Just started coolant flushing (it was green not pink) and the thermostat is OK, plus difficult to remove, under the fuel pump. I was following Hatboy Harveys tutorial but avoiding the thermostat replacement. It suddenly dawned on me that you could have air trapped behind the thermostat but then again  it might not, otherwise you wouldn't be able to put the new one in with an empty coolant circuit.

It's OK i it's self bleeding.