I run my boat in salt water also. I now have six years on it and have the original exhaust manifolds and risers. I flush with fresh water on muffs at the house each time.
I would expect to get a couple more years out of my exhaust manifolds and risers.
(volvo 5.7L Gi DP)
I think the typical symptoms of exhausts and risers going are engine overheating --- typically the passsages corrode and restrict flow causing the engine to overheat. As flow is reduced in the risers the temperature of the risers also rises.
This can be detected with a heat gun. I have an inexpensive model that I just used this past weekend to start establishing a base line on my manifold temps. I just used it on the muffs, but want to use it when underway which should give me a better idea of the exhaust temps.
Yes -- internally leaking manifolds can lead to water in a cylinder and big issues. That is the main reason that some people replace manifolds and risers which are used in salt water after about 5-6 years just as preventative maintenance.
Living in Florida my boat is used year round. I intend to just monitor the condition through engine and exhaust temps. I did this successfully with my past boat which I had for over twenty years and went through exhaust manifolds and risers three or so times before I sold the boat.
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DaleG -- West Palm Beach FL
2003 240Horizon -- 5.7Gi -Duoprop
