Interesting Problem with Overheating

Heating, Cooling & AC

  1. JimKueneman

    JimKueneman FBBO Gold Member FBBO Gold Member

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    For those that followed me restore my '68 318 Coronet they know that I went through _everything_. The 318 was rebuilt very mildly to factory tolerances. New GlenRay reproduction radiator, GlenRay recored heater core (factory A/C car), new... well everything else, hoses, water pump, H valve, restored temperature control valve and the list goes on.

    I have noticed something weird in the 6 weeks that I have driven it and yesterday I was really able to do some experiments since it was hot in Tucson and I was alone so I did not get the family complaining in my ear.

    The first thing I noticed was in the mornings it seems to be hit and miss if the heater would blow hot air. I could drive 40 miles to work get off the freeway and the heater would blow luke warm. I would hit the off ramp and all of a sudden my feet would be on fire as it started to blow hot. This happened several times. A few weeks ago it was about 100 in Tucson and I drove it in traffic and I could not keep the AC on. Even with it off it was hard keeping it under 205F and it would creep to 208 at the lights at times. We got a cool snap and in the interim installed a new fan clutch as the original would spin numerous times after I shut the engine off when hot. The new one comes to a quick halt when I shut it off hot.

    Yesterday was interesting. Driving down a 2 lane country road at 65 it leveled out at around 199F, bit more up hill, bit less downhill. Hit the freeway and it crept up to around 203 (note the AC was on all this time). Got into Tucson and as I went from light to light it crept up to 206. I turned off the AC and it went down a bit but it was clear it was heat soaking and slowly crept higher. At about 208 I flipped the heater on and it dropped to about 200. I then realized that the air ALWAYS flows through the heater core so I fired up the AC with the temperature on HOT. With the cooled air blowing through the heater core it dropped immediately to 197F. Of course only the car was happy, I had 200F air blowing on me in 100F traffic......

    Then I went to a car show and left around 9pm. The windows were down and the temp dropped into the low 60's upper 50's so I wanted to run the heater. Guess what, it would not blow hot air... It did not blow hot the entire way home. This is getting a bit perplexing. Anyone have any thoughts?

    Jim
     
  2. Billccm

    Billccm FBBO Gold Member FBBO Gold Member

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    Hi Jim
    I assume you are confident there is no air bubble in the cooling system. You don't have any coolant loss, correct?
    Hopefully you don't have something floating around as an intermittent blockage?
     
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    • JimKueneman

      JimKueneman FBBO Gold Member FBBO Gold Member

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      No loss of coolant. Won't quite stay full as it heat soaks and spits the top inch of the radiator on the ground.
       
    • Billccm

      Billccm FBBO Gold Member FBBO Gold Member

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      Exhaust smells okay?

      I had an old crown vic police car with similar symptoms. It was the water pump. Electrolysis that had half dissolved a impeller. Probably not a water pump in your case. I'm still thinking.
       
    • turbo36

      turbo36 Well-Known Member

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      I had a similar issue with my 65' Belvedere, turns out the brand new thermostat I put in was not functioning properly. I diagnosed by putting the thermostat in a pot of water and watching the action as the water heated up.
       
    • Dennis H

      Dennis H FBBO Gold Member FBBO Gold Member

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      I see you have a shroud. Should not be an issue when moving anyway. My cooling issues were solved with replacement of a failing thermal clutch fan. Difficult to diagnose. Also 180 Stant Superstat, green coolant, and conventional copper radiator. Does your hood have the rubber sealing strip?
       
    • JimKueneman

      JimKueneman FBBO Gold Member FBBO Gold Member

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      194 Stant thermostat, green coolant, GlenRay factory authorized reproduction (copper) and all new sealing strips.
       
      Last edited: May 14, 2017
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      • JimKueneman

        JimKueneman FBBO Gold Member FBBO Gold Member

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        I had caved in to say this is how these old cars are until I met a guy last night who bought a 100% original '69 Charger with a 383 and AC from a guy who bought it new in 1969. He said he can run around town all day long with the AC going and it never gets over 185....
         
