I need to refill the cooling system and need to know how many quarts it takes. My research shows up 4.2, 5.5 or 6.3 quarts capacity. Does anyone know what is correct for the Turbo engine?

 

I just checked the manual, and it doesn't say. However, you should have more than plenty if you buy a gallon from your local MINI/BMW dealer and mix 50/50 with distilled water.

This is an apples/oranges comparison, but last year our local mechanic flushed the cooling system on a G35, and a premixed 1 gallon jug was more than plenty for the job. The second unopened jug was returned for a refund.