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Closed cooling thermostat housing gasket and thermostat replacement

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    Closed cooling thermostat housing gasket and thermostat replacement

    Last season I had some issues getting my engine coolant gauges to read... they would intermittently go dead on me... both helms. Did all the standard troubleshooting to determine the sensor was ok, as well as both gauges were ok. Then, as a last resort I decided to slightly loosen the bolts holding the housing sections to the block, not enough to break the gasket seals, then tighten then back up again. This fixed the problem for a while.... so I guess my issue is with grounding. Decided to take it all apart for a cleanup and new gaskets and thermostat. I didn't know what I needed in advance, but my local parts guy sold me various gaskets for the different sections of the housing as well as the new thermostat, thermostat gasket and a little plastic insert that he wasn't sure if I'd need or not.

    As far as I can tell... my thermostat fit into the recess in it's part of the housing, but when I used the cork gasket I got for it didn't... with the gasket, the thermostat sat proud of the surface and actually interfered with the main gasket between the thermostat housing section and the section above. So, I've installed it without the cork gasket. All of this probably makes not a lot of sense without the pics... so see below for more detail. I'm wondering if I should have made more effort to use the thermostat gasket... maybe it would have squeezed down when I tightened the bolts. As it is, everything is now working fine again with my temp gauges... and I have no leaks.

    Tyson, Ackerley, Sidney & Gene
    Tsawwassen, BC
    1996 2858 Ciera Command Bridge
    Mercruiser 7.4L BRAVO II (GEN. V) GM 454 V-8; Engine Serial 0F603347
    "Island Passport"
    Home marina: Point Roberts, WA

    #2
    In my opinion, the temp sensor should be in the intake manifold where it can read coolant temp prior to the coolant exiting the thermostat.
    However, if that’s OEM, then yes..... your issue was the housing not making a good connection to Negative.

    Try removing any paint from where one of the bolt heads makes contact to the housing. Also, install a star washer under the head of that bolt.


    .
    Rick E. Gresham, Oregon
    2850 Bounty Sedan Flybridge model
    Twin 280 HP 5.7's w/ Closed Cooling
    Volvo Penta DuoProp Drives
    Kohler 4 CZ Gen Set

    Comment


    • Nauti_Mike
      Nauti_Mike commented
      Editing a comment
      The sendor is under the t-stat so it is before exiting, however I would prefer it be in the intake as well. Mercruiser does this on lots of there setup and return connection becomes problematic. I think they do this because the intake typically only has one port and there are two sendors; temp switch and temp sendor. This also leaves the intake port for a water heater connection.

    #3
    As Rick said a good connection via the bolt head will ensure a solid negative connection.
    Rick, I belive his t-stat sits between the two halves of that crazy housing. If that’s the case then both the temp switch and sender would be located “upstream” of the t-stat. It also appears that there is a coolant supply in that lower half as well so he should have some coolant flow prior to the t-stat opening.
    Dave
    Edmonds, WA
    "THE FIX"
    '93 2556 5.7 Bravo II 2.0:1 18 1/4x19 P
    (.030 over-Vortec top end-part closed cooled)
    The rebuild of my 2556 https://www.baylinerownersclub.org/f...76?view=thread
    Misc. projects thread
    https://www.baylinerownersclub.org/f...56-gctid789773

    Comment


      #4
      Thanks Rick,

      My issue was solved by replacing the gaskets...The gasket I was provided for use between the lowest section and the engine block had 4 metal grommets in it to provide continuity between the housing and the block. This lowest section of this aftermarket setup does contain the thermostat and under the thermostat just above the engine block opening are the sensors, so you are correct.

      My question was more around have I screwed up by NOT using the cork gasket that fits into the machined recess where the thermostat sits. As far as I can tell it didn't have one previously... but things were so deteriorated, even the normal gaskets, that it was hard to tell. As I said, it's not leaking at idle, nor when I run it up to higher RPMs. Just want to be sure I've not missed something standard.

      Tyson, Ackerley, Sidney & Gene
      Tsawwassen, BC
      1996 2858 Ciera Command Bridge
      Mercruiser 7.4L BRAVO II (GEN. V) GM 454 V-8; Engine Serial 0F603347
      "Island Passport"
      Home marina: Point Roberts, WA

      Comment


        #5
        the narrow cork gasket is to insure the thermostat sets snuggly in the groove and doesnt allow water to pass around it... its not usually needed in most applications because the "reliefs" that are cut in for the thermostat to set in are shallow enough that the housing gasket will clamp against the thermostat when the housing bolts are tightened....

        from your description its unlikly that you need it, or that it would even fit correctly if you tried to use it... if the relief is a bit deeper than normal, a thin line of silicone in the relief before setting the thermostat in will accomplish the same thing.

        some applications have the relief cut deeper because they are meant to have a rubber seal fitted around the outer edge of the thermostat, and this is the only seal used. no gasket... the cork ring can be used in place of the fitted rubber edge seal in this type of application...


        NU LIBERTE'
        Salem, OR

        1989 Bayliner 2556 Convertible
        5.7 OMC Cobra - 15.5x11 prop
        N2K equipped throughout..
        2014 Ram 3500 crew cab, 6.7 Cummins
        2007 M-3705 SLC weekend warrior, 5th wheel
        '04 Polaris Sportsman 700 -- '05 Polaris Sportsman 500 HO
        Heavy Equipment Repair and Specialty Welding

        Comment


        • tdcooper99
          tdcooper99 commented
          Editing a comment
          Thanks for the affirmation. That relief for the 'stat to set into was exactly the depth for it to sit perfectly flush... and yes, once the next section sits on top, it actually prevents it from moving. My feeling is had I tried to use the cork gasket I would have put a lot of stress on the edge of the thermostat and maybe wouldn't have got the housing to seal properly.... at least not without over torquing the 2 bolts and risking stripping them.

        #6
        Yea, your good to go
        Dave
        Edmonds, WA
        "THE FIX"
        '93 2556 5.7 Bravo II 2.0:1 18 1/4x19 P
        (.030 over-Vortec top end-part closed cooled)
        The rebuild of my 2556 https://www.baylinerownersclub.org/f...76?view=thread
        Misc. projects thread
        https://www.baylinerownersclub.org/f...56-gctid789773

        Comment


          #7
          Thanks for all your responses. Always good to have affirmation.
          Tyson, Ackerley, Sidney & Gene
          Tsawwassen, BC
          1996 2858 Ciera Command Bridge
          Mercruiser 7.4L BRAVO II (GEN. V) GM 454 V-8; Engine Serial 0F603347
          "Island Passport"
          Home marina: Point Roberts, WA

          Comment


            #8
            They used to supply with a thinner rubber O ring I believe...
            Joon, Kathy, Jaden & Tristan
            Uniflite 42 AC, DD 671N
            93 3058 sold
            92 2855 (day boat)
            91 Fourwinns 205 (lake boat)
            Longbranch WA
            Life is Good

            Comment

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