Since model year 2004 (and Z4 MY 2003), BMW has been using an engine coolant with a long-term life rating. The long-term antifreeze/coolant must be completely drained and replaced only in conjunction with any Repairs that require replacement of aluminum or metal cooling system components. The corrosion protection for these components is provided only in a new long-term coolant. On all other repairs that involve draining of partial quantities of coolant, replace the drained quantities with new long-term antifreeze/coolant.
BMW recommends filling the cooling system for protection against freezing down to -34°F (-37°C). This means an antifreeze ratio of 50% antifreeze and 50% water. In severely cold areas, the antifreeze can be increased to 60%, which provides freezing protection down to -62°F (-52°C). Do not exceed a 60% ratio of antifreeze. The specified antifreeze ratio is important, since an insufficient amount would impair anti-freezing and corrosion, inhibiting protection. An excessive amount would not improve freezing protection, but would instead reduce freezing protection. At all times, the antifreeze and water should be pre-mixed before pouring into the engine. If pre-mixing is not performed, damage will occur to the water pump assembly.