My friend had the car - all was working fine - the thermostat was working fine (it was a relatively new one that had been put in as the previous one was stuck in the open position - and had done about 3,000 miles since thermostat replaced with no problem) - he was stuck in traffic for a while and it was getting warm. He kept switching the car off to avoid overheat. Car was parked for three days, then he drove it again and there was a bang and a hole blown in side of radiator. Radiator was changed - still high pressure building in system after about 15 miles. Thermostat was removed - still high pressure in system after 15 miles. So, there is no thermostat in the car - and all was fine until the radiator blew. Seems to be pressure building up in the system somewhere - but just can't work it out!!!