I would insert up to a couple of pint or so of distilled water.. any more and I'd get some coolant To combine. if it goes off all over again, carry it for the vendor. its possible just evap lack of the drinking water percentage of the coolant blend. glycol https://stephenhdtlb.blogdun.com/27817253/5-tips-about-types-of-coolant-for-bmw-335i-you-can-use-today