I have a 1997 BMW 318i and I was driving in traffic and because my fan was unhooked the car overheated and blew a hole in my radiator so I replaced it. Now as soon as I start the car pressure builds in the radiator and it keeps building. On top of the radiator there is a cap to unscrew to bleed the air and when i open it steam comes out non stop. The heat also doesn't work. Any insight?

Thanks