Corrosion hole in exhaust elbow

[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.





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?



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.

[Tin Tin]

Were the replacements OEM?


Some thoughts:
Do you fresh flush your engines and leave fresh water in the system - if so depending on time frames etc the zinc anode in fresh water may form a boundary layer that will then not work in salt water effectively and so they should be abraded before going back to salt. Aluminum anodes may be better.


Third thought, it seems to me marinized tractor or truck engines that I have owned require anode protection in the raw water system, many Yanmars are designed from ground up as a marine engines and do not require anodes, may be that is why my 4JH5E heat exchangers and elbows went for 8 years full time cruising and then I only replaced the elbows out of caution, but they looked fine to me.

[fxykty]

Originally Posted by Tin Tin

Were the replacements OEM?


Some thoughts:
Do you fresh flush your engines and leave fresh water in the system - if so depending on time frames etc the zinc anode in fresh water may form a boundary layer that will then not work in salt water effectively and so they should be abraded before going back to salt. Aluminum anodes may be better.


Third thought, it seems to me marinized tractor or truck engines that I have owned require anode protection in the raw water system, many Yanmars are designed from ground up as a marine engines and do not require anodes, may be that is why my 4JH5E heat exchangers and elbows went for 8 years full time cruising and then I only replaced the elbows out of caution, but they looked fine to me.

Yes, the replacements are OEM.

No, we do not bother to flush with fresh water as we are using the engines frequently (generally not more than a fortnight of non use).

The JB Weld held during 10 minutes of motoring into an anchorage and setting the anchor. In our next longer stop I will remove the elbow and inspect from inside.

[Searles]

Those exhaust elbows are alloy of some type ,use as a pattern and get new ones made out of black iron ,not SS ,but still fit with anodes will out last the engines .⚓️⛵️

[hpeer]

I find HDI replacements much better and much cheaper than OEM. My OEM Yanmar exhaust elbow was junk and had to be welded several times due poor fabrication.

https://hdimarine.net/product/gm-sta...-mixing-elbow/

[SailingHarmonie]

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.

Be careful about this. Running the engine with this leak COULD have issues. These are generic comments that might not apply to your exact physical arrangement, which I do not know.

The obvious is salt water spaying around. That will cause damage to many things very quickly.

If the water coming out is a significant fraction of your total cooling flow, and has not mixed with the exhaust gases yet, you risk overheating the exhaust system down stream.

There is gas blowing out with the water. That gas is diesel exhaust. You REALLY do not want that inside your boat.

If these have corroded through on the outside, there is a significant risk they are severely compromised on the inside. This can lead to short-circuiting of the normal path, and risk getting water back into the engine.

The mixing elbow is a weak point in the design of any wet exhaust engine. When they fail, multiple bad things can happen, above and beyond leaking water.

[sailingunity]

I don't have the same engine as you, but I've had pretty good luck with a 316 SS exhaust elbow we had made by a machine shop. It's simple, but has withstood corrosion much better than the original. Because we went to a non-marine place to have it made, it was reasonably priced!

[Scrimshaw4]

I replaced my elbow at 1000 hrs with a SS from HDI. It's rated at 2000 hrs. Your call. JMHO

[skipperpete]

Are the OEM Nanni mixer elbows stainless steel or aluminium castings, from your pics it’s hard to ascertain.

[fxykty]

Originally Posted by skipperpete

Are the OEM Nanni mixer elbows stainless steel or aluminium castings, from your pics it’s hard to ascertain.

Aluminium

[fxykty]

Originally Posted by SailingHarmonie

Be careful about this. Running the engine with this leak COULD have issues. These are generic comments that might not apply to your exact physical arrangement, which I do not know.



The obvious is salt water spaying around. That will cause damage to many things very quickly.



If the water coming out is a significant fraction of your total cooling flow, and has not mixed with the exhaust gases yet, you risk overheating the exhaust system down stream.



There is gas blowing out with the water. That gas is diesel exhaust. You REALLY do not want that inside your boat.



If these have corroded through on the outside, there is a significant risk they are severely compromised on the inside. This can lead to short-circuiting of the normal path, and risk getting water back into the engine.



The mixing elbow is a weak point in the design of any wet exhaust engine. When they fail, multiple bad things can happen, above and beyond leaking water.

Thanks for your comments and the generic cautions - all good things to keep in mind.

Salt water spray isn’t great, but it’s not like that doesn’t happen with splashing and whatever. At least it’s at the aft end of the engine and not forward where all the electrics are.

Our engines are in their own compartments aft of the living spaces and with watertight bulkheads. There is no chance of exhaust gas into the cabins.

The volume of water leaking (not anymore after the patch job) is small - much less than what is going out the exhaust - so I don’t think overheating the exhaust is happening.

I absolutely will remove both exhaust elbows and check their insides. Getting new gaskets is going to be the biggest pain.

[Mickeyrouse]

A competent welder familiar with aluminum should be able to repair that pin hole. But if there’s one you see, it’s likely more are about to erupt. I’d repair it, but keep it as a stand-by and get a new one. One never know, do one?

[AKA-None]

Originally Posted by Mickeyrouse

A competent welder familiar with aluminum should be able to repair that pin hole. But if there’s one you see, it’s likely more are about to erupt. I’d repair it, but keep it as a stand-by and get a new one. One never know, do one?

Yes and one thing to consider is that pinhole could be masking a thinner area that is not readily visible

So welding could simply open up a much larger area

[Ballsnall]

Originally Posted by fxykty

Aluminium

This is a cast product so it was probably just a casting defect and not from corrosion.
A weld repair would be simple to do and effective to get full life from the elbow.

[1affiah]

It could be a defect in the casting, I would drill out the hole and insert a screw.
I always carried automotive fiberglass "header tape" as patch material, along with tin can sheet metal and hose clamps for patches as well.