OT- Exhaust elbow on marine diesel

1996 Volvo Penta MD2030B, exhaust elbow clogged with corrosion (I presume due to saltwater/gas interplay) Any recommended chemical for this, or just chip away at it with "elbow grease" ?

muratic acid

A major turbocharger manufacturer has a manufacturing plant here as well as a turbo rebuilding facility. The guy who runs the rebuild op told me once when I was there looking at some stuff they were selling, that getting the burned on crud off the components was the single most difficult part of the entire rebuild process. At that time, about 4 yrs ago, they were baking the parts to further harden the crud, then brushing off anything that was loose, and finally blasting off the rest.

That said, I'm sure as a major corp they avoid using anything thats particularly wicked for health and safety reasons. There are soak type carburetor cleaning potions which employ a water seal over the working solution that will eat off most anything that's put in them. I don't know if they use methylene chloride or something similar, but they'll eat any sort of paint, fuel varnish, or most anything else that most solvents won't touch. A 5 gal bucket isnt cheap though, and its storage life is somewhat limited because its corrosive to a steel container and it'll eat a plastic one as fast as you can pour it in.

If there's anyone in the area who still uses a hot tank for engine component cleaning, the typical Oakite solution will probably take it off. Problem is, most automotive machine shops, etc have changed over to hot water type engine cleaners for environmental reasons, and its doubtful the cleaning solutions used in them would even phase the carbon deposits. If someone has a hot tank, it would definitely be the cheapest and easiest solution.

While I have not dealt with diesel manifolds or elbows I have dealt with a lot of Mercruisers. all used in salt water.
The problem is a combination of salt water and the heat/cool cycle.
The books recommend "Rodding" them out- digging with a rod to remove rust/scale. And/or having a radiator shop boil them.
I have seen too many that looked solid and as soon as I start digging they crumble and would have failed shortly if I had tried to used them.
I bought one boat with twin 140hp Mercruisers, the port engine had been run three weeks before I looked at it. When I looked at it it was locked up!! I bought the boat at a discount and had to rebuild that engine. I had to bust two pistons out of it.
It had a bad manifold. At low rpm they will suck water into the cylinders.

I once cleaned out a similar part with an O/A torch. I did it outside, since it made horrible smoke. I just got the carbon burning and turned up the O2. I had to stop periodically to let the part cool.

I would say blasting it out via pecan shell or dry ice.

sorry, but how much is a new one? and how much is "elbow grease"?

dian said:

sorry, but how much is a new one? and how much is "elbow grease"?

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With shipping and tax about $325

Milacron said:

With shipping and tax about $325

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That much ehh....
Barr Marine in Philadelphia used to make replacement maifolds and that overboard discharge part.
Wonder if they're still in biz

Milacron said:

With shipping and tax about $325

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I see Volvo marine parts prices in the US are as extortionat in the UK.

One problem with the elbow grease solution (at least on stainless bends, but I presume cast iron bends like yours are also prone) is that once you get rid of the grunge you may discover that the wall section is riddled with voids, where the gas first impinges against the far wall at the turn. Presumably the cooling water on the outside causes condensation on the inside during the early stages of warmup (sulphur > sulphuric acid) and it seems possible that carbon deposits which form at higher operating temps lead to galvanic (electrolytic) corrosion because of the potential difference between carbon and the base metal.

Things only get worse on raw water cooled engines when the first tiny voids form letting saltwater get at the back of the carbon deposit and electrolysis can really run rampant from this point, but even freshwater as in the MD2030B would not be helpful

Limy Sami said:

I see Volvo marine parts prices in the US are as extortionat in the UK.

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Yep, similar size elbow on a Yanmar is $125 (for direct comparison the base price of the Volvo one is $289.35 )

You can certainly try chipping the crud out, but at the end of the day the cast iron may well be getting thin and will eventually corrode through.

Exhaust elbows are considered a consumable item; relatively cheap to replace, but bad news if it blows on you while underway. A cabin full of exhaust gas won't make the missus happy!

How big is the elbow?, can you boil it in caustic soda and water to "hot tank" it like they do at the engine rebuilders, you'd have to be careful as at higher temps caustic soda will etch glass. It should only attack the corrosion and aluminium but not cast iron.

I have heard of a Gardner diesel that was losing power after years of use in a fishing boat. The exhaust ports in the head and the exhaust manifold were choked with carbon deposits as the engine was hardly ever run at rated power for any period of time. When the mechanic ran it flat out and got it to temp, lumps of hot carbon starting flying out the exhaust, it still needed a pull down and de-coking.