Temperature gauge

Heating, Cooling & AC

  1. 1965ply

    1965ply Active Member

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    I have 1965 belvedere with a 383 car does not run hot but mech temp gauge does not move when car is first started and warmed up. I can be driving car and temp gauge will all of sudden pop up to 180 Degrees.could be 20 Minutes or 1 hr.. car has a cross flow aluminum rad, aluminum water pump and housing mopar performance..mech gauge was a brand new stewart Warner, I did change it thinking gauge was no good. Bought new gauge from summit does the same thing. The other day after car was hot and running, gauge was at 0 I did crack open the temp gauge on the housing and gauge popped up 165 it's almost like there's air pocket but it's been doing this for two years.. once gauge comes up it's ok until car sits overnight or a long time to cool off
     
  2. FrnkNsteen

    FrnkNsteen FBBO Gold Member FBBO Gold Member

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    My guess is that the sender is bad, or not getting good ground in the water pump housing. Here's what I would check,... Take an ohm meter and put red lead on the sender connection, and black on on ground. Check the ohms when cold and watch ohms reading while it warms up. Ohms should start at around 75-80 ohms when cold and smoothly drop as the car warms up. Ohms reading should be somewhere around 23-25 ohms when at normal operating temperature (Approx 180 degrees). If it lags (holds at 70-75 ohms, then suddenly drops to 25,... you have something going on with the sender and your gauge is probably fine.

    Quick question though,... how quickly does it "Pop" up? These gauges typically react pretty slow as the bimetal strip in the gauge needs to warm up from current flowing through it. If it is jumping quickly, I'd check to make sure the needle isn't rubbing somewhere, but I can't see it being very likely for two different gauges to do the same thing like that though.
     
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    • 1965ply

      1965ply Active Member

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      Thanks, but it's the mechanical gauge not the electric one that's what is puzzling gauge on dash doesn't work
       
    • FrnkNsteen

      FrnkNsteen FBBO Gold Member FBBO Gold Member

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      Oh, ok. Sorry,... Don't have much experience with mechanical temp gauges.
       
    • USatC

      USatC Well-Known Member

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      It sounds like the thermostat is opening and its responding to the sudden temp jump.
       
    • ksurfer2

      ksurfer2 Well-Known Member

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      I have an aftermarket temp gauge in my 69 RR and it does exactly the same thing.
       
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      • Ranger16

        Ranger16 Well-Known Member

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        That's odd. I too have an aftermarket mechanical temp gauge on my '69 Road Runner and it does nothing of the kind. Operates just as you would expect it to.

        I does indeed sound like an air pocket, but that should alleviate itself once it makes its way to the radiator.
         
      • David Buettner

        David Buettner FBBO Gold Member FBBO Gold Member

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        Where on my max wedge can I install a mechanical water temp sensor. I don’t want to lose the OEM sender.

        It is too small anyway.
         
      • khryslerkid

        khryslerkid FBBO Gold Member FBBO Gold Member

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        If you're not useing your heater you can use one of the water pump housing ports with an adapter. I believe I found my adapter on Summit.

        20190914_230951-jpg.jpg
         
      • RJRENTON

        RJRENTON FBBO Gold Member FBBO Gold Member

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        Gentlemen,
        I experience the same issue. I'm using a 2 5/8" diameter case Autometer instrument which is a mechanical gauge. It is a vapor pressure type instrument that is actually a low pressure gauge calibrated to read temperature in degrees F (or degrees C). The sensing element is immersed in the coolant near the thermostat housing and when heated, the vapor expands and the increase in pressure is tranfered to the gauge via the flexible capillary tube, which reads a higher pressure (temperature) on the dial. What causes it to "stick" or slow to respond innitially MAY be related to the capillary tube routing or if its restricted somewhere in its routing. To me it's a small nuisance as the dash temp gauge still functions. I have more faith in the "mechanical" instrument, even though it occasionally sticks, than in the dash instrument whose accuracy is marginal at best. Just my opinion of course.
        Bob Renton
         
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        • khryslerkid

          khryslerkid FBBO Gold Member FBBO Gold Member

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          You can see where mine is mounted. It's high up in the housing so the chance of a air bubble will be more likely. Once in a great while my guage doesn't read anything but I know I'm ok by the factory electric guage in the dash. Five minutes down the road she'll start working again and it's ok the rest of the day.

          Any mechanical temperature sending unit that I've had experience with has to have contact with the coolant. Air or steam won't cut it.
           
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          • RJRENTON

            RJRENTON FBBO Gold Member FBBO Gold Member

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            KK,
            As noted in my explanation, the "mechanical" temperature gauge's sensing element is the part immersed in the coolant stream. There is a vapor sealed in the sensing element and capillary tube at the time of manufacture. It is the vapor expansion that relates to the coolant temperature. The instrument measures PRESSURE of the expanding transmitted vapor to the temperature calibrated dial. It has nothing to do with any air bubble....once the coolant system is circulating, any air in the system will collect at the top of the radiator.
            Bob Renton
             
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            • khryslerkid

              khryslerkid FBBO Gold Member FBBO Gold Member

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              You are correct. What I stated is the "bulb" has to have coolant contact. Air or steam isn't enough to activate it. I think we both are stating the same thing.
               
            • David Buettner

              David Buettner FBBO Gold Member FBBO Gold Member

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              I understand I can use the heater port, but I don’t want to lose the heater function. Any suggestions?
               
            • khryslerkid

              khryslerkid FBBO Gold Member FBBO Gold Member

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              Do you have a pipe plug in this location that you can remove? Some housings don't.

              P6160010-1.jpg
              GTX underhood (12).jpg

              (Swiped the pics from a couple of threads on here about this topic)
               
            • 66chargerpat

              66chargerpat Well-Known Member

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              If you have the sending unit in the 3/8npt port next to the alternator bracket, it will only read the temp of the water coming from the rad. this water will stay cool till the stat opens.
               
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