radiator is an airtec ally one.not sure on age as was fitted before I owned the car.does seem poss rad related as by using heater to cool heater matrix its doing the radiators job with the airflow.
water pump is working as I rev it I see coolant going back into the header tank.my turbo was water cooled but used to boil the water like a kettle on boost so have disconnected that which did help but now summers coming its warming it up again
would a swirl pot make a difference as mine doesn't have one?

tbh I'm not sure its a fan problem as driving at motorway speeds the natural airflow should cool the rad and fans not be used.