Can't help with why the expansion tank cracked (although I understand that is a very common issues on petrol X5 cars related to age and heat) but I CAN tell you the aux. fan operation looks totally normal. The twitching at start up is part of the fan start diagnostics and they all do it.

*edit* and yes, activating the fan via INPA or ISTA/D will cause it to go through the start up cycle, then run up to full speed. There doesn't seems to be a way (or a need) to test it at lower speeds.

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Wayne
2005 BMW X5 3.0d (b 02/05)
2001 BMW F650GS Dakar (b 06/01)