If it's what I think it's a known problem with a plastic hose fitting. I think you can get a metal one.

If that was leaking like it seems it would you'd be leaving a trail of coolant behind and topping off daily (before the break).

Get that fixed and you really should vacuum fill the coolant. I think I paid $70 for a very nice kit.

There is a chance this caused your issue but just a chance.

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