Cooling fan:( on 2000 BMW 323Ci

my cooling fan light keeps coming on and off. And sometimes the temperature hand passed normal and hit red. And now i can hear a whistling sound in the back of my car. It's scary!!! I took it in to do a full body check but the guy at the gas station just put water in my car and that was it. Nothing was solved. I dont know what to do because im trying to avoid going to a mechanic cus last time I went, I spend almost a thousand dollars :(

Asked by for the 2000 BMW 323Ci
sounds like you have a leak somwhere have the cooling system pressure tested