I'd personally insert as many as a couple of pint or so of distilled water.. any more and I'd personally pick up some coolant To combine. if it goes off again, carry it to your dealer. its probable just evap loss of the water portion of the coolant blend. glycol https://mylesqmwyz.bloggactif.com/27862501/5-simple-techniques-for-types-of-coolant-for-bmw-335i