I drive a 2013 Smart Fortwo pure and it is mysteriously losing coolant. When I drive the 10 miles from home to work it goes from the max to minimum line in the reservoir. It has overheated once and completely ran out of coolant once. I had a faulty radiator fan fixed on it a year ago. I’ve had two places look for leaks and they cannot find one after running extensive pressure testing. I’ve also had it checked for a blown head gasket and it doesn’t have one. I’m completely at a loss. Any ideas?