Yanmar 4JH3E exhaust corrosion.

[nonam]

I took the water injection manifold off a 4JH3E to see its condition.It was ten years old.The part looks to be in fine condition without carbon buildup.But what I found was corrosion on the engine side of the exhaust gasket.Right next to the exhaust gasket the alloy was pitted and eaten away right around the circumference of the exhaust.Am I right in thinking that there is nothing to be done to remedy or prevent this?At the present rate of corrosion the part might last another ten years and will need to be replaced when there is a danger of the exhaust leaking?

[nonam]

I just took the end cover off the heat exchanger which was leaking.Some of the metal there is rotten.It looks like we are up for a whole new exhaust manifold.I wonder what that is going to cost.I looked up the book that came with this engine to see what it says about zincs.It doesnt say anything.

[sailabroad]

Did you find the cause? Did you get any Information from yanmar? I am also seeing this corrosion.

Thanks.

[a64pilot]

You may not have engine zincs, I don't on my 4-JHE
I don't think though that you should have corrosion upstream of the elbow, water shouldn't ever get there? You sure the elbow doesn't have an internal leak?

I'd call Mack Boring or someone else, I wouldn't try to go to Yanmar

That is a picture of the exhaust manifold, where the elbow bolts onto right?

[sailabroad]

I have seen some evidence of water at lowest exhaust port.

No pinholes in elbow, mains water pressure tested between fresh, raw and exhaust manifold sides for leaks all OK.

Apparently no zincs as raw water side of exchanger is all Bronz - its a beauty when pulled apart!

A mechanic told me Beneteau blame yanmar and yanmar blame beneteau installation.

The installation meets yanmar specs, just.exhaust pipe run is very long and swan neck is just close enough to engine..wet exhaust rise to engine is marginal but just in spec..

The mechanic also told me it's caused by seawater forced into exhaust manifold from a big following sea/waves.

I raised my swan neck hoping to fix the issue.. But checked yesterday and I have more corrosion than last time I checked..

I now have a pipe + manual bildge pump from the vetus wet exhaust on the drain plug to the bildge to drain wet exhaust when sea is rough .

An aussy mate just got his successfully welded up.

Emailed yanmar but not expecting a reply - i will try macs.

It looks(to me) like acid from the sulphur? In the exhaust gasses and sea water mixing corroded the aluminum?

[sailabroad]

Yanmar replied to my email with the suggestion that the corrosion is caused by electrolysis through bad wiring/installation in our boat, don't know how that would be possible without any water, as the exhaust is dry. I'm asking for further information.

[a64pilot]

Might want to look into a thru hull with a rubber flapper on it if your getting water back into your exhaust?

[transmitterdan]

I have same engine with 2K hours. No corrosion at this joint. I think it is an installation problem. There should never be water at this joint. It should just be hot exhaust gasses at that point. The water should be injected downstream from this flange. If salt water is hanging around this flange then that's a big problem.

[MooGroc]

I have the same engine (well, a 3JH3E) with well over 2k hours and had the exhaust apart just the other day and have no corrosion. I would think if you were getting salt water there on a regular basis, you'd have bigger problems by now.

I'd suggest looking into the electrolysis cause. Not sure how you troubleshoot that....

Good luck.

[transmitterdan]

Originally Posted by MooGroc

I have the same engine (well, a 3JH3E) with well over 2k hours and had the exhaust apart just the other day and have no corrosion. I would think if you were getting salt water there on a regular basis, you'd have bigger problems by now.

I'd suggest looking into the electrolysis cause. Not sure how you troubleshoot that....

Good luck.

Even electrolysis requires some kind of electrolyte to transport the ions. If that area ever gets wet that's a bad thing IMO. It's a short path from there to the exhaust valves and then into the cylinder bores.

[redsky49]

Originally Posted by nonam

I just took the end cover off the heat exchanger which was leaking.Some of the metal there is rotten.It looks like we are up for a whole new exhaust manifold.I wonder what that is going to cost.I looked up the book that came with this engine to see what it says about zincs.It doesnt say anything.

What is the white material on the inside? Is it salt?

[kmacdonald]

Originally Posted by transmitterdan

I have same engine with 2K hours. No corrosion at this joint. I think it is an installation problem. There should never be water at this joint. It should just be hot exhaust gasses at that point. The water should be injected downstream from this flange. If salt water is hanging around this flange then that's a big problem.

I agree.

[sailabroad]

Did the Original poster find the cause? I found a bit more information

I now believe it is a Galvanic problem - my exhaust manifold is still slowly rotting. A Yanmar mechanic told me it is a galvanic reaction but not why.

I have verified that somehow seawater, vapour? gets up the exhaust elbow as far as the exhaust gasket, but probally the exhaust manifold - There is NO leak in my exhaust elbow - and it is NOT blocked

How is seawater/vapor? moving against the air pressure from the exhaust gases? perhaps? but still how? when the engine is shut down.

When water is in the exhaust manifold a galvanic reaction can occur between the stainless gasket and the cast aluminum

Perhaps a non ferric gasket might help? also it looks like the exhaust elbow studs are isolated by some white cement?

[geoleo]

Originally Posted by redsky49

What is the white material on the inside? Is it salt?

NO zincs on 4JH3 Yanmar Factory said not needed

[sailabroad]

I think a zinc would have to be close, in the exhaust water and electrical bonded to the exhaust manifold. Yes my engine like your has no raw water zincs..

Hmm...need to think about it a bit.