- Search for the "partial cooling overhaul DIY" I wrote a while back when my 2006 X5 M54 was at 115K: Wahler tstat, reservoir, tstat, cap, belts, pulleys, fan clutch etc.
- If you have more than > 150K, then do a entire cooling overhaul.
- The reservoir, use BMW only. Interestingly, I bought this from a BMW dealer, who is trying the get rid of old stock for cheap. Normally, the reservoir is $100 or so, this (Century Auto BMW dealer) is selling it for $55:
https://www.ebay.com/itm/Genuine-BMW...1/122630659270