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  • Leaking Thermostat

    I have a 2003 Merc/Yamaha 225 4 stroke. the Merc model number is # 1225F234K that I recently purchased used. In going over the engine I discovered (maybe too late?) that water is leaking from the port side thermostat housing. It appears that the rubber gasket has been squeezed or pushed out.

    Has anyone ever experienced this problem before? I have ordered replacement thermostast but am wondering is this is a sign of a much deeper problem.

    Also, when I go to replace the thermostat will I have to pull off the intake manifold or is it possible to replace them with in place. Clearly I would like to avoid removing the intake manifold if possible, less things to drop of parts to lose

  • #2
    Early Yamaha F200/F225 thermostat housings have been known to corrode from the inside out. Remove the thermostat and using a bright light inspect the interior of the housing/bore.

    Hoprefully, your motor has a failed thermostat seal but this is very unlikely.

    Go to simyamaha.com and then to service information and on to F225 information. A removal and replacement procedure is there. No need to pull an intake manifold as I recall.

    Comment


    • #3
      LOL
      it sure LOOKs like you need to remove the intake manifold,

      but it actually can be done with fairly minimal disruption,

      You can get at one or two housing bolts with a socket, but you'll need a 10 mm open end or box wrench for the others



      The corrosion I've seen was on the block side of the thermostat, behind the gasket.

      The gasket "squeezing out" doesn't sound good, though.....

      Comment


      • #4
        Originally posted by boscoe99 View Post
        Early Yamaha F200/F225 thermostat housings have been known to corrode from the inside out. Remove the thermostat and using a bright light inspect the interior of the housing/bore.

        Hoprefully, your motor has a failed thermostat seal but this is very unlikely.

        Go to simyamaha.com and then to service information and on to F225 information. A removal and replacement procedure is there. No need to pull an intake manifold as I recall.
        As I feared, there is a dark side to this discovery. Do you know of any methods to correct or finesse a corrosion problem short of machining or a new block?

        Comment


        • #5
          port side.
          simply remove the ISC housing.
          access the castings, figure out how bad it is.
          go from there.
          remember there isn't much pressure on that side of the T stat.

          Comment


          • #6
            Leaking Thermostat

            Thanks. Assuming is is not too bed, is there an epoxy of similar material you would recommend for patching?

            Comment


            • #7
              JB Weld for aluminum.

              Thermostat sits inside a cavity in the block. Thermostat is comprised partly of copper. Copper is death to aluminum. Is it the copper being influenced by a saltwater electrolyte that is causing/contributing to the problem?

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              • #8
                [QUOTE=fairdeal;107715]LOL
                it sure LOOKs like you need to remove the intake manifold,

                but it actually can be done with fairly minimal disruption,

                You can get at one or two housing bolts with a socket, but you'll need a 10 mm open end or box wrench for the others



                The corrosion I've seen was on the block side of the thermostat, behind the gasket.

                The gasket "squeezing out" doesn't sound good, though.....[/QUOTE

                Looks can be deceiving.

                Comment


                • #9
                  Originally posted by boscoe99 View Post
                  JB Weld for aluminum.

                  Thermostat sits inside a cavity in the block. Thermostat is comprised partly of copper. Copper is death to aluminum. Is it the copper being influenced by a saltwater electrolyte that is causing/contributing to the problem?
                  I agree, the little bit of copper in thermostat is a major contributer to this happening. I think pulling stat and cleaning the area every year would help get rid of some of the bridging of corrosion to the copper and may help prevent a major part of it eating things up.

                  I found a pin hole on the block at the stat on my C40. I cleaned corrosion up and ended up with a good sized hole. Had it welded from out side but filled the creator hole on the inside with JB marine for aluminum, and shaped with a knife and files after it set up.
                  all is well for now anyway

                  Comment


                  • #10
                    Never could figure out why VST is not made out of a polymer plastic material. Due to nature of ethanol and water corroding the aluminum. Cheaper, lighter, and more resistant to corrosion.After all, they make gas tanks and fuel pumps out of the stuff??

                    Comment


                    • #11
                      Originally posted by Nautical View Post
                      Never could figure out why VST is not made out of a polymer plastic material. Due to nature of ethanol and water corroding the aluminum. Cheaper, lighter, and more resistant to corrosion.After all, they make gas tanks and fuel pumps out of the stuff??
                      Seems you are the only one talking about a VST tank on this thread.
                      why is that

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                      • #12
                        I was making a leap in referencing dissimilar metal corrosion as mentioned above with the thermostat housing. I have seen much corrosion inside aluminum VST and the thought came to mind as to why they still use aluminum with ethanol. Just me thinking aloud and querying some thoughts.

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                        • #13
                          no problem just busting your chops

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                          • #14
                            Originally posted by 99yam40 View Post
                            no problem just busting your chops
                            Used to it..I'm married .. lol.. In addition, there are soo many bright minds on this forum that posing theoretical ideas to solicitate thoughts can be enlightening.

                            Comment


                            • #15
                              Originally posted by Nautical View Post
                              I was making a leap in referencing dissimilar metal corrosion as mentioned above with the thermostat housing. I have seen much corrosion inside aluminum VST and the thought came to mind as to why they still use aluminum with ethanol. Just me thinking aloud and querying some thoughts.
                              Heat transfer from the fuel or to the fuel by the aluminum is another thing they may have been thinking of when design was done.
                              But who knows for sure.
                              With all of the problems they have had with the filter cups, I am sure there would have been problems with a plastic VST also

                              Comment

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