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        • Billccm

          Billccm FBBO Gold Member FBBO Gold Member

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          Still thinking. Can you burp one of the heaterhoses? Any possibility of the impeller being loose or damaged?
           
        • Billccm

          Billccm FBBO Gold Member FBBO Gold Member

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          I can agree in that my 69 coronet with 440 and factory AC never got hot, but I've noticed many big block mopars out there nowadays with electric fans added as assist in front of the radiator.

          I hope this isn't one of those weird problemswith a incorrect head gasket or mis torqued head, etc.
           
        • Dennis H

          Dennis H FBBO Gold Member FBBO Gold Member

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          No need for pushers or pullers. Ma knew. Mine stays cool under extreme conditions. It does not like 5000 feet altitude as it is tuned for sea level. Would be perfect if non- ethanol was available. I'm in the burp camp. The more I drive and beat on mine the better. Boil out the contaminants.
           
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          • JimKueneman

            JimKueneman FBBO Gold Member FBBO Gold Member

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            So what is the best burp procedure?
             
          • Billccm

            Billccm FBBO Gold Member FBBO Gold Member

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            Simple procedure is pull the front onto ramps. Remove radiator cap. Sit overnight and see of coolant level drops.

            Complex procedure is remove highest heater hose at core and helper is filling radiator. While coolant is flowing out of heater hose you connect to core.
             
          • Dennis H

            Dennis H FBBO Gold Member FBBO Gold Member

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            Others here know better than me. I'd idle to op temp with the cap off, then drive it. Are you using a laser temp gun?
             
          • JimKueneman

            JimKueneman FBBO Gold Member FBBO Gold Member

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            FiTech fuel injection coolant temperature readout. I compare it to the gauge. At 200 the gauge is just a hair over half. At 210 it is right at the hot line. After a heat soak it is typically 213 or so and it is pegged hot.
             
            Last edited: May 15, 2017
          • coloradodave

            coloradodave FBBO Gold Member FBBO Gold Member

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            I'm with Dennis on the laser temp gun. My FiTech handheld read 30* cooler than my Autometer mechanical gauge which agreed with my temp gun. FiTech suggested buying an AC Delco #213-928 sensor ( $15.74 at Rock Auto), which they said was more accurate than the one they provide. Now it reads about 10* cooler.
             
          • Billccm

            Billccm FBBO Gold Member FBBO Gold Member

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            Jim I shared your original post with the mechanical engineers here at work that are also big (Chevy) motorheads. One suggestion was to drill a small hole in the thermostat to burp/vent the system at all times and allow (their term, not mine) a 'signal flow' of coolant to help stabilize wild hot and cold trends to the thermostat. The other recommendation was to try a few different radiator caps both in brand and pressure.

            When I mentioned that I had Crown Vic Police with a similar issue and it was a half dissolved water pump impeller, one of the guys asked if your water pump impeller was nylon, or metal. It was mentioned to me that nylon impellers can 'slip'.

            Hope this helps.
             
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            • Billccm

              Billccm FBBO Gold Member FBBO Gold Member

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              "A common problem with older vehicles and less advanced cooling systems is that the temperature control loop with the cooling system causes the thermostat to function in huge oscillations a fix for this that allows some “signal temp coolant” to flow is to drill a 1/8 hole on the thermostat. This lessens those fluctuations."
               
            • oldbee

              oldbee FBBO Gold Member FBBO Gold Member

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              I have heard of difficult heating problems being traced to a w/p impeller slipping on its shaft. Radiator guys told me that.Just a thought
               
            • JimKueneman

              JimKueneman FBBO Gold Member FBBO Gold Member

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              The water pump is a GMB that was recommend by Dave at the machine shop. It is all metal construction and Dave says it is one of the higher quality after market available (Japan not China). I talked to Bob at GlenRay and we are going with a 180 thermostat and he told me to drill 4 1/32" hole in a cross pattern in it then run it with the cap off and get it hot and rev her up. If it ever stays hot here in Arizona I will report back the results.
               
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