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post #1 of 2 Old 06-07-2013 Thread Starter
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Exhaust Header- Direct Sea Water Cooled

My 33 year Yanmar 3GMD is direct sea water cooled. Thus the exhaust header sees both heat and salt water. Combination that will lead to corrosion of the cast iron part. If the salt water cooling passage corrodes through, salt water can hit the valves and could enter cylinder.

Has anyone replaced this part as a part of routine maintenance? If so, how often? A failure of this part could doom the engine. Seeing we routinely replace the mixing elbow that is bolted to the exhaust header, seems it would require routine maintenace also, at least for ancient engines.

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post #2 of 2 Old 06-08-2013
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Re: Exhaust Header- Direct Sea Water Cooled

My first 2GM-20 was about 10 years old when I bought the boat. I ran it for another 5 years exclusively in salt water and never had a problem.

My current 2GM-20 had less than 10 hours on it when I got my current boat. The engine had long been out of production, but the guy who restored the boat had this engine in its crate for about 5 years.

Since owning this boat these past three years, I have put about 1000 hours on the engine (no hourmeter but estimate based on 250 days sailing at 4 hours a day motoring) and so far, so good. When I mentioned corrosion in salt water cooled engines to the local Yanmar dealer he said not to worry until about the 15 year point.

I would expect a rotten header to give some warning indications, like weeping a bit around the studs and gaskets.

Some people suggest fitting a freshwater flushing adapter, which could prolong the life of some items like mixing elbows and exhausts, if you can be bothered connecting up a hose every time you return to the dock. Much of the sailing I do does not involve very frequent returns to the dock, so I have not yet bothered with this, though am thinking about it for the next winter lay-up. The boat stays in the water through the off-season.

Last edited by arvicola-amphibius; 06-08-2013 at 02:44 AM.
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