C4 Cooling System Bleeding - NCRS Discussion Boards

C4 Cooling System Bleeding

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  • Jim P.
    Frequent User
    • February 25, 2010
    • 58

    C4 Cooling System Bleeding

    Hi all this is probably addressed somewhere but I haven't found it. Trying to bleed the cooling system on my 1994 LT1, but either I am not opening the screws far enough or not leaving them open long enough. About how many turns should you open them and about how long does it take before coolant starts to come out? Does it usually come out of the throttle body bleeder or the thermostat bleeder first? Because this may affect your answer I drained the radiator and got the knock sensor out on the passenger side but I couldn't get the one on the drivers side out. In total I drained a little more than 2 gallons of coolant.

    Thanks.
  • Keith B.
    Extremely Frequent Poster
    • September 15, 2014
    • 1581

    #2
    Re: C4 Cooling System Bleeding

    start the car with the radiator cap off. once the t-stat opens any air trapped will burp out

    Comment

    • Jim P.
      Frequent User
      • February 25, 2010
      • 58

      #3

      Comment

      • Keith B.
        Extremely Frequent Poster
        • September 15, 2014
        • 1581

        #4
        Re: C4 Cooling System Bleeding

        I never did in the ten years and dozen or so times I've worked on my cooling system in my old 94

        Comment

        • Jim P.
          Frequent User
          • February 25, 2010
          • 58

          #5
          Re: C4 Cooling System Bleeding

          Sounds a lot easier. Thanks

          Comment

          • Mark E.
            Extremely Frequent Poster
            • April 1, 1993
            • 4529

            #6
            Re: C4 Cooling System Bleeding

            I open the bleeder valve on the thermostat housing, fill until coolant comes out, quickly close the bleeder, then continue filling. After the engine has run with the thermostat open, let it cool then check the level and topoff as needed.

            If you can't remove one knock sensor, flush out from the other sensor and radiator peacock until clear, close up and fill, run until the thermostat opens then repeat the cycle until clear. I recommend Evapo-Rust Thermocure.
            Mark Edmondson
            Dallas, Texas
            Texas Chapter

            1970 Coupe, Donnybrooke Green, Light Saddle LS5 M20 A31 C60 G81 N37 N40 UA6 U79
            1993 Coupe, 40th Anniversary, 6-speed, PEG 1, FX3, CD, Bronze Top

            Comment

            • Jim P.
              Frequent User
              • February 25, 2010
              • 58

              #7
              Re: C4 Cooling System Bleeding

              Thank you Mark. Approximately how many turns to open the bleeder valve at the thermostat? I am concerned about getting it so loose that it pops out. Also you don't bleed the throttle body screw at all? Thanks for your help.

              Comment

              • Matthew T.
                Frequent User
                • April 6, 2022
                • 38

                #8
                Re: C4 Cooling System Bleeding

                Bleed screws locations are both #2's
                Attached Files
                Last edited by Matthew T.; January 3, 2023, 09:46 AM.

                Comment

                • Jim P.
                  Frequent User
                  • February 25, 2010
                  • 58

                  #9
                  Re: C4 Cooling System Bleeding

                  Thanks Matthew this is very helpful.

                  Comment

                  • Mark E.
                    Extremely Frequent Poster
                    • April 1, 1993
                    • 4529

                    #10
                    Re: C4 Cooling System Bleeding

                    Less than 1 turn to open.

                    I've found only opening the single bleeder does the job.
                    Mark Edmondson
                    Dallas, Texas
                    Texas Chapter

                    1970 Coupe, Donnybrooke Green, Light Saddle LS5 M20 A31 C60 G81 N37 N40 UA6 U79
                    1993 Coupe, 40th Anniversary, 6-speed, PEG 1, FX3, CD, Bronze Top

                    Comment

                    • Brad Hillhouse (37766)

                      #11
                      Re: C4 Cooling System Bleeding

                      Pro Tip -

                      Put a rag or paper towels in behind the waterpump and under the bleeders while opening the bleeder valves.
                      The output hole may be pointing in a way that sprays coolant directly behind the waterpump and onto the opti.

                      You don't forget lessons learned the hard way.....

                      Brad


                      20220707_120515.jpg

                      Comment

                      • Joe L.
                        Beyond Control Poster
                        • February 1, 1988
                        • 43211

                        #12
                        Re: C4 Cooling System Bleeding

                        Originally posted by Brad Hillhouse (37766)
                        Pro Tip -

                        Put a rag or paper towels in behind the waterpump and under the bleeders while opening the bleeder valves.
                        The output hole may be pointing in a way that sprays coolant directly behind the waterpump and onto the opti.

                        You don't forget lessons learned the hard way.....

                        Brad


                        [ATTACH=CONFIG]115118[/ATTACH]
                        Brad------


                        Yes, this is critically important for any LT1 or LT4 but especially critical for 1992-94.

                        In addition, a leaking waterpump, even at the early stages of leakage when it might not be readily apparent, can have disastrous consequences for the Optispark distributor.
                        In Appreciation of John Hinckley

                        Comment

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