Can anyone please advise, as the G30 has 2 expansion tanks, a larger and a smaller tank, which tank provides cooling for which loop ? My guess is the larger tank is for engine, but could not find this information to confirm.
https://www.realoem.com/bmw/enUS/sho...diagId=17_0988
[EDIT]: Never mind, found this helpful Youtube video.
The larger tank is the only tank with level sensor, so if the iDrive gives the low coolant warning, it is the larger tank needing coolant topup. Secondly, yes I was correct at guessing that the larger expansion tank cools the engine and turbos, so it is pretty critical.