325i Overheating

I'm not an expert or anything but I had the same trouble a few months ago. I found out that I was not leaking any fluid anywhere and there was no water or antifreeze showing up in the oil when I checked it. I haven't had the car long so when I replaced the thermostat and water pump and refilled the radiator the holding tank was showing that it was full. After running it a little while it was still overheating. After researching I found out that the screw on top of the radiator was a bleeding screw that allowed the radiator to fill properly. Once I took the screw out and took the radiator cap off, I discovered that the car did not have enough fluid in it. Once I bled the radiator properly, I had no more smoking and no more overheating. I hope this helps.