For M52 and M54 engines:

- Tstat ---> Wahler is the OEM
- WP: I use HEPU brand, put it in my 1998 528i at 90K, and I am now at 150K, zero issues.
- Radiator: Same for Nissens, out it in at 90K, zero leaks.

V8 is another pandora box.

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1998 E39 528i 5sp MT
2006 E53 X5 3.0 6sp MT