1/could be water pump impellor loose.
2/air lock.release bleed screw on rad and run at 2000 until thermostat opens ,watch the water level.
3/viscious fan faulty.to test with engine running,use rolled up newspaper and see if you can stop the fan when cold,if you can warm up to normal temp (or hot)and see if you can stop the fan again,if you can the coupling is faulty.any probs let me know.