To me, its very simple physic and not some Houdini playing tricks with our car. The puzzle of mysterious missing engine oil is not difficult to solve, having "played" with cars for more than 20 years, there's only few possibilities. E90 is a little more sophisticated especially the N52 magnesium alloy block which is running a condition based on-demand engine oil pump, so since everyone is experiencing 7k to 8k for 1L top up, I take it as a norm.
We tried to establish the cause and there's quite a few traditional cause like loose piston ring, leaky oil seals, leaky gasket, loose valve seals but the N52 does not show any symptom confirming any of the above which lead to only one possibility ~ evaporation of engine oil.
A super hot BMW engine, paired with the thin 5w-30 engine oil, is a great recipe of "evaporation" of engine oil. Try 5w-40 I believe oil loss will reduce, but same with performance too due to the heavier oil.
On top of that, I think the condition based on-demand oil pump is not helping too. I saw the oil pump is a chain driven pump connected to the crank shaft, yet there's a regulator to regulate the quantity of oil going to the head, why? Izzit something to do with the hydraulic lifters? Next thing to find out is how the oil pressure regulator works and what's the condition.. care to join me for the quest of this piece of jigsaw to complete the oil loss puzzle?!
And I'm not even running an N52..
My N46 4-potter aluminum alloy block also has oil loss problem but less serious compare to the N52.
I will be testing out the Castrol SLX 0w-30 in my next change, no LL label..
but claim no oil loss, for the name of science!
BTW, I saw "Engine oil level OK" in the above iDrive reading. So no problem ma..
I wonder when they will show the oil color on the iDrive screen..