How long ago was the pump changed? If its more than 3 years its time to drain the system and put fresh. Coolant will get acidic and eat away at metal and won't protect as intended. You can use BMW or Fuches blue, zerex g05 or g48 if you want to stay in BMW's specs. You want to drain all the old fluid so that means pulling the block drain which is above the front o2 sensor. Its messy pulling that plug, so be prepared and its wise to hoses off the area that gets coolant sprayed on cause it may be acidic. After draining it thoroughly technically you can put whatever coolant you want 50/50.
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