I haven't topped it off since the expansion tank split. I am trying to figure out if I need to order just the expansion tank and coolant or if i need a water pump too right away. The car is definitely low on coolant, but it really only lost what was in the expansion tank. Maybe 2 quarts?

It's too cold here in PA to just put straight water in to test it, and I don't really want to put anything other than BMW coolant in it either...