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  • BlackBird58
    Experienced
    • Mar 9 2005
    • 102

    coolant overflow at high rpm?

    I've made some upgrades to the cooling system of my '58 bird (w/61 390) and I'm still having problems. In the last two weeks, I did a chemical flush of the cooling system (60 min acid cleaner, 10 min neutralizer, 5 min pure water, then refill with coolant/water mix) and I also installed a hayden 7 blade flex fan. No shroud yet.

    Now, the system seemed to stay cool and sealed until I get the engine much over 2500 rpm. At that point the radiator begins to boil over all around the overflow tank cap. Once it starts it keeps boiling until the engine is cool again. Today on my way to work I lost about a gallon of coolant over about 30 miles of driving. I topped off the coolant before driving home, and carefully kept under 2500 rpm. Temp was fine and no boil over.

    What is going on here? I know there is still scale and rust in the cooling system, as the waterpump inlet to the heater still has lots of junk in it. Do I need to flush the system again? Is my fan belt too tight? Is this a symptom of a more serious problem?

    I appreciate the help!

    Mel




  • byersmtrco
    Super-Experienced
    • Sep 28 2004
    • 1839

    #2
    RE: coolant overflow at high rpm?

    Sounds like the radiator core is partially plugged. Typical for the age of the motor. My old 390 did it. Had a new core put in. Within 6 months it was plugged again. Just all the rust in the engine. Those chemical flushes are maintenence only. They only keep it clean, not remove 40 years of build up. Can't hurt though. The flex fan will help the slow speed. After 30 mph, fan doesn't matter. The flexfan will cause less drag on the motor. Get that radiator looked at. I had mine made into a 4 row this last time. Get that shroud !! I'm tellin ya !! It's about 100 bucks from Dearborn Classic. For the moment too, as a test, by-pass the heater core. that could be plugged causing some restriction.

    John

    Comment

    • BlackBird58
      Experienced
      • Mar 9 2005
      • 102

      #3
      RE: coolant overflow at high rpm?

      It's definitely possible that the core is partially plugged. I've already got the heater core bypassed as it was leaking.

      You mention that the chemical flushes can't remove all the years of build up. Is there anything that will remove it? The '58 service manual mentions a pressure flush but warns that it could cause leaks.

      I'll really like to get the engine as clean as possible before I spend to repair the radiator!

      Thanks,
      Mel


      Comment

      • Guest

        #4
        RE: coolant overflow at high rpm?

        Keep in mind too that water expands when heated........cars today have water exiting the radiator cap into an overflow tank. When the car cools down........it is sucked back into the engine. Our birds dont have this. Next time you fill it........leave 2 or 3 inches from the top of the expansion tank.

        Comment

        • Guest

          #5
          RE: coolant overflow at high rpm?

          hi
          It is also possible that the head gasket is slightly blown causing the compresion to blow back into the cooling system forcing the water out. at a low rpm the tank would be able to vent of the pressure but as your engine speed increases it would not be able to keep up. Sometimes you can spot this with excessive air bubles in the tank but not always as there seems to be bubbles anyhow. If that is the problem it will get progressively worst, i hope that is not it. some times you can find moisture on 1 of the plugs / cyl. to clue you in but not always as if the leak is slight it will dry out. good luck
          later
          Mark, 60 conv.

          Comment

          • BlackBird58
            Experienced
            • Mar 9 2005
            • 102

            #6
            RE: coolant overflow at high rpm?

            Are there any other tests I can do to determine if it's the head gaskets? Would a compression test help?

            Comment

            • Guest

              #7
              RE: coolant overflow at high rpm?

              My vacuum gauge instructions say that if the needle flucuates between a high and a low point, then most likely you have a leaking head gasket and need to perform a compression test. The compression manual claims that a 20 lb difference between 2 adjacent cylinders indicates a probable leaking head gasket.

              Comment

              • byersmtrco
                Super-Experienced
                • Sep 28 2004
                • 1839

                #8
                RE: coolant overflow at high rpm?

                They can do a pressure test . . . Or that vac test. Typically with this engine, if there is a head gasket problem, you'll get inter-mix. That means clnt in the oil and vissa versa. The oil will look like a choc milkshake. Bubbles in the tank could mean that as well. I'd still bet on a clogged core. 1st step, have a radiator guy chk it.


                JB

                Comment

                • BlackBird58
                  Experienced
                  • Mar 9 2005
                  • 102

                  #9
                  RE: coolant overflow at high rpm?

                  Well, I've definitely got the chocolate milkshake boilover. I'll check the radiator, the compression and the engine vacuum; hopefully I don't have a blown gasket!

                  Thanks,
                  Mel

                  Comment

                  • byersmtrco
                    Super-Experienced
                    • Sep 28 2004
                    • 1839

                    #10
                    RE: coolant overflow at high rpm?

                    What does the engine oil look like? Have em do a pressure test.

                    Comment

                    • ayrwoof
                      Experienced
                      • Apr 4 2005
                      • 100

                      #11
                      RE: coolant overflow at high rpm?

                      Yes snap -on sells a combustion gases test for radator ive used it at work . it does detect a leaking head gasket/// dave

                      Comment

                      • ayrwoof
                        Experienced
                        • Apr 4 2005
                        • 100

                        #12
                        RE: coolant overflow at high rpm?

                        ps dont go back together stupid ,with these engines. get a thick
                        flat metal plate add 100# grit sand paper to it and sand off the
                        high spots on the heads and the block too then hose off ///

                        Comment

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