Check car thermostat: How could I know whether a thermostat got stuck closed or stuck open?

Someone said: To check, you should touch upper hose and lower hose. If one is hot and one is cold, it means thermostat stuck closed. But which is hot, which is cold: Upper? lower? Or it doesn't matter? And, when is the thermostat stuck open? Thanks a lotCheck car thermostat: How could I know whether a thermostat got stuck closed or stuck open?Stuck open takes forever to get heat. Stuck closed overheats and light or Gage reads hot. As cheap as thermostats are if your in question replace it and then your sure it is good.Check car thermostat: How could I know whether a thermostat got stuck closed or stuck open?It seems to me that if it's stuck closed your engine will overheat. If it's stuck open your heater may not get warm in really cold weather.



So you could run your engine a little while and keep an eye on the temperature gauge. If it begins overheating shut it off and change the thermostat.Check car thermostat: How could I know whether a thermostat got stuck closed or stuck open?no thats false if it is stuck closed it is going to overheat if it is stuck open your you will be wasting fuel for a while nd it will take a while to heat upCheck car thermostat: How could I know whether a thermostat got stuck closed or stuck open?if it is stuck closed you will know as soon as your car starts to warm up as it will overheat right away.Check car thermostat: How could I know whether a thermostat got stuck closed or stuck open?If it's stuck closed the return side will be cold (top hose in most radiators).



If you take out the thermostat, you can put it in a pan and boil it. It should open when the water starts to boil and then close when the water cools.