Thermostat (3rd gen) answers !

Right in the repair manual, open between 80 and 84 C (176 to 183 F), lift by 10 to 14 mm at 95 C (203 F), should be fully closed below 77 C (171 F). More information than that might be harder to find.

They're nearly bulletproof. Expanding wax opens them, a big spring closes them. To get one to jam open, you'd need corrosion or grot stuck in it, neither of which should happen if the coolant is changed often enough to keep the corrosion inhibitors active. Only way to make one fail closed is to severely overheat the engine some other way until the wax blows out. Other than those failure modes, who ever needs to replace one?

 

Corrosion products of aluminum in a liquid can have that white crystally/flaky look too. Had it gone a long time without a coolant change?

 

Why would you want to change the thermostat, my experience with thermostats is they stick closed and engine gets hot very fast, if the temperature is maintaining around 190, then there is nothing wrong with the thermostat, mine is pushing 290 k

 

Even if a thermostat cost the price of a beer, your wasting your money when you could enjoy a cold beer instead