Coolant pukes out of overflow tube after shut off

Heating, Cooling & AC

  1. Davison

    Davison Member

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    1972 Road Runner 440: Had been running perfectly in 75-90 degree temperatures. No issues. Oil pressure right in the middle of the gauge, water temperature in the middle to slightly to the left, cool side. No problems of temperature gauge going to the hot side at stop signs or traffic lights. However after pulling into the garage and shutting it off, about 20 to 30 seconds later the coolant pukes out of the overflow tube on to the garage floor. About a half a cup of coolant and then it stops. Going back into the car and turning on the ignition shows that the water temperature gauge is pegged in the red zone all the way to the right. The car had a major service in 2018, new coolant, new radiator cap, new thermostat, radiator taken out and cleaned. All hoses are 5 years or less. This problem just showed up the last three times I took the car out, otherwise for two years, no issues. Any ideas as to where to start to fix it?
     
  2. Tony Tee

    Tony Tee Well-Known Member

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    Overflow reservoir? Downflow radiator with the tank on top and bottom? The top tank should not be filled all the way to the top. Needs room to expand? I'm just thinking.??
     
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    • rumblefish360

      rumblefish360 Well-Known Member

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      Time for a new radiator cap I think. It sounds like the spring and seal aren’t up to par anymore.
       
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      • Davison

        Davison Member

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        No overflow reservoir on this car, Yes, i thought it might be too full. I checked the Service Manual: should be 1" below bottom of neck to tank. it's below that now.
         
      • Davison

        Davison Member

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        That is a simple fix. So I hope that is it. I'll try NAPA today.
         
      • Ghostrider 67

        Ghostrider 67 FBBO Gold Member FBBO Gold Member

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        Cap.
         
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        • Longknife

          Longknife Member

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          Either the cap or its too full. I know the manual says 1 inch below neck but as long as the level is covering the core when cold you will be ok. Test cap or replace, thats less than 10 bucks, if it still does it let it puke a couple of times and watch gauge and level,,,PS Its ok for the temp gauge to peg after shutting off, the engine is still HOT and the coolant stops circulating so it will peg, expanding the coolant...
           
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          • toolmanmike

            toolmanmike Moderator Staff Member FBBO Gold Member

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            Yep, cap or too full. Cap not holding pressure. When you shut it off the coolant superheats and boils because it's not under pressure.
             
            Last edited: Jun 30, 2020
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            • Mike67

              Mike67 Well-Known Member

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              I would agree about the cap, or another possibility is that you have air trapped in the block.
               
              Last edited: Jun 30, 2020
            • toolmanmike

              toolmanmike Moderator Staff Member FBBO Gold Member

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              He has been driving it for years and it just started happening. I don't think the system has been opened.
               
            • Davison

              Davison Member

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              Thanks to everyone. It was the cap. I went to NAPA and they charged me only $6 for a new cap. I looked closely at the cap that I had on the car. It had a Chrysler part number on it, so I assume it is original to the car or a 1970's era replacement. Anyway, perfect low cost solution and quick too.
               
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              • MOPAR MARTY

                MOPAR MARTY Member

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                I HAVE HAD NO LUCK WITH THE PARTS STORE CAPS . MY ADVICE TO U WILL BE TO WATCH THE CAP i bet u will be changing it again sooner than later the other thing thay like to do is over pressure blowing the system up. i have seen it many times that's they made a cap pressure tester
                 
              • toolmanmike

                toolmanmike Moderator Staff Member FBBO Gold Member

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                Good you got it fixed for a few bucks. Cruise on!
                 
              • Mike meeks

                Mike meeks Member

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              • Mike meeks

                Mike meeks Member

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                You probably don't want to hear this but I had the same problem and suffered through it for a summer until it got progressively worse to the point I could not drive the car I thought it was a head gasket I pulled the head off replace the gasket it was not the problem what was the problem was that cylinders 2 and 4 head large cracks in the cylinder wall about an inch down from the deck 2 in long people that know these motors very well see this eventually happens that those two cylinders are inherently weak might want to do a pressure check . I played around with the cap and all that stuff in that was not the problem like I say the problem got progressively worse and I would take the car out for 20 minutes and it would puke everything out
                 
              • toolmanmike

                toolmanmike Moderator Staff Member FBBO Gold Member

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                He fixed it with a new cap. A problem like he experienced could be a long list of things with a bad head gasket on the list.
                 
              • Mike meeks

                Mike meeks Member

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                I'm happy that's all it was, my block was a '65 383 with a lot of hard use
                 
              • Davison

                Davison Member

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                Thanks for the heads up. i will keep an eye on it. So far, so good.
                 
              • rumblefish360

                rumblefish360 Well-Known Member

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                • toolmanmike

                  toolmanmike Moderator Staff Member FBBO Gold Member

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                  Fat fingers on a cell phone? LOL
                   
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