I talked about the situation here:

http://www.xoutpost.com/bmw-sav-foru...-blew-out.html

the garage I took it to says today that it would not have read hot if all the coolant was gone. I drove for 8 miles at 55 MPH with outside temp of 50. Does the coolant stay in the radiator even if a hose comes off under the expansion tank?