exhaust system failure on I/Os and IB's cause a lot of problems(especially in salt). If left alone and not fushed with fresh water after each use, raw water manifolds last about 3 seasons before they need repalcement in our area, usually if you wait to the fourth season, you have waited too long and you now have damage to the engine. If they are flushed with fresh water after each use, I've seen them last five to seven years. fresh water cooled(antifreeze) manifolds generally last much longer, with the risers giving up somewhere between 5 to 10 years. You have to watch it no when ordering fresh water cooling on new engines as most of them do not include the manifolds as part of the fresh water system.
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