Q&A

You should be able to add coolant into the radiator. There is an easily accessible cap. If you are still having problems, I would strongly recommend visiting a BMW shop. You don't want to mess around with cooling system problems on a BMW, as if problems exist or persist, you could create massively expensive repairs.

You might also check the lower coolent temp sensor. I had the same problem and kept adding coolent while looking for the leak. The gasket on the sensor goes bad and it just drips a little at a time till it gets hot then stops. Its only 23 bucks and took 5 min to change