Did you get the tank all the way on?

I used aftermarket part and it took my entire body weight to get the thing to seat. If all you need to do is re-seat you can pull it up a bit and have a new go at it. You will just spill a couple oz. of coolant.

You could use a ratchet strap to help pull it down. Do you recall if the retention spring clicked?

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2011 E70 • N55 (me)
2012 E70 • N63 (wife)