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Heat Exchanger?

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  • Heat Exchanger?

    Ok so I thought I had my overheat heating issue figured out but apparently not... much to my dismay. When I bought the 17' er I was told it had an overheating issue. I'm working with Mitsubishi 4140 with a split system. I topped off the heat exchanger with antifreeze and ran it on the hose and it boiled over in about 5 minutes. Once it cooled down I opened the cap and all the antifreeze was now raw water. So I pulled the heat exchanger and capped the inter system on one end and put it under a small amount of air pressure and it was leaking down. To me something cracked inside... maybe it wasn't winterize properly. I had a new heat exchanger made and ran it, 150° for 30 minutes on the hose. It looked promising. Took it out for a shake down cruise today and after about 20 minutes she claimed to 200° and started boiling out the heat exchanger cap. Did a quick peek in the heat exchanger and it appears to have raw water in it again. What an I missing?
    Last edited by Striper Sniper; 11-09-2021, 08:50 PM.

  • #2
    Check the riser gasket if it's a full fwc. That's the only cross over location I can think of. The trans cooler would leak into the tranny.
    Atlantic City, NJ
    1982 Cuddy, Rebuilt 351 .060 rings, Edelbrock carb

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    • #3
      I have had problems with my riser gaskets before. The exhaust manifold on a full FWC system is full of coolant. The Riser is raw water.

      Make sure you dont have any hoses crossed.
      '78 20ft Cuddy
      Mercruiser 350 FWC preVortec w/Carb

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      • #4
        Originally posted by Pedlyr View Post
        I have had problems with my riser gaskets before. The exhaust manifold on a full FWC system is full of coolant. The Riser is raw water.

        Make sure you dont have any hoses crossed.
        Humm hoses crossed, is that even possible, I guess anything is. I'll check it when I'm back home in a few days.
        thanks
        Pat

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        • Pedlyr
          Pedlyr commented
          Editing a comment
          Ive done it before on my V8. Not sure how your hoses are set up

      • #5
        So just so I'm not misunderstanding the two functions of the heat exchanger let me summarize my understanding. The outer part that holds the antifreeze circulates through the block and cools the engine, the inter part is raw water and cools the exhaust.... correct?
        Thanks
        Pat

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        • #6
          That's partially correct. In a partial fresh water cooled (fwc) system the raw water goes through the heat exchanger and the exhaust manifolds and then through the risers cooling the exhaust gases. The raw water cools the antifreeze in the second loop in the heat exchanger (he). In a full system, the antifreeze flows through the block and exhaust manifold but not the riser. The raw water enters the riser through a fitting and exits through the the spiral fluted in the exhaust portion of the riser cooling the exhaust gases. There is a block off plate and gaskets separating the riser and manifold. The gaskets leak and the block off plate corrodes allowing the raw water to mix with the coolent. On a partial system, the block off plate is not installed because the manifold has raw water in it too.
          Atlantic City, NJ
          1982 Cuddy, Rebuilt 351 .060 rings, Edelbrock carb

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          • #7
            I think it has to be in the HE.
            1988 26' cuddy
            1975 20' open
            16' Sandpiper
            14' Certified Fiberglass

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            • #8
              Originally posted by Quik Fix View Post
              I think it has to be in the HE.
              Jerry the H.E. is brand new, I had it made. I'll need to dig a little deeper into the cooling system.

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              • #9
                Originally posted by Ship View Post
                That's partially correct. In a partial fresh water cooled (fwc) system the raw water goes through the heat exchanger and the exhaust manifolds and then through the risers cooling the exhaust gases. The raw water cools the antifreeze in the second loop in the heat exchanger (he). In a full system, the antifreeze flows through the block and exhaust manifold but not the riser. The raw water enters the riser through a fitting and exits through the the spiral fluted in the exhaust portion of the riser cooling the exhaust gases. There is a block off plate and gaskets separating the riser and manifold. The gaskets leak and the block off plate corrodes allowing the raw water to mix with the coolent. On a partial system, the block off plate is not installed because the manifold has raw water in it too.
                Okay I need to process this info and do a little exploring.

                If my exhaust manifold is clogged would that cause the antifreeze to overheat and boil out the cap?

                Pat

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                • #10
                  Again only if a partial fwc system. And not because of routing but a clogged exhaust will cause back pressure in the combustion chamber. Which system is yours? There is a manual in the collection for the Mitsubishi engine.
                  Atlantic City, NJ
                  1982 Cuddy, Rebuilt 351 .060 rings, Edelbrock carb

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                  • #11
                    Simple answer, yes. BUT it wouldn't get raw water in the expansion tank.

                    If my exhaust manifold is clogged would that cause the antifreeze to overheat and boil out the cap?

                    Pat [/QUOTE]

                    1988 26' cuddy
                    1975 20' open
                    16' Sandpiper
                    14' Certified Fiberglass

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