Thanks for the update! My goal is to build my own controller and maybe focus on running the existing aux fan with a strategy similar to what the X3 uses. I might add a second fan for redundancy. No time though, so just running without mechanical fan in the winter for now.

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1988 325is (purchased new) sold
2004 X5 3.0 2005 X3 2.5
2008 X5 3.0 (new to me)