Originally Posted by duncan_156
This post has received a number of cynical replies - I don't know why. I, for one am keeping an open mind and at the moment I'm inclined to give the Alfa-trained mechanics the benefit of the doubt unless somebody equally qualified can tell me different and explain the basis for the differing view.
The thermostat should not open until somewhere between 81-85degC, so if yours has a normal running temperature of below 81degC the thermostat is faulty.
The temperature sensor is also located on the thermostat housing at the hottest point of its cooling cycle, so it sees the same temperature as the thermostat.
Just believe the people who have already replaced their own thermostats (including me!)...:
Running temperature when new: 90degC
Running temperature after a couple of years: 70degC
Running temperature after replacing faulty thermostat: 90degC
ALL modern engines are designed to run as hot as possible (with a safety margin as Sunbar said), usually this ends up between 85-95degC.
Remember too that 100degC isn't boiling either, one because the system is under pressure, raising the boiling point, but also because the engine coolant isn't water... the coolant I use doesn't boil until 180degC.!!