Check Car Thermostat How Could I Know Whether A Thermostat Got Stuck Closed Or Stuck Open

Posted in Cooling Perfomance
  • 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 lot
    When thermostat stuck closed, usually upper hose is cold, lower hose is hot. But my overheated car is the other way around: Its upper hose is hot and lower hose is cold. Why? Could you advise? Thanks

    There are 5 Answers for "Check Car Thermostat How Could I Know Whether A Thermostat Got Stuck Closed Or Stuck Open"

    1. boiledcrabs says:

      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.

    2. james r says:

      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.

    3. tin2mik says:

      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 up

    4. mister ss says:

      if it is stuck closed you will know as soon as your car starts to warm up as it will overheat right away.

    5. G T says:

      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.

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