Mechanical Temperature gauge fluctuations

Heating, Cooling & AC

  1. RJS

    RJS Well-Known Member

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    I bought my car with temp. gauge fluctuations, so first thing I did was replace gauge with a new Auto meter gauge ATM-3432. Still happened from time to time. I have a 180 Mr. Gasket thermostat and a Moper Performance aluminum housing and WP.
    I don't have a temperature gun yet but plan to get one. I also have the factory dash gauge hooked up but he sits at the first line after warmup and is consistent.

    I now found I had room for another 1/2 gallon of 50/50 mix Prestone/water thinking that would help but no still happens. I changed to a 160 Mr.Gasket stat. and it seems to move the gauge pretty regularly from 170-210 sweep.
    The car doesn't boil-over and under the hood isn't hot like when you have a hot running car. Also has a 16lb. restoration type cap and this was with two different aluminum radiators also.
    Has anyone else ever had weird gauge movement with a similar set-up? I feel that I'm dealing with a steam pocket/air pocket in that corner of the housing.
    If I just had the factory gauge I would never know this was happening.
    My next plan is to put the two heater hose fittings in the housing and just loop a 5/8" hose to see if my air pocket would possibly move or am I wasting my time

    Thanks Ron

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    Last edited: Oct 25, 2021
  2. Cranky

    Cranky Henchman #1 Staff Member FBBO Gold Member

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    My diesel fluctuates like crazy and after replacing the stat several times, it got better but still would heat up to normal op temp then falls to around 140 then start going back to 180. In the winter time it wouldn't even warm up to op temp. Got tired of messing with it and just put in a radiator block/cover in winter. Been wanting to make a new one for summer time so my AC will continue to cool at stop lights. In 70 degree weather, I can put in a solid cover which covers 90% of the radiator and it runs at 180 and won't climb at stop lights unless it's a really long light. The dang radiator is almost 37" wide....97 2500 Dodge. Don't know if you would be wasting your time or not but worth trying.
     
  3. F4R/T

    F4R/T Well-Known Member

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    Be careful with those Mr Gasket stats! I’ve had two high flow fail in a row on my buddies charger and it caused an accident when the hose blew off because it stuck shut.. Those are unreliable. They are China made , I switched personally to the high flow Milodon and no issues yet..
     
  4. RemCharger

    RemCharger Well-Known Member

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    Picture of your temp probe in the motor might help
     
  5. RJS

    RJS Well-Known Member

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    I provided a picture which shows the cable and probe on water pump housing passenger side and factory sender and wire on driver side.
    Ron
     
  6. RemCharger

    RemCharger Well-Known Member

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    I see a picture of a very nice engine bay but how about a close up of the temp probe.
    As in; it looks like the probe might not be in the coolant passage properly.
     
  7. Mike67

    Mike67 FBBO Gold Member FBBO Gold Member

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    Are you sure with that fitting the probe is not in an air pocket?
    I bought one of those vacuum fiitings that allows me to put the block under vacuum and then force fills it to ensure there are no air pockets.
     
    Last edited: Oct 25, 2021
  8. steve340

    steve340 Well-Known Member

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    You could be right about air pockets. The heater core if connected properly was designed to bleed any air out of the cooling system.
     
  9. RJS

    RJS Well-Known Member

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    Close-up of the red bushing Auto Meter provides with the gauge and the probe. This is how Previous owner installed and i just followed suit when I replaced the gauge.
    Is this not how it's supposed to be???? Explain.
    Ron

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  10. RJS

    RJS Well-Known Member

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    That's my best guess right now so when the heater core nipples arrive I'll loop them till my Vintage Air system arrives.
    Ron
     
  11. steve340

    steve340 Well-Known Member

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    I had a problem with similar issues with a 302 Ford Windsor in a hot rod truck - erratic temperature fluctuations on the gauge but no engine overheating , boiling or loss of fluid.
    Did all the usual things - still the same.
    Looped the highest up heater connection back to the water pump and instant positive result.
    I hope you are as lucky.
     
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    • gtx6970

      gtx6970 Well-Known Member

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      Best thing I did to mine for temps was going with a Stewart Components tstat.

      its a 160 ( planning to up to a 180 here soon )

      And my cars temp gauges stays rock solid at 180-185 range , even on days where the ambient temps are well over 100
       
    • RJS

      RJS Well-Known Member

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      Bill I really feel this isn't a "temperature" issue but just a fluctuating gauge issue. As soon as I get the 5/8" nipples I'll test and see if this goes away. The factory gauge isn't indicating any trouble at all but it's screwed into the left top of housing. Was just hoping to hear maybe one or two people have had similar issue and I have to say that Steve340's comment is giving me some hope for now.
      Ron
       
    • steve340

      steve340 Well-Known Member

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      If it is air bubbles this can cause erratic operation of the thermostat as well.
      You are trying what is simple first and that is a good plan.
       
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      • RemCharger

        RemCharger Well-Known Member

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        My concern was that the temp probe wasn't far enough in the coolant port, and maybe hiding an air bubble in it.
        You could try loosening the the probe until coolant leaks out and then tightening up.
         
      • RJS

        RJS Well-Known Member

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        The other day when I swapped the stat. I took a real good look at the probe to make sure it was in all the way or not too much and bottoming but all seems correct. The red bushing will only go so far into the housing and then the probe goes into it and seats nicely.

        Your idea about backing the probe out a little (basically burping the system) is a good one incase air pocket is there in the corner of housing. I'm working on the rearend right now so once that's done I'll have the nipples to test
        my loop theory.
        Ron
         
      • khryslerkid

        khryslerkid FBBO Gold Member FBBO Gold Member

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        Pretty much where mine's located, no problems. Stock iron housing. Once in a great while the guage won't move from dead cold when the engine is up to temp. As soon as I start down the road it's where it should be. I don't have any heater hoses hooked up.
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