By this time, you need to do at least a partial cooling
overhaul.

Most important are WP (I use HEPU brand) and Thermostat (I use Wahler).

If you have a healthy cooling system, the fan clutch's role is less important.

Info on cooling overhaul is in forum, I wrote it around 2015 or so.

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