Old 04-08-2015, 07:28 AM
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Join Date: Nov 2002
Location: Long Island, NY
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With the Merc dry joint system you have one advantage in that the exhaust gas passage is separated from the cooling passages much more so than on the standard wet joint designs. This means that you're less likely to have erosion of the cast iron sealing surfaces and leaks, but that's more common with raw water cooling anyway. However, dry joint or not, if a riser rusts through, you can still get salt water in a cylinder. The problem is that we as backyard mechanics can never really know how much cast iron is actually left and how close you are to rusting through. So its best to think of risers in salt water as a maintenance item like anodes on an outdrive. 5 years is a good guide, if you replace them then, chances are you will never had a salt water in the engine problem. Here is what an OMC one piece manifold outlet looked like after 5.5 seasons here in the Long Island Sound region looked like. Similar use to yours, moored in salt water, not flushed till the end of the season, filled with the best -100 marine antifreeze each winter. These could be rodded out and used again, but you really don't know how much iron is left....
The last pic was what it looks like after cleaning it out. Not sure if I'd use it again or not.
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