Yanmar Exhaust Manifold / Heat Exchanger Corrosion

[iluvteak]

Ideas on what could cause such extensive corrosion on my exhaust manifold ? Its gotta be sea water to be this bad I think ? As you can see in the pic the corrosion is from 3 oclock to 9 oclock position where the mixing elbow attaches. I've seen a few threads on this and posted but thought I'd get a pic up to see what everyone thinks.

I have tested the mixing elbow and it does not seem to be leaking raw water into the exhaust tube/trap so I am really baffled ? Raw water is flowing fine at the back of the boat (wet exhaust). Could the muffler be causing a backup into the exhaust manifold ? If so how would I test this ?

Thanks in advance, great forum for ideas.

[delmarrey]

Are your manifolds aluminum, and your exchanger core bronze? If so, that is the problem. Yanmar didn't think when they built their systems. When mine goes, I'm retrofitting with an aftermarket unit.

You have to keep them leak free or they start using the aluminum as an anode, which reminds me, I need to install zincs in mine. The factory doesn't.

[sailorboy1]

Alum manifolds, were they really that stupid? Got to take a magnet to the boat this weekend.

[Noname]

I have been told there are no zincs on the yanmar that is freshwater cooled. I have the 3GM30F, looked crazily to find the zincs to replace only to discover later that the zincs were only put in the raw-water cooled engines. My engine is a 1985 model and still has the original manifold (not the exhaust riser). I would also appreciate experienced, informed input as well regarding the subject.

[delmarrey]

BTW the mixing elbow on the 3JH & 4JH are bronze also. A gasket is the only thing keeping them apart.

[delmarrey]

Originally Posted by Seaduction

I have been told there are no zincs on the yanmar that is freshwater cooled. I have the 3GM30F, looked crazily to find the zincs to replace only to discover later that the zincs were only put in the raw-water cooled engines. My engine is a 1985 model and still has the original manifold (not the exhaust riser). I would also appreciate experienced, informed input as well regarding the subject.

I plan to make custom zincs, but haven't figured where to install them yet. There are a couple plug holes that I'll be checking out.

[DeepFrz]

That exhaust port looks like it was chewed out by rats. I guess Yanmar was one of the Japanese companies that missed the "Quality" training.

[delmarrey]

Here's another thread related to the exhaust problem.

http://www.cruisersforum.com/forums/...ion-69909.html

[Noname]

Does anyone think that nonconductive gasketing and washers would be of any help?
KSC Corrosion Technology Laboratory -- Galvanic Corrosion

[iluvteak]

Originally Posted by delmarrey

BTW the mixing elbow on the 3JH & 4JH are bronze also. A gasket is the only thing keeping them apart.

As luck would have it, a guy in the marina has the same engine. he had a leak near the elbow too an he pulled the elbow off today. His gasket is shot too, but no corrosion in the manifold? Note his elbow is steel, tho, not the silver painted bronze that I seem to have.

I still think sea water is backing up and sitting in the manifold tho. But how is the question? I just cant see corrosion doing that kind of damage....

[Tellie]

My vote is galvanic corrosion not sea water. If it were sea water you would most likely have most of the damage where the sea water would sit on the bottom of the flange area as the motor sat idle and unused. Also it would be throughout the exhaust. You have fairly even corrosion 360 degrees right at the flange and it appears from the pic no further in. If sea water were the culprit you would have had sea water throughout the exhaust manifold and it would have surely hydrolocked that engine long ago.

[delmarrey]

Steel and aluminum are a lot closer on the electropotential series. I'll bet he still has some erosion though. Also my guess is that starting and stopping a lot would speed up the process, allowing for fresh saltwater to be introduced often. But just a guess.

Galvanic series - Wikipedia, the free encyclopedia

[DeepFrz]

If people are experiencing "leaks" then water must be getting up there somehow. Perhaps it is condensation, but if you see wet leaking down it is some kind of water. Obviously not enough to hydro lock the engine but enough to rot out the gasket and corrode out the aluminum that is right next to the bronze.

[Tellie]

Like he said 3 oclock and 9 oclock. That means the manifold would have to be half full of water while not running and a for certain hydrolock on the next start up.

[DeepFrz]

Looking at the picture it looks like most of the damage is at 6 o'clock. But it looks like it just might be a crappy casting that has been eaten out by the acids in the exhaust.

But we are all just guessing. iluvteak, why not contact Yanmar directly and ask them to take a look at it.