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5.0L Merc port side exhaust hotter

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    5.0L Merc port side exhaust hotter

    I replaced the thermostat on my 5.0 Mercruiser carbureted engine (165 degree) and I have noticed that the port side exhaust runs hotter than the starboard side. Its not burning my hand, I can hold my hand on the down elbow a for like 10 seconds, but the other side feels almost ice cold in comparison.

    I read somewhere, this is somewhat normal but I wanted to see if there is anything I should check out, just in case?

    For example, the ball valves in the T pipe looked ok, but I did not replace those. Should I?

    This is a fresh water boat with, raw water cooling.

    Anyone seen this before?
    2003 Runabout 205BR (bowrider) Merc 5.0, Alpha 1 Gen 2

    #2
    If raw water cooled I think you have the wrong tstat, it should be 140*.
    Don
    1995 Maxum 2400 SCR LUNA DE MIEL
    1988 Bayliner 2455 (sold)
    1976 Tahiti 16.5 I/O (sold)
    10 ft livingston (lost in fire )
    1987 18ft. Seaswirl cuddy (lost in fire)
    "Is it better to be on a boat thinking about God, or be in church thinking about boating?"

    Comment


      #3
      Common for one side to be hotter, get an IR temp sensor and get real readings to know if an issue exits.
      1997 Maxum 2400 SCR 5.7LX Bravo II

      Mike

      Comment


        #4
        Agree with Don 140 if raw water cooled 160 if closed cooled. Change your t stat then check your temps again. Often at idle rpm one side can run a touch warmer than the other, bump your rpm up somewhere around 1000 then check it again. You’ll likely feel a decrease in temp on that side. May be time for a new impeller.
        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

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          #5
          The TStat I removed was the original and was stamped build year 2002 and 160 deg from the factory. All the info from the mercruiser service center says its supposed to be 160 too.

          I also just replaced the impeller, seals, housing, etc this winter. Its carbureted and not EFI, if that helps.

          I'll temp gun it this weekend and see the difference in different spots, and report back the info.
          2003 Runabout 205BR (bowrider) Merc 5.0, Alpha 1 Gen 2

          Comment


          • builderdude
            builderdude commented
            Editing a comment
            If used in lake/river water only the 160 would be ok for a raw water cooled engine.

          #6
          Fresh water boat ...

          Last time elbows were took off and the ports looked at ?

          Start with the hotter one first.

          Last time impeller changed in the drive ? I use a complete kit housing and all.
          Be good, be happy, for tomorrow is promised to no man !

          1994 2452, 5.0l, Alpha gen. 2 drive. Sold ! Sold ! Sold !

          '86 / 19' Citation cuddy, Merc. 3.0L / 140 hp 86' , stringer drive. Sold ! Sold ! Sold !

          Manalapan N.J

          Comment


            #7
            ......................
            Originally posted by raspeitia View Post
            I replaced the thermostat on my 5.0 Mercruiser carbureted engine (165 degree) and I have noticed that the port side exhaust runs hotter than the starboard side. Its not burning my hand, I can hold my hand on the down elbow a for like 10 seconds, but the other side feels almost ice cold in comparison.
            The engine's thermostat is upstream of any division of "spent" seawater, therefor it cannot be responsible for incorrect division of "spent" seawater.
            (spent seawater = seawater that has cooled the engine and is now on it's way to the exhaust system)


            I read somewhere, this is somewhat normal but I wanted to see if there is anything I should check out, just in case?
            A slight deviation in temperature between Port and Starboard exhaust elbows is acceptable.
            Anything beyond that is NOT acceptable, and will indicate a spent seawater restriction.


            For example, the ball valves in the T pipe looked ok, but I did not replace those. Should I?
            I hate those silly things. No other company uses them.
            Merc says to leave them and/or replace them.


            This is a fresh water boat with, raw water cooling.

            Anyone seen this before?
            Oh yes..... this is quite common!
            find the restriction, and things should return to normal.


            Remove both exhaust Elbows. Look closely at the seawater transfer ports.
            Clean/clear them from any rust scale.
            Also look closely at the port(s) that supply seawater into the mixing chamber.


            You may also want to remove the T-stat housing and look for a rust scale caused restriction.
            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


              #8
              Originally posted by raspeitia View Post
              .................All the info from the mercruiser service center says its supposed to be 160 .
              Just to clarify......
              raw water cooled engine:

              .... lake or river water...... 160 is OK
              .... ocean water....... 160 is too high, and will accelerate Salt Water Crystallization.


              .


              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


                #9
                Thanks everyone. I appreciate all the extra knowledge and for all the detailed responses.

                When I last checked it while under power, the intake and return hoses from the manifolds seemed about the same temperature. I'll make sure to temp gun those though.

                I removed both manifolds this winter to replace the exhaust gaskets where they mount to the block and it looked nice and clean.

                I did see little bits in the drain port when I winterized it last fall though, so there definitely is something there but not a lot from what came out.

                I'll pull the hoses and see if there is anything in the channels on that side before I go out next time.

                2003 Runabout 205BR (bowrider) Merc 5.0, Alpha 1 Gen 2

                Comment


                  #10
                  ................
                  Originally posted by raspeitia View Post
                  I removed both manifolds this winter to replace the exhaust gaskets where they mount to the block and it looked nice and clean.
                  The areas of concern will be the seawater transfer ports that are between the manifold and elbow.
                  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


                    #11
                    Also look at the outlet ports on the hot side elbow, (inside of where the exhaust hose slides over the elbow exit), flakes of rust can clog them.
                    88 Four Winns 200 Horizon 4.3 OMC
                    98 Jeep Grand Cherokee 4.0/Selectrac
                    07 Jeep Grand Cherokee 5.7 Hemi/Quadradrive II

                    Long Island Sound Region

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