Corrosion hole in exhaust elbow

[fxykty]

The temporary patch is set and working to prevent any leaking. I took the elbow off and nothing is visible inside - the soot coating looks solid. So the issue is other unseen corrosion that will make another hole.

I’ve got a local guy in Albany WA, where we’re stuck for a week waiting for decent weather to head west and north, who will make up two SS elbows to the same dimensions for less than the cost of a single OEM aluminium elbow. So I’ll keep these elbows as spares and should never have to worry about them again. I assume that the gasket provides enough separation of the SS and mild steel of the heat exchanger.

[Bluechart]

I agree, and I’ve replaced using HDI replacements, they supply gaskets too, great service!

[Shrew]

Originally Posted by fxykty

Attachment 273819

That anode looks almost TOO good. Also, I see what looks like the remnants of Teflon tape in the threads.

Are you wrapping the threads of the anode in Teflon tape? That would isolate the anode from the elbow and protect the anode. This would be the same as having no sacrificial anode and the elbow would then take the brunt of the galvanic corrosion.

[JBsurfin]

Originally Posted by fxykty

We have Nanni diesels in our cat, 35hp each. About 3 years ago we removed and serviced the heat exchangers and replaced the exhaust elbows as they had deep surface rust.

Just noticed that the port engine’s exhaust elbow has a hole, about 3mm diameter, that sprays salt water. I saw it after checking on why the engine bay bilge pump was coming on frequently.

Attachment 273820

Attachment 273821

The exhaust elbow anode is in very good condition, so I’m surprised that there is so much corrosion that it created a hole. The other side looks fine. Any ideas?



Attachment 273819

We’ve packed the hole with JB Weld, but haven’t tested it yet. I don’t think running the engine with that small hole is a big deal as it’s just raw water that isn’t going out the exhaust hose. We are ordering a new exhaust elbow.

Just a FYI. Hose down that engine to get that salt off it. Then spray it with a rust inhibitor. Also, most of these elbows are cast and are known to be porous, especially those made in China.

[Cynara]

Sometimes the hot exhaust gases will cause that

[fxykty]

Originally Posted by Shrew

That anode looks almost TOO good. Also, I see what looks like the remnants of Teflon tape in the threads.



Are you wrapping the threads of the anode in Teflon tape? That would isolate the anode from the elbow and protect the anode. This would be the same as having no sacrificial anode and the elbow would then take the brunt of the galvanic corrosion.

No, of course not.

[fxykty]

New mixer elbow installed. Will do the other side next.


Close up of the new elbow.


They have a tube within a tube - inner tube is for very hot exhaust gases and outer tube feeds the raw water.


The machinist cut open the old elbow. He was able to quadruple the size of the corroded hole just with a screwdriver - good thing I didn’t decide to just leave it!

[JPA Cate]

^^^^^

Indeed, a good thing. Well done, and spares, too.

Ann

[AKA-None]

Originally Posted by fxykty

New mixer elbow installed. Will do the other side next.
Attachment 274053

Close up of the new elbow.
Attachment 274054

They have a tube within a tube - inner tube is for very hot exhaust gases and outer tube feeds the raw water.
Attachment 274055

The machinist cut open the old elbow. He was able to quadruple the size of the corroded hole just with a screwdriver - good thing I didn’t decide to just leave it!
Attachment 274056

This is what I was alluding to a few posts back