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Drilling holes in thermostats...how many?-gctid810156

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    Drilling holes in thermostats...how many?-gctid810156

    I have a 2011 Ciera 2855 Bravo III Merc 350. I'm replacing the thermostat today. Some suggest drilling a 1/8 inch hole in the lip.

    Avoiding the argument whether a person should do this or not, IF one decides to do so, how many holes are suggested???

    Thanks

    Mike

    #2
    2 pcs 1/8" holes - this will make sure the manifolds get some cooling even when the thermostat is closed.....

    /MOL
    Mogens Olesen
    Bayliner 2855 Ciera Sunbridge ST (1998)
    7.4 L MPI Mercruiser (1998) with full closed cooling
    Bravo 3 Duo prop drive (1998)

    Comment


      #3
      Most thermostats have a small hole in then ir a notch for the sole purpose of letting the air bleed out. The water manifold system cools the manifolds with a bypass arrangement. The t-stat opening diverts a portion of water thru the engine when needed. The manifolds are AWAYS being cooled or the rubber couplers would burn.

      Opening holes in the t-stat may cause the engine to run too cool at idle.
      Captharv 2001 2452
      "When the draft of your boat exceeds the depth of water, you are aground"

      Comment


        #4
        Captharv - I don't agree in your statement.

        If you have full cloosed cooling system (including exhaust manis & 3"/6" spacers) - the raw Water will enter the knees and cool the knees and the rubber couplers. and yes this always take place.

        What doesn't take place is the cooling of the exhaust manis & spacers before the T-stat opens - as soon as it opens the full flow of glycol (from the engine) is being passed through the exhaust manis & spacers ending up in the tubular heat exchanger - being cooled Down and fed back to the engine Again.

        By making 2 1/8" holes in the T-stat - there will always enough flow to the exhaust manis and spacers - even with closed T-stat.

        The T-stat supplied with/to a full closed cooling system already has theese 2 bleed holes pre-drilled.

        /MOL
        Mogens Olesen
        Bayliner 2855 Ciera Sunbridge ST (1998)
        7.4 L MPI Mercruiser (1998) with full closed cooling
        Bravo 3 Duo prop drive (1998)

        Comment


          #5
          Look at this thread (ignore the wrong terminology "fresh Water cooling" - it is a full cloosed cooling system I have.

          http://www.baylinerownersclub.org/in...7-4-l-mpi-1998

          /MOL
          Mogens Olesen
          Bayliner 2855 Ciera Sunbridge ST (1998)
          7.4 L MPI Mercruiser (1998) with full closed cooling
          Bravo 3 Duo prop drive (1998)

          Comment


            #6
            Well I drilled two 1/8 inch holes in the thermostat and my temperature on the gauge has never been better. Checking the engine with my IR gun proved to be also good.

            Thanks for the idea.

            Mike

            Comment


              #7
              No - not correct I am afraid - the exhaust manifolds will not get anything before the T-stat opens!

              /MOL
              Mogens Olesen
              Bayliner 2855 Ciera Sunbridge ST (1998)
              7.4 L MPI Mercruiser (1998) with full closed cooling
              Bravo 3 Duo prop drive (1998)

              Comment


                #8
                And here then explanation in a Picture why you are wrong CAPTHARV

                [attachment=37193]ClosedCoolingschematicforMOL4[1].jpg[/attachment]

                The green arrows indicate the flow of ethylene glycol coming from the T stat housing (when it is open!)

                The blue arrows indicates the seawater flow - and is always present independant of then T stat !

                I hope this clarifies it.

                /MOL


                Attached files

                Mogens Olesen
                Bayliner 2855 Ciera Sunbridge ST (1998)
                7.4 L MPI Mercruiser (1998) with full closed cooling
                Bravo 3 Duo prop drive (1998)

                Comment


                  #9
                  Mine is an old boat, so it may be different. there are hoses leading from the tstat housing to the exhaust jackets. water flows to these exhaust jackets as soon as the engine fires up. I pulled on and found out the hard way..... spllsh splash...



                  Attached files

                  1987 Bayliner Ciera Sunbridge 2150.
                  May your portapot not tip over in 5 foot seas.......

                  Comment


                    #10
                    The reason you drill holes in thermostats is not unique to boats. They are there to provide a small amount of flow of warming water across the the wax pellet so it melts smoothly and at the right temp. This bypasses a bit of coolant and allows air pockets to clear. This is true in raw water cooled or closed loop ethylene glycol cooled boats as well.
                    Custom CNC Design And Dash Panels

                    iBoatNW

                    1980 CHB Europa 42 Trawler- "Honey Badger"

                    Comment


                      #11
                      Just to clarify - a closed full cooling system has a different flow Circuit than a raw Water cooled system. This is why the T stat housing is changed when installing a closed full cooling system.

