Exhaust Elbow - corrosion

[KevinT1]

Have removed the Exhaust Elbow from our 1998 MD22 to check and clean - this is the 1st time I've done this in the 6 years of ownership :ambivalence:

Having cleaned / scraped out the deposits ( the water entry pipe was almost blocked ) - I can see 2 holes in the Main Pipe through to what I would call the water jacket - one at the top looks to be the water entry and looks solid, but there is another hole opposite on the bottom wall looks as though it has been caused by corrosion

questions -
1) what is the purpose of the water jacket - to heat up the incoming water ?
2) should there be just the top hole ( I can imagine that this would spray the water down into the exhaust gases ) , and thus what would the effect be of using the engine with the lower hole "leaking water"

The external walls are all solid - so there is no chance of exhaust leaks into the boat

Unfortunately "parts4engines" have their replacement elbows on back order due sometime around the end of April otherwise I would be replacing it.

thx, Kevin

 

[RichardS]

The purpose of the water jacket is simply to cool the exhaust gases and the elbow itself before the point where the water is actually injected into the exhaust. My elbow has a sort of inner sleeve so it's like a 360 degree hole, rather than a specific hole, where the water mixes with the gas but I don't know your elbow so maybe yours has 1 mixing holes or maybe it has 2.

Do you have a diagram or can you ask the supplier?

Richard

 

[Heckler]

Have removed the Exhaust Elbow from our 1998 MD22 to check and clean - this is the 1st time I've done this in the 6 years of ownership :ambivalence:

Having cleaned / scraped out the deposits ( the water entry pipe was almost blocked ) - I can see 2 holes in the Main Pipe through to what I would call the water jacket - one at the top looks to be the water entry and looks solid, but there is another hole opposite on the bottom wall looks as though it has been caused by corrosion

questions -
1) what is the purpose of the water jacket - to heat up the incoming water ?
2) should there be just the top hole ( I can imagine that this would spray the water down into the exhaust gases ) , and thus what would the effect be of using the engine with the lower hole "leaking water"

The external walls are all solid - so there is no chance of exhaust leaks into the boat

Unfortunately "parts4engines" have their replacement elbows on back order due sometime around the end of April otherwise I would be replacing it.

thx, Kevin
View attachment 69659

There are two holes opposite each other where the water is injected in to the exhaust stream. When the MD22 goes bad the outside skin corrodes through on the left hand side, you start to see a rusty weep as the wall gets thinner.

 

[Shearmyste]

We had our inner jacket fail on a Perkins, the engine and exhaust system was poorly designed (outlet of exhaust and ejection point for the cooling water was below the water line), we also had a concurrent failure of the anti siphon line (blocked with salt), the result was the finding of what looked like mayonnaise for oil, guess what the sea water siphoned back through the engine, lucky the engine was salvageable. There is a great article on design of water injected exhausts which gives all the info needed, bit american but it is good to read. https://www.sbmar.com/articles/designing-a-marine-exhaust-system

 

[KevinT1]

There are two holes opposite each other where the water is injected in to the exhaust stream. When the MD22 goes bad the outside skin corrodes through on the left hand side, you start to see a rusty weep as the wall gets thinner.

Thanks Stu, sounds like as I have 2 holes and the outer jacket is solid, then I’m ok to put it back on and stop worrying !

 

[sailaboutvic]

Thanks Stu, sounds like as I have 2 holes and the outer jacket is solid, then I’m ok to put it back on and stop worrying !

has Stu said two holes we take our out every year and give it a clean , worth doing