it was bone dry, so I topped it off and called my mechanic. He told me that unless there's a check engine light on, which there isn't, there's not much he can do... but "bring it in anyway. we'll run some codes".
I know that some of that year's Foresters have had issues with burning oil, but this is the absolute first we've seen of it, which also struck me as weird.
My actual question is
Should I just get an oil change and run premium through the car every couple of tanks and skip the mechanic, saving myself a couple hundred bucks for him to tell me they couldn't find anything? Or despite his statement about the check engine light, might there be something he can find?