Running hot after partial coolant change

Heating / Cooling / AC

  1. Righty Tighty

    Righty Tighty Well-Known Member

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    Okay, here's the story: I recently did some work on the engine that involved draining most of the coolant. Upon filling with fresh coolant, I began by adding what I thought was about half the total volume with antifreeze concentrate; I would then top off the other half with water. (I now realize why it's better to mix 50/50 prior to adding to the car)

    To my surprise, the radiator was full way before I expected, and before I was able to add any water. The overflow reservoir was empty, so I filled that with water in hopes to at least dilute the coolant somewhat.

    I didn't do any other work to the cooling system other than addressing a couple very minor leaks.

    Now when I take it out, it runs into the 220-230 range within 25 minutes. Could the more concentrated coolant mixture be the cause for running hot like this?

    The car in question is a 71 Scamp, 318/904 with headers. 26" copper core radiator with a fan clutch.
     
  2. Northern Grit

    Northern Grit Well-Known Member

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    Might have trapped an air pocket. Pop the cap after its cooled down and see if its low.
     
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    • Righty Tighty

      Righty Tighty Well-Known Member

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      I've let it heat cycle several times since then, monitoring the level along the way and it hasn't come down at all.
       
    • dano

      dano Evil Handy Man

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      Could any of the work you did affect the cooling system? Did the tune change? Have you looked to see if the lower hose is collapsing?
       
    • Joey4speed

      Joey4speed FABO Gold Member FABO Gold Member

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      Sounds like its air bound.
      Idle it with the cap on half way for a bit, it may burb a bit, and spew but should seek its own level.
      Then you can let it cool, ck level, install cap properly and start over.
      At least moving forward, you'll rule out air bound.
       
    • Righty Tighty

      Righty Tighty Well-Known Member

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      The only work I did was address a small fuel leak, small coolant leak, and replaced exhaust gaskets. I did remove the distributor to raise the engine, but verified the timing after everything was buttoned up. The lower hose looks fine, although it is a universal type with the wire on the inside. I suspect even if it were trying to collapse, the wire would prevent that some.

      I'll try idling it with the cap half way on and see where that gets me.
       
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      • RustyRatRod

        RustyRatRod Lemmie see your b00bs. FABO Gold Member

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        It has air trapped in the system. I always let them idle with the cap off and in the yard with a pan under it. Keep an eye on the level and when it drops, fill it up and put the cap on. The problem is air gets trapped around the thermostat and keeps it from opening. If you let it sit there and idle until the coolant drops, you are forcing the thermostat to open.
         
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        • Joey4speed

          Joey4speed FABO Gold Member FABO Gold Member

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          Remember, after the Thermostat opens, then the cycling of hot engine water into the radiator begins.
           
        • Righty Tighty

          Righty Tighty Well-Known Member

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          Thanks folks. So that makes me wonder, why wouldn't it burp into the overflow reservoir? Why would it only burp out of the top of the radiator?
           
        • dano

          dano Evil Handy Man

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          Yep, I saw this yesterday when I changes the radiator out on my car. Started it up and let it idle with the cap on fully. As it warmed up my gauge said 0 degrees. The after 10 min of idle and feeling the radiator tanks be hot I flogged the throttle to 2500 rpms and my temp need jumps to 150 then slowly rose to 180 after 5 more min.

          The scary thing was my WRX. Every time I needed to pull the radiator for work, Id fill it and the overflow and drive it for 30 min watching the temp gauge be pegged at high until it burped. It was always unnerving with an open deck aluminum block and heads.
           
        • Joey4speed

          Joey4speed FABO Gold Member FABO Gold Member

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          Inevitably it corrects itself. In my experience the closed system pressure slows that process down.
          BTW. When checking or removing hot radiator caps. Always squeeze the upper radiator hose first, if that is soft, theres little psi behind the radiator cap, and its safe to open.
          If that upper hose is hard, theres alot of psi in that radiator and WAIT to open the cap.
          Take care.
           
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          • 67Dart273

            67Dart273 FABO Gold Member FABO Gold Member

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            These girls are easy to "burp" Just take the heater hose off that is connected to the intake manifold. Fill until liquid comes out, keep the hose ready, and slam it in place and clamp it. Then fill rad and run. After it cools down, recheck coolant and adjust level.
             
