On my 2015 CC with a Unitronic Stage 1 tune, I use Mobil1 Euro 5w-40. I sent a sample to Blackstone at ~7200 miles and they said I had plenty left. I change at 8500.
I had the same issue in my 2016 Sportwagen at ~120k miles, oil changed every 5k. Based upon my web sleuthing, there IS an issue with 2015 and earlier 1.8 engines and oil consumption. Something about a bad ring design. My car was using upwards of 1qt per 800/1000 miles depending on the amount of highway driving. No oil spots on driveway, no blue smoke at startup or any throttle application or not. I DID have a "damp" appearing spot on the bottom inside of the tailpipe and black speckles/dirt on the tailgate. Mechanic told me that the catalytic converter can hide a significant amount of oil use. I tried an oil flush (two) and did not notice an appreciable change, and was quoted upwards of $10k for just an engine. There is a BG flush kit, sold to "professionals only", that is upwards of $250 on the big online retailer site- comes with what looks like 2 gallons of stuff. I did not use this, and the shop I have the work usually performed at refused to do it (I understand their reasons). As a "Hail Mary", I did the following: Parked it on ramps. Pulled the plugs- Number 2 was obviously the problem. You should pull your plugs and look at them. Cut a piece of 1/4" OD copper tubing long enough to get into the cylinder, and put a little bend at the end of it Previously ordered GM "Top Engine Cleaner" and Ballistol (primarily used as a weapon cleaner, but non toxic). Looked into cylinders with a borescope. Yup, #2 was the worst. Liberally sprayed the GM cleaner through the copper line into the cylinders. It foams, so you can hear it fill up. Turned engine over by hand with a socket and ratchet. Sprayed some more. Waited, then sprayed Ballistol in there. Turned engine over by hand. Sprayed some more. Repeated the process a few times a day, for 3 days. Looked into cylinders again and saw carbon removal from top of piston. Before start, sucked out excess fluid from the tops of the cylinders with a Harbor Freight brake bleeder. Installed new plugs. Drained oil where it sat. Installed new oil and filter, plus BG oil flush, ran at idle for 30 minutes (warm-up, plus 15 minutes). Changed oil and filter again, using Mobil 5W40 Euro oil. Problem appeared worse after checking oil after ~250 miles of highway driving. Was not happy. Waited it out (nothing to lose), and saw oil consumption decrease over time. Added about 1.5 qt in total over 3k miles. Changed the oil again, and have almost no change on the dipstick after 1k miles. So, I got lucky, and the problem is fixed. I have not taken the time to pull #2 plug and look again at it or the piston top, but in any event, oil consumption is WAY down. No more "damp" tailpipe and if there is black fuzz on the tailgate, it is much finer and harder to see. I am also using Top Tier fuel and have added a couple of cans of Gumout cleaner with PEA. I have noticed a significant improvement in idle quality with these things. Not sure if I will go to 3k oil changes, as obviously 5k was not working. I do NOT idle the car much at all outside of driving/traffic (no sitting with the car running needlessly).
Usually, motor oil goes bad because the additive packs that are in the oil get burned off or used up. I'd imagine that this new Mobil1 Annual Performance has more additive packs than what standard Mobil1 has but it's probably able to go that far because you're going to have to add additional oil that gets burned off because every car burns oil.
