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Riser - life expectancy in the North East. FWC Merc 350 Mag 5.7l

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Riser - life expectancy in the North East. FWC Merc 350 Mag 5.7l

Old 04-08-2015, 06:06 AM
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Default Riser - life expectancy in the North East. FWC Merc 350 Mag 5.7l

I was curious if there is any change to the serviceable life expectancy of risers on a FWC engine in the North East opposed to other areas in the country. 5-7 years of service seems to be the norm with inspections and gasket replacements every 2-3 season.

  • Water temperature is colder, about 60-65 deg average surface temp.
  • Boat lives in salt water for 4-5 months a year.
  • After pulling it is flushed with fresh water and eventually winterized with marine antifreeze and left untouched for 6+ months.
  • Dry joint exhaust/ risers (not sure if it makes a difference)

I purchased this boat last year and know the previous owner and the history. Engines were new in 2009 and the boat did not make it to the water in 2011. So the risers have really only been used for 4 seasons. Engines have less than 200 hours. Merc 350 MAG MPI's 5.7l. I have had a boat on the same dock since 2004 and am 100% confident in the accuracy of the statements above.


The engines run great and oil did not appear to have any salt water intrusion end of last season.


During inspection I was thinking of coating the inside of the manifold in Corrosion X, Can't hurt right? Anyone else hear of or do anything like this to possibly hold off a little more corrosion???


Thank you for any advice. I really appreciate it.
Old 04-08-2015, 07:02 AM
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fwc merc style 6-8 yrs. crusader style 8-10 for manifolds. risers 3-5 along with elbows. you can spray the outside but wont help with longevity. routinley flushing with fresh helps extend life.
Old 04-08-2015, 07:28 AM
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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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