When i saw this thread highlighted in my mailbox under trending m5board posts, I immediately jumped to it. I have much to say about this.
Trizzuth you are right, everything, every word.
I bought a factory delivery bmw E92 M3 in 2013 (4.0 liter S65 engine V8, no turbo, which is the same engine as the E60 M5 s85 V10 minus two less cylinders).
I flew to Munich, germany to take european delivery of the new car in 2013. After only 380 miles on the odometer, having crossed the border to Italy, i first discovered the Idrive message : "Engine oil low ! please add one quart !" I thought it was some kind of fluke but called BMW germany, after being transfered a few times, a german master mechanic told me in broken english to add 1 quart of 10W60 oil which i did after i found a center to get it (with difficulty on a holliday). He said nothing else. This was to become a continuous issue with the car. Back in the states the dealer bullshited as they do, trying to reassure me improvising various random reasons : "oil consumption will stabilise after break in". They started an oil consumption log but soon forgot about it, within months they gave me a blank stare when i would bring the oil consumption issue to them, they gave me free fill ups whenever the car requested oil but they stopped that immediately the day the car went out of warranty. I kept my own log of having to add oil between oil changes over the years.
I have had to add 1 qt oil every 800 - 1500 miles but that is because i mostly drive it on the local freeway. If i take it on the highway on long distances, the oil sensor level will drop from max level to min level in just 4 hours of highway drive and give me the warning. I know from experence now that if i only drove this car on the highway, it would require 1 quart of oil every 350-400 miles, possibly less, just like during my trip in germany.
The oil sensor was a panacea for the dealer to dodge and confuse the engine's oil consumption, they started blaming it. Obviously they know the engine consumes oil since they've drained the oil to measure it when the warning came on (and they put the oil right back into the car, i emailed bmwna if this is normal practice, i was told it is.) After a long highway drive when driving locally the next few days the oil sensor level ifrom the idrive would pop back up to mid level. I seriously suspect that the lack of dipstick design was purposedly done to hide and confuse the true engine oil consumption.
Here i should mention that i've had so many other issues with the car that the oil consumption was forgotten while i had to battle the dealer to do other needed repairs. I eventually gave up having to fight the dealer under warranty for the oil. Eventually in 2017 they gave me a printed document " SI B11 03 13 August 2016 Updated Technical service bulletin" which is an update on oil consumption from BMW that claims that 378 miles per quart (2.5 liters / 1000 miles) is normal for M cars with "S" engines. I believe your M6 has the S63B44T0 twin-turbo 4.4 liter engine.
Here it is important to mention that I know many other M3 owners's through car forums like this one whose car consumes not a drop of oil, neither during breakup or ever. So this is not just a model specific design issue from BMW but also extremely poor Quality Control. I know other companies have been sued and convicted for excessive oil consumption (with much much lower consumption numbers). I am not aware of any lawsuit against BMW but if there is, I am in.