From my experience I can declare. Test for thermostat in pan using thermometer shows nothing. I tried this test several times on different thermostat. In the pan they show that all is OK. They opened by the right temperature and closed properly. But they did not work on the highway. You can believe me. I live in the place were temperature can be lower then -35 degree Celsius. And thermostat is really critical part of the cooling system. Only new one solved the problem always.