Guys, do I have a temperature problem?

Heating / Cooling / AC

  1. cruiser

    cruiser Well-Known Member

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    Gentlemen: I'm searching for a solution to a vexing temperature problem in my very stock 1974 Duster. My car has the 225 engine, stock renewed head, EGR system disconnected, all in very good condition. When I start out, the coolant temperature takes about five minutes to climb up to about 210 degrees, then regulates back down to 195. If I run the car for a long drive, the temp goes down and regulates to 170 - 180 and slowly goes back and forth in that range. Outside air temp is 45 degrees. The temp stays there for the rest of the drive. Sometimes, the temp will regulate to 195 and stay close to this. The coolant temp gauge is accurate, wiring is good. New water pump, radiator and heater hoses, belts, no air in the system, stock coolant reserve system with a correctly operating NOS radiator cap, and I'm running a 195 degree Stant Super-Stat. I thought that with my thermostat, the coolant temp should steadily climb to 195 and stay there the entire time, regardless of the outside air temperature. Why does it initially overshoot, then vary as I drive it? Everything is very stock and in excellent shape. The engine runs fine. Any ideas? If you think I need to replace the thermostat, who makes the best one? The Stant unit that I have in now doesn't seem very good. Slant Six Dan, please weigh in. Thanks - BOB
     
    Last edited: Nov 19, 2020
  2. zakimodo

    zakimodo Well-Known Member

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    When I was a heavy equipment mechanic, there some thermostats that seem to need a "warm-up" themselves before they start to regulate more around their specified opening temp. Usually, the overshoot was minimal (~5*)
    This said I think there is a point when this behavior is pointing to a sticking/ failing/ crap t stat. I just recently went through this with the thermostat in my pickup (6.7cummins). It was a 190* t stat and was wanting to stay closed until 210, new thermostat solved the issue.

    Curious to see what others have to say as well.
     
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    • RustyRatRod

      RustyRatRod Lemmie see your b00bs. FABO Gold Member

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      What have you done to verify your temperature gauge is accurate?
       
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      • cruiser

        cruiser Well-Known Member

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        I had it professionally rebuilt and calibrated by a very good gauge guy. He installed a solid state voltage limiter when he rebuilt the cluster. Temp sending unit in the cylinder head is good too - an original Chrysler unit. Wiring all good.
         
      • RustyRatRod

        RustyRatRod Lemmie see your b00bs. FABO Gold Member

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        That's NOT verified. Look up the word.

        Unless you've verified it with a temperature gun, you don't know whether the gauge is accurate. "NEW" or "PROFESSIONALLY REBUILT" still don't mean "GOOD" unless they've been verified.
         
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        • A56

          A56 MoParAffliction FABO Gold Member

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          temperature-measurement-dogs-dog-rectal-thermometer-69994385.jpg only one way to determine that
           
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          • RustyRatRod

            RustyRatRod Lemmie see your b00bs. FABO Gold Member

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            • Agree Agree x 3
            • Thanks! Thanks! x 1
            • kursplat

              kursplat FABO Gold Member FABO Gold Member

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              and to answer your question, 210' is fine. only you can decide if you trust your gauge
               
            • cruiser

              cruiser Well-Known Member

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              It's working fine now with a new (not a Stant) thermostat. Temp no longer overshoots on initial warmup. Stays at 195. I'm happy, and so is my motor.
               
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              • MOPAROFFICIAL

                MOPAROFFICIAL FABO Gold Member FABO Gold Member

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                The stat is tired or faulty.
                It shouldn't hit 215 warming up, the stat is sticking..then snapping open. Hence the heat spike then its fine.

                Could use a 180 stat as well.
                 
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