what I don't understand is why the car will idle forever at about 92/93c and not overheat. I thought car engines were more prone to overheating when standing still as no air flow and fan not on?? When I drive and temp goes to 124C and I stop with engine still running temp comes down by about 20c in as many seconds, surely that is impossible, even with fan on. Please advise? That is why I thought sensor was giving false reading.

Tried infra red thermostat but having read instructions it only reads surface temperature and not core temp, so cannot give an accurate reading. Temperature right at the back of the engine on the metal part (behind cylinder head) does read high (106C) when engine idling, but I expect that is where the combustion takes place?,

Having said that bottom rad hose is still cold and only warm when engine idling.