Just to be clear, when I was saying they tend to fail open, I was meaning the FIRE engined cars. I've come across other models/brands with thermostats failed closed but never on one of the wee FIAT motors.Apart from mine that was new and stuck shut, that was expensive on the Mazda
Your experience brings up an interesting point where car repairs are concerned and that is that we all tend to take it for granted that a new part is going to be perfect and operate exactly as it should. In most cases this is true but I've been spectacularly caught out a few times by new parts which were not at all up to spec. I always check now that a new part is satisfactory and compare it with the part it's replacing.