I might increase as much as a few pint or so of distilled water.. anymore and i would pick up some coolant to mix. if it goes off all over again, carry it towards the seller. its very likely just evap loss of the drinking water part of the coolant https://travisaswyr.ezblogz.com/58825561/the-smart-trick-of-types-of-coolant-for-bmw-335i-that-nobody-is-discussing