In the last few days the "low coolant" light has been intermittently turning on on my friend's BMW X3 (2007 ~70K miles). The light is not constantly on yet.
I checked the coolant reservoir and float stick was slightly below the "low line". Nevertheless, the float stick was still floating and there was still some fluid left inside the reservoir.
I would be inclined to buy and pour in new coolant, however, after googling around I have few doubts now:
She got engine gasket replaced outside BMW a year ago. Does this kind of job imply also coolant change? if so, then I guess there is possibility that it is not the blue BMW coolant in her car anymore and in this case the coolant should be flushed if its type can't be determined anymore?
If coolant reservoir is not completely empty and low coolant light is turning on only intermittently, is it ok to drive around for a day or so for short trips until this gets properly fixed?
If it is better not to drive around in current condition, can I simply pour in a liter of distilled water to get the car around for a day or so? I guess this would dillute the water:coolant ratio from 50:50 to something like 60:40.
I suppose it is also important to find out why coolant has disappeared. I guess there are three possibilities:
coolant is leaking in oil compartment (in this case the oil may become milky)
the coolant is pouring on the street (in this case there could be something dipping below the car)
coolant gets burned together with fuel and goes out through exhaust pipe (not sure what hints are for this case).
Are the any possible root causes that could explain why coolant disappears?
I am attaching following picture that may provide more hints, because there is fluid exhausted with force from what I think is radiator hose: