Hack Mechanic: I own and drive a BMW 525i, a 2005 model, E51. I am having a recurrent problem of the coolant in the tank drying up. I work rotational assignment in the offshore oil industry and so I am away from home for 28 days, every other month. No one drives the car while I am at work for 28 days and when I return home, I notice each time I start the car upon my return, the coolant in the tank has dried up completely. There is no sign of a leakage. I don't know what may be causing this problem. Can you help?