Very close to losing my AWD v50 to this.
That crazy looking radiator hose that has the 2 plastic junction bits in it was leaking slowly, I only noticed because I went to top up the low washer fluid, which has a warning by the way, but not the coolant level.
Expansion tank was totally empty, temp gauge normal.
All cars should have low Level warning for this, my newer Volvo don't even have a temp gauge visable, what's that nonsense?