I have a 1984 BMW 318i and recently steam has been coming out from under my radiator cap.?

I have a 1984 BMW 318i and recently steam has been coming out from under my radiator cap. Besides the obvious, is there another cause that would trigger this?I have a 1984 BMW 318i and recently steam has been coming out from under my radiator cap.?replace the cap . and watch the Temperature if it is running over 190 change the thermostat and flush the cooling system..I have a 1984 BMW 318i and recently steam has been coming out from under my radiator cap.?Let the BMW people look at it.