Hmmm, my mechanic at M1 recommends not to use BMW coolant due to it's antifreeze properties (only for colder climates). It tends to clog up the radiator over time. However, like bro Mtigo above I also use Toyota Long Life coolant as it helps increase the boiling point of water without the pressure build up. This helps cooling more effectively. In addition to that, the coolant (with proper ratio) is also supposed to help prevent corrosion.