Flushing the cooling system occasionally can help prevent the formation of aluminium rust inside the cooling system. In order to do this, you should first drain the coolant. Before that, make sure that the engine is not hot. You can drain most of the coolant by opening the radiator drain cock. Do not pour the coolant on the ground and avoid direct contact with the skin. After that, fill up the radiator with water and drain it multiple times. This will help to remove the traces of the old coolant completely. Fill the radiator with fresh coolant afterwards. Now you have to remove all the air that is stuck in the cooling system by bleeding.