Yanmar Exhaust Manifold Corrosion

[Jerry45]

My friend has a 2007 Catalina 387 with a Yanmar 3JH43, 40 HP engine and his exhaust manifold severely corroded at the six o'clock position immediately before the gasket between the manifold and exhaust elbow. The manifold started leaking and he replaced it. Now there is evidence of similar corrosion in the new manifold. We think salt water may be getting into the manifold, maybe through the exhaust elbow and collecting at the corrosion spot. However, we don't know how the water is getting in, if that is what is actually happening. We've check the anti-siphon valve in the raw water discharge hose upstream of the exhaust elbow and it seems to be working fine. Mechanics have been consulted but are unsure what is happening. One suggested modifying the exhaust elbow and raising it somewhat higher above the manifold but space limits the additional height to only a few inches. Another suggested a water lift but there does not seem to be room to install one. Another suggested electrolysis, and, believe it or not, the engine does not have zincs. At least not any that we can find on the engine itself or in the owners manual. The corrosion residue is a somewhat gritty, gummy substance that tastes salty. My friend has talked with Catalina and Yanmar but that was not helpful. We would appreciate any and all comments and suggestions about what is causing the corrosion and how to deal with it. We look forward to your responses. Thanks.

[GordMay]

Greetings and welcome aboard the CF, Jerry45.

[Chief Engineer]

Is it rust?

[Jerry45]

Chief,

The corrosion is inside the manifold and almost surely not rust. The corrosion residue is more granular, somewhat like salt.

Jerry

[DeepFrz]

I would suggest that it is time your friend gets in touch with Yanmar directly.

In the mean time perhaps some pictures of the installation and and some close up pictures of the corrosion might help in us being able to help your friend.

[Zanshin]

What you are seeing could be a mixture of scale buildup from the hot water mixed in with rust stains; that is what I had in my exhaust manifold when I replaced it.

[svcambria]

I believe you are correct about the lack of zincs in the engine - at least my 4JH3E doesn't have any.
Possible cause - an electrical ground attached to the engine manifold?

Michael

[delmarrey]

Jerry,

I would say that one of the flanges are not flat, allowing the salt water to leak while the motor is running, causing it to leak even more over time.


.

[Cheechako]

he can have a custom mixing elbow made that is higher and also longer.... so that the exhaust water dumps in the exhaust lower than it does now.

[iluvteak]

I have a 4jh2 and just discovered the exact same thing. Ditto on the 6 oclock position. But mine ate so much aluminum from that area that the fresh water water jacket is now exposed(about size of a quarter). Can't afford a new Exhaust mani/heat exchanger so I am having a welder look into patching her up.

We are suspecting the raw water is backing up and sitting there corroding away when engine is turned off. Mixing elbow looks clear though, not sure why salt water is backing up?? Ideas?

[delmarrey]

FYI - Can't weld cast aluminum, especially after exposed to saltwater. Cast aluminum is very porous and absorbs contamination.

[iluvteak]

FYI ... my experience says you can weld cast aluminum. I had the same exhaust mani/heat exchanger welded 7 years ago. Location was the perimeter of the heat exchanger area where the end cap is bolted on. The weld has held up great and saved me $$$!!! Maybe the welder was a magician ... someone in Ft Laud FL.

perhaps the mixing elbow location is a tougher spot due to heat?? Is this what you mean??

[delmarrey]

Originally Posted by iluvteak

FYI ... my experience says you can weld cast aluminum. I had the same exhaust mani/heat exchanger welded 7 years ago. Location was the perimeter of the heat exchanger area where the end cap is bolted on. The weld has held up great and saved me $$$!!! Maybe the welder was a magician ... someone in Ft Laud FL.

perhaps the mixing elbow location is a tougher spot due to heat?? Is this what you mean??

I had an long time expert try to weld up some winch bases and they sputtered and bubbled like they were plastic.

[delmarrey]

One more thing I might add. Most 3jh/4jh yannys have a bronze exhaust elbow, painted silver. That being next to an aluminum heat exchanger could be part of the problem.

There should be a gasket between the two but if that gets damaged then one might have an electrolysis problem with the aluminum being the anode.

[iluvteak]

Bronze painted silver. I guess that explains the $400 mixing elbow cost..thanks. I think you've nailed my issue of corrosion in the mani. The gasket was a corroded mess between the mani and elbow. So I guess the corrosion just went nutty and ate mani to pieces - right thru to the water jacket! Welder just told me it is beyond repair, full of holes from 3 oclock to 9 oclock on the mani. $875 new so I am in a pickle. Thanks yanmar nice design team ya got there ....