                      My statements are related to a closed full cooling system - and I am certain they are correct.

                      A raw Water cooled engine has a constant flow of seawater through the exhaust manifolds (and extensions if present) - which also cools the knees and is expelled in the exhaust pipe (to cools the rubber couplers etc.)

                      This is NOT the case if the engine is with a closed full cooling system!

                      EG is circulated in the engine block until the T stat opens up the flow of EG to the exhaust manifolds. This is why the 2 1/8" bleed holes are quite important in a cloosed cooled full system.

                      Note that raw Water/sea Water ALL the time is expelled in the exhaust pipe - it has nothing to do with the T stat in a closed cooled full system.

                      /MOL
                      Mogens Olesen
                      Bayliner 2855 Ciera Sunbridge ST (1998)
                      7.4 L MPI Mercruiser (1998) with full closed cooling
                      Bravo 3 Duo prop drive (1998)

                      Comment


                        #12
                        Captharv is correct...

                        Mercruiser utilized a full flow thermostat housing that direct flow through the heat exchanger or through the bypass circuit at all times. This is a key feature of Mercruiser Cooling System in that regardless of the thermostat position, the engine always experiences 100% coolant flow.

                        My engine can take up to 20-30 minutes for the thermostat to reach 160┬░ to open warming up slow.

                        Can't imagine hot exhaust gas passing through the manifolds for 20 minutes with no cooling :whistle:
                        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


                          #13
                          The P.O. of my boat changed the thermostat at some point and did not drill the 2 1/8" holes. Therefore no coolant flow to the manifolds and spacers until the stat opened up. Luckily I bought the boat and just decided to change the thermostat for preventive maintenance reasons and caught that. Whether or not it will do damage to anything I don't know. But they should be there. The right thermostat would come with the system when you buy it but after that who knows who has been working on it.
                          Doug
                          1995 2859 -extensively rebuilt/restored 2016/17
                          496 big block - Bravo ll leg
                          The Doghouse
                          Prince George BC

                          Comment


                            #14
                            Hi Sketch96 - glad you caught it! The 2 pcs 1/8" bleeding holes in the T stat ensures that a tiny flow of EG is always present to the exhaust manifolds - even when the the T stat is closed.

                            Also thanks for supporting me here - I know what I say is correct but somehow the Guys above doesn't seem to believe it.

                            I investigated this matter very very thoroughly when I installed my San Juan full closed cooling system (MC-330) - I even contacted San Juan to make sure I understod the system correct - and yes the 160F T stat supplied with the system indeed had the 2 1/8" bleeding holes !

                            Maybe Mercruiser has a special T stat housing that has a small bleeding channel built into it - never seen it though? The ones I have seen from Mercruiser also needs 2 bleeding holes.

                            Ruffryder - the heating up period was exactly my concern as well - and was the reason I contacted San Juan to ensure the manifolds got the needed cooling when the T stat was closed. The two bleeding holes takes care of this!

                            /MOL
                            Mogens Olesen
                            Bayliner 2855 Ciera Sunbridge ST (1998)
                            7.4 L MPI Mercruiser (1998) with full closed cooling
                            Bravo 3 Duo prop drive (1998)

                            Comment


                              #15
                              Sounds like San juan guys have no idea what they are doing...just because some sales guy told you over the phone, makes it right?

                              actually think those 2 1/8th bleed holes is going to cool down your exhaust system? inch:

                              Best way to burn down those rubber exhaust shutters stuff em down the Y pipe.

                              Shouldn't have to back yard Jerry rig your thermostat...the system wasn't designed intended to be like that.

                              Like I said...key feature of Mercruiser Cooling System in that regardless of the thermostat position, always experiences 100% coolant flow.

                              https://www.perfprotech.com/mercruis.../category/1287

                              Read what it says in the middle of the page,

                              Full flow coolant flow strategy which means thermostat bypassing is not utilized thereby ensuring FULL COOLANT FLOW THRU THE EXHAUST SYSTEM, as well as desirable operating temperatures when idling in cold water conditions.

                              This is the proper OEM kit & proper installation.

                              Technology has been changed...

                              Yes we use a special full closed thermostat housing with no thermostat in it, this way it ensures full coolant flow thru the exhaust system.

                              Thermostat is located on the HEAT EXCHANGER, with bypass passage as always...this ensures full coolant flow thru the engine.

                              https://youtu.be/LcXXnV_Rn24

                              https://youtu.be/4hdaCvcA8pc

                              I think I've explained enough...
                              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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