The coolant expansion tank provides an buffer for the coolant to 'overflow' to when the cooling system is running. Replace yours with a new one if there is lots of corrosion inside, or if it happens to leak.
17-11-7-573-781-M58
Coolant Expansion Tank (cap not included), BMW E46 3 Series, All Except M3 (1999-05), Each Brand: OEM [More Info]
$76.75
17-11-2-283-344-M9
Coolant Expansion Tank (cap not included), M3 (2001-06), Each Brand: Genuine BMW [More Info]
$129.00
Water Drain Plug
17-11-1-707-818-M9
Water Drain Plug, in Expansion Tank Mounting Plate, E46 323i/Ci Cpe/Ci Conv, 323i Wagon, 328i/Ci, 330i/Xi/Ci Cpe/Ci Conv, 325i/Xi/Ci Cpe/Ci Conv, 325i/Xi Wagon, Each Brand: Genuine BMW [More Info]
