What year is your FC? On the 86-88's there is a bleeder screw on the radiator next to the inlet neck that connects with the outlet on the water pump. On the 89+'s they relocated the filler neck to try to prevent this from happening, but it still does every time I refill my coolant after flushing. Did you just flush yours? I hope so, as you shouldn't be getting air in there without draining the coolant.