E90 320d water and fan

Hi guys,

I need some help, how do I test my radiator fan, I have never seen it spin, yesterday I got a water level warning, lucky it was in my driveway, opened the water bottle and I had to fill abt a liter of water, I looked everywhere and def no leak, since then it never drop in water level as yet, but I was wondering i never seen the fan spin, I left the car to idle abt 15 mins thinking that the fan will spin but it never,

I'm sure it must be working cause I never ever got a temp warning, but was just wondering how do I test it.

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Sorry just to add, since I got the car over a year ago, it never a single drop of water, besides, yesterday,

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And is there a way to get the fan to kick in earlier, or should I just leave it,