I'd personally incorporate approximately a couple of pint or so of distilled drinking water.. any more and i would pick up some coolant To combine. if it goes off yet again, bring it on the seller. its probably just evap loss of the water part of the coolant combine. glycol https://manuelqafnt.blogars.com/26817558/the-5-second-trick-for-types-of-coolant-for-bmw-335i