This is a coolant expansion tank for your Mini Cooper R52 or R53 02'-06 , Supercharged Mini Cooper'. Made by Hella Germany. The tank is made of plastic and comes with a replacement cap. BMW part number is 17 13 7 529 273.
Fitment:Make Body Model Years
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MINI R52 Cooper S Conv 02-07
MINI R53 Cooper S 02-06