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Nylon Balls

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  • Nylon Balls

    Can anyone tell me what the purpose of the nylon balls inside the thermostat housing is.


  • #2
    Re: Nylon Balls

    Restrict the amount of flow going to the manifolds and risers, so there is enough water to cool the engine when needed.
    In later models, without the balls, there are drilled passages of the correct size.
    Don S.

    Please, no PM's (Private Messages) regarding boat/engine problems.
    That is what the forums are for.
    Only forum/moderator issues will be answered in PM's.


    • #3
      Re: Nylon Balls

      When the thermostat is closed, the water exits through the check ball outlets, then flows to the risers, skipping the exhaust manifolds. When the thermostat opens, the check balls provide some back pressure to push water through out the block and out the non-check ball outlets. These are typically plumbed to the exhaust manifold. You NEED the check balls to get good flow through the block.
      In later years, Mercruiser redesigned the thermostat housing to eliminate the need for the check balls...

      OOPS I didnt see you answered Don.

      1969 StarCraft Chieftain, 4.3 Mercruiser Alpha One Gen II

      Link To Restoration Page


      Its What I Don't Say You Should Be Worried About...


      • #4
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        Re: Nylon Balls

        Thanks guys this is just a preview of my next post "overheating troubles"