But what indication do you get if the thermostat fails open? My car was picked up by trailer to return to dealer, I was told on no account the car should be driven.
If it gets too hot it’ll put up an error message.
The problem with a thermostat which fails fully open (and they are designed to be more likely to fail open than closed) is that it looks ok when stuck in traffic but on the motorway the temperature goes down below normal and you won’t see that without a water temp gauge.