2006 Fiesta Duratec spewing coolant

[Matthius]

Hi
First post
New to site and sorry if this has been covered already.
I had a thermostat housing with new thermostat replaced 2 years ago.
Its has done 2000 km since then with no problems as the car is not a daily drive.
So recently the car after 10 minutes of running then suddenly unloads a lot of coolant with the temp gauge reading normal with no external leaks other then the tank.
I have pressure tested the system that passed and have used a bottle on the expansion tank to help bleed.
I can hear a sorta vacum leak under the alternator.
Is it possible that the pump or thermo housing is suckin air ?
Big thank you for any response