You can’t trust thermostat ratings

Heating / Cooling / AC

  1. hotrod swinger

    hotrod swinger Well-Known Member

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    I bought a 185 thermostat, it was stamped 185, yet my engine consistently runs at 170, no matter the season. Verified with a laser thermometer.

    Is it worth the time and energy to swap it out?
     
  2. toolmanmike

    toolmanmike Moderator Staff Member FABO Gold Member

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    I always test mine in a pan of water on the stove.
     
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    • hotrod swinger

      hotrod swinger Well-Known Member

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      Lesson learned.
       
    • Dana67Dart

      Dana67Dart The parts you don't add don't cause you no trouble FABO Gold Member

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      Where are you measuring?

      Thermal temp guns don't work accuritely on reflective surfaces.
       
    • hotrod swinger

      hotrod swinger Well-Known Member

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      I’m measuring a painted intake manifold directly below the thermostat housing.
       
    • RustyRatRod

      RustyRatRod I was born on a Monday. Not last Monday. FABO Gold Member

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      The thermostat hasn't a thing to do with how hot your engine runs. Nothing. The temperature stamped on the thermostat is simply when it begins to open.
       
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      • 66fyssh

        66fyssh Don't Stop Believin' FABO Gold Member

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        I don't think I'd worry about 170*. But if it's going to be one of things that you think about every time you drive, make time to swap it out. I learned to bite the bullet on those nagging little things that take up my valuable gray matter, lol.

        I wonder if the laser thermometer could be off also? Could be a combination of the thermostat opening a little early and the thermometer reading low.
         
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        • toolmanmike

          toolmanmike Moderator Staff Member FABO Gold Member

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          The lazer's are quite accurate. They measure surface temperature and not coolant temp.
           
          Last edited: Nov 19, 2021
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          • RustyRatRod

            RustyRatRod I was born on a Monday. Not last Monday. FABO Gold Member

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            Correct. This is why any nurse will tell you to add "about" 3-5 degrees to an infra red gun if you use it to take a person's temperature. The temperature of your forehead's surface isn't quite representative of your overall body temp.
             
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            • hotrod swinger

              hotrod swinger Well-Known Member

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              I get that it has nothing to do with maximum temperature, but I had understood the thermostat dictates the minimum temperature, which is what I’m concerned about.
               
            • hotrod swinger

              hotrod swinger Well-Known Member

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              Then again, if 170 is a good operating temperature I’m happy anyway.
               
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              • MOPAROFFICIAL

                MOPAROFFICIAL FABO Gold Member FABO Gold Member

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                The thermostat rating is the temperature of which it is fully opened. The thermostat starts opening a lot sooner but it's not fully open until the rated temperature. Fact.
                You can take a 180 thermostat n put it in a pot of water on a lit stove..and with a thermometer in it you'll see it starts opening about 150 degrees.
                We learned that in HS auto shop class.
                 
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                • MOPAROFFICIAL

                  MOPAROFFICIAL FABO Gold Member FABO Gold Member

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                  You can use less fan, or a higher rating stat...but... idk. It's your car. Idt it would hurt it. There is an expansion rate at a given temp for cast iron and I guess you would want to maintain a range in regards to the clearances vs temp spikes @wot ...its really overthinking it though. Lol
                   
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                  • dukeboy_318

                    dukeboy_318 FABO Gold Member FABO Gold Member

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                    Ratings on anything anymore it seems have a wider tolerance band than it used too
                     
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                    • AJ/FormS

                      AJ/FormS 68 B'cuda fb, Form S clone ... 367/A833/3.55s FABO Gold Member

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                      on a streeter, I would.
                      Yours is probably not closing all the way.
                      They say your street engine will last longer if run a lil warmer. I get great power out of mine at 205, and better fuel-economy on the hiway.
                       
                    • MOPAROFFICIAL

                      MOPAROFFICIAL FABO Gold Member FABO Gold Member

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                      They've always worked this way.
                      It's hearsay on how they work that's confused people over the years.
                       
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                      • hotrod swinger

                        hotrod swinger Well-Known Member

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                        Of course I ended up changing the thermostat. What else would I do on a rainy day?

                        I bought a 195, the one that was installed was a 180.

                        Tested both last night, both close properly, the 180 opens at 160 and the 195 opens at 185. I installed the 195.
                         
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                        • harrisonm

                          harrisonm Well-Known Member

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                          Gotta disagree with that. Everything I have ever seen or read stated that the temp on a thermostat was when it started opening. @RustyRatRod was an Oriellys manager for years, and I agree with him.
                           
                        • hotrod swinger

                          hotrod swinger Well-Known Member

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                          These were the temps they started to open.
                           
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                          • MOPAROFFICIAL

                            MOPAROFFICIAL FABO Gold Member FABO Gold Member

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                            If that makes your butthole moist, sure.
                            No knock on Rob.
                            You're still wrong.
                             
                          • MOPAROFFICIAL

                            MOPAROFFICIAL FABO Gold Member FABO Gold Member

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                            Thank you for actually doing the footwork most people either just believe or deny it and never tested themselves.

                            They start opening before the temp rating at which they are fully open at.

                            People think they just POP open..lol.. yeah.. a big pressure spike is what you want...not.
                             
                          • MOPAROFFICIAL

                            MOPAROFFICIAL FABO Gold Member FABO Gold Member

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                            As they cycle the 195 will start opening a little sooner..like maybe 3-5 degrees sooner.
                             
                          • hotrod swinger

                            hotrod swinger Well-Known Member

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                            Also my engine now runs at 180-200 instead of 160-180, so the thermostat definitely has an effect on operating temperature.
                             
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                            • MOPAROFFICIAL

                              MOPAROFFICIAL FABO Gold Member FABO Gold Member

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                              The post above yours proves you wrong too.
                              Lol did you miss that?
                               
                              Last edited: Nov 28, 2021
                            • Tooljunkie

                              Tooljunkie King of cobble/master of the broken bolt FABO Gold Member

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                              2 types of thermostats. Graduated and reverse poppet. Graduated are fully opened at 180, and poppet style start to open at 180. Quick open quick close. Poppet style typically cycle open and closed.
                               
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