http://www.bmwe34.net/e34main/trouble/overheating.htm
This will help you understand the issues and work through you diagnosis or at least be conversant when you talk to the mechanic. A big part of figuring it out has to do with whether it overheats on the open road, just in stop and go traffic, or when you have turned it off and turn it back on before it has fully cooled.
A piece of friendly advice. Don't drive it until you get it fixed. Overheating fries lots of other stuff and the cost of repairing can go up substantially it you let it happen again. With that said, it is a really common problem. Every other post in June was related to overheating.
And welcome to this board. Your name looks like you might be a girl. As far as I know, I am the only girl active on this board, so I hope you are a girl. If you are not, welcome anyway.
Dinan chip, Bilstein sports w H&R, RD sways, RD strut brace, 750 bushings, Zimmermans/MetalMasters, O.E. M Pars, Eisenmann muffler