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            • Joey4speed

              Joey4speed FABO Gold Member FABO Gold Member

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              Like Rusty says, running it with the cap off, lets the air pocket bubble out of the highest point.
              If the cap is on, it keeps pressure on the system and the releasing of trapped air is not as easy.
              When the cap is on all the way, the water has to build pressure to overcome the spring in the cap, as the hydro pressure builds, its pushing and absorbed into the air pockets and delays the opening of the spring in the cap.
              Normally, without air in the system the psi would overcome the spring in the cap and allow the water to trickle into the neck and drain into the reservoir, and eventually exhaust the air.
               
              Last edited: Oct 13, 2020
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              • Righty Tighty

                Righty Tighty Well-Known Member

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                You know, maybe this explains why it was running warm after the rebuild. I added coolant prior to the first start and squeezed the upper radiator hose to assist in getting the coolant into all the nooks and crannies. Of course with a flat tappet cam, break in was pretty important, so I didn't even think of the coolant. Maybe there has always been air in the system?
                 
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                • RustyRatRod

                  RustyRatRod Lemmie see your b00bs. FABO Gold Member

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                  I answered that already. There is air trapped around the thermostat causing the thermostat to remain closed.
                   
                • George Jets

                  George Jets 1967 Dart 2 Door FABO Gold Member

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                  I use the theory that the 318 takes 4 full gallons of coolant to fill the block, heads and radiator. Don't forget the coolant that goes into the heater core too.

                  So if a person only gets 3 gallons of coolant in and the radiator is full, you know it is air locked yet.

                  So yeah, figure out a way to burp the air out of the intake manifold, then get the remainder of the 4 gallons of coolant into the cooling system.

                  Breaking in your cam on first start up and don't want to mess around with trying to burp air out while it is running. Leave the thermostat out for the 20 minute cam break in and the cooling system will easily fill up. Then after it cools down put your thermostat back in and make sure all of the coolant you just drained out goes back in to fill the system, then you know it is full.
                   
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                  • famous bob

                    famous bob mopar misfit

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                    This trapper air thing can be avoided if u just raise the front of the car before filling and running it , helps the trapped air circulate out as it will go to the highest point , being the rad/cap .
                     
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                    • halifaxhops

                      halifaxhops It's going to get stupid around here! FABO Gold Member

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                      One trick I have learned years ago in the 80's is take the thermostat and drill a 1/8" hole in the flat part that is stationary, never again will it trap air.
                       
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                      • Righty Tighty

                        Righty Tighty Well-Known Member

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                        I might just try that next time.
                         
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                        • Righty Tighty

                          Righty Tighty Well-Known Member

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                          Joey4speed nailed it. I wasn’t thinking of the spring in the cap needing to be depressed in order to allow coolant to flow into the reservoir. I’m kinda slow, sometimes folks need to spell things out like I’m 5. And then explain it again. Lol
                           
                        • Righty Tighty

                          Righty Tighty Well-Known Member

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                          This morning when I started up the car to leave work, I removed the cap and let it idle. Got up to 190*, then it backed down just a hair, then back up to 190*. I watched the filler neck for bubbling or burping or any activity. Nothing except a bit of steam coming off the hot coolant. The level remained the same at full. Drove it home and the temp hovered around 210. How long should I expect it to take for the air to be expelled? I'll give it another go now that I'm home and can take a little more time.

                          At any rate, I've got bigger fish to fry. I noticed a ticking from the driver side valve cover and it sounds like I've got a cylinder missing. oh boy.
                           
                        • Righty Tighty

                          Righty Tighty Well-Known Member

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                          Okay. Let it idle in the driveway for a bit, the coolant level rose slightly several times and flowed into the reservoir, temp held exactly at 190. Decided to shut it down and attempt to diagnose the ticking/dead cylinder. While I was waiting for it to cool a bit, decided to squeeze the upper rad hose. Burped out some air, but more interestingly, a chunk of material appeared. After some fishing, I tweezed out a piece of black RTV that must have dislodged itself from the intake. Maybe that was restricting the flow through the thermostat, and by squeezing repeatedly I got it to flow through into the radiator?

                          Anyhow, on to the tick. Removed the driver side valve cover an BAM. Right away I found a collapsed #1 intake lifter. Hopefully that is all that is wrong.
                           
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                          • Righty Tighty

                            Righty Tighty Well-Known Member

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                            Here’s today’s catch!

                            image.jpg
                             
                          • Righty Tighty

                            Righty Tighty Well-Known Member

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                            Cam is ruined.

                            980298EF-FD37-4D08-9C46-3D3F3A030DA7.jpeg
                             
                          • DrCharles

                            DrCharles Well-Known Member

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                            Ouch!
                            Are you going to take the whole engine down, or change the oil a couple of times and put new bearings in?
                             
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