Volvo exhaust muffler

[Symphony]

Another victim. Corrosion at the outboard spigot weld. Jet of warm salty water filling the bilge sump behind the saildrive. Not obvious until I went out in some bouncy weather two weeks ago and the water sloshed over into the under engine area and then across to the compartment under the galley.

Big difference from other failures is that the engine has only done 160 hours in 3 years. Fortunately the Volvo system seems to have my engine listed as having a 5 year warranty so my local dealer, Golden Arrow is replacing the muffler under warranty. Only downside is that it will be another Volvo one, whereas if I was paying myself I would replace it with a Vetus.

[tiger79]

Sorry to hear that, but it may just be a random weld failure.  The Volvo muffler on my old Hallberg-Rassy was 24 years old and still watertight when I sold the boat.

[Harry Brown]

Mine has gone also. (see pics)
Looks like the actual material has failed.
12 years old.
I bought this one from Force 4.
https://www.force4.co.uk/force-4-waterlock-silencer.html?sqr=waterlock&
Haven't fitted it yet, will do in the next couple of weeks.

[Salty]

I replaced my old and leaking Volvo silencer with the cheapest plastic one advertised in the Force4 catalogue, cost at the time about £56 and that was a two or three years ago. The connections on the new silencer were stepped so it would accept a range of different size exhaust hose. Being plastic it won’t rot like the stainless ends on the Volvo silencers are inclined to do, and neither would it leak carbon monoxide into the cabin area due to such rot, but I was concerned at the time about exhaust gas temperatures and whether they might cause the plastic to melt and so I fitted a temperature monitor to the exhaust hose on the upstream side. Up to now I’ve not seen temperatures above 32 degrees Celsius so my fears were unfounded, and in any case the exhaust hose would melt as well. The cheapo silencer has worked very well so far, and there is little or no discernible difference in engine exhaust noise. Time of course will tell whether cheap plastic will last or not, but if all the doom and gloom about how long plastic can hang around when left out in the ocean, then I see no reason why it should not outlast its Volvo predecessor. As for buying a plastic Vetus silencer, nothing against them except in doing so I’d be paying extra for a brand name with no good evidence that it would last longer, after all the Volvo silencer didn’t do too well did it?

[Craig]

The reality is that the "wet Exhaust" system contains hot, salty, stagnant water laced with NOX and SO2 from engine exhaust. ( read Nitric and sulphuric acids)  Even the stainless steel used in the Volvo exhaust is no match for this combination. Corrosion appears more linked to time than usage.

Any of the all Plastic systems seem to last much better than the Volvo exhaust and cost a fraction of the price.

Craig
" Shirley Valentine"
Gold Coast
Australia

[Salty]

The corrosion is caused by oxygen depletion within the stagnant water that remains inside the exhaust silencer between successive engine runs. The only reason why stainless steel remains “stainless” is because it requires oxygen to enable it to build up the right kind of surface. Take away the oxygen by leaving that water stagnant and you have the right conditions for corrosion to occur. Arguably the best way to prevent such corrosion would be either to keep a flow of oxygenated sea water through the exhaust system at all times, or to drain all of the water out of the exhaust system where stainless steel components exist whenever the engine is not running, after all stainless water injection bends don’t corrode in the same way do they???
Alternatively remove Volvo’s sometimes bright shiny and definitely very expensive stainless steel silencer and as Craig says fit plastic at a fraction of the price !!
Just one thing though Symphony, will your new silencer get a new 5 year warranty period with it, because if so, then you are onto a winner when it corrodes through again in three years time !!

[JEN-et-ROSS]

but I was concerned at the time about exhaust gas temperatures and whether they might cause the plastic to melt and so I fitted a temperature monitor to the exhaust hose on the upstream side. Up to now I’ve not seen temperatures above 32 degrees Celsius so my fears were unfounded, and in any case the exhaust hose would melt as well.

Still a valid concern Salty...
  My brother's yacht had a Vetus muffler (as does ours). In his case a sudden blockage of the water injector in the exhaust elbow caused, as you can imagine, a sudden and rapid increase in exhaust gas temperature entering the muffler. This caused instant 'melting' of the said plastic muffler, resulting in the clouds of noxious exhaust fumes pouring out of the companionway accompanied by a sudden deafening engine roar as the first sign of a problem.
  The muffler was unrecognisable upon removal, looked like blancmange gone wrong....
He replaced it with another Vetus one, I believe it will still be giving excellent service today........Bill

[Symphony]

Salty is correct. Stainless is susceptible to crevice corrosion - little to do with anything in the exhaust gases. The corrosion does not generally occur on the flat end plates or the spigot tubes but starts at the welds. If there is any occlusion in the weld then it potentially forms a pocket or crevice where there is a potential difference between the metal at the top and bottom of the crevice. Add in stagnant salt water and you have an electrolyte to start the action.

From what I have seen so far the failure is a pin hole in the weld at the bottom of the outlet spigot - a perfect location for the conditions as described. Problem is that it is difficult to spot poor welding visually. In another life I was involved with a product with a similar problem. All the welding on literally thousands of units over the years was done by the same person but a tiny percentage suffered from crevice corrosion despite there being no visible difference in the welds.

If anybody wants to read further on the subject then I suggest  Metals in Boats by Vyv Cox, available as ebook. Vyv is a real expert on the subject writing regularly in PBO and YM.

As to the warranty, doubt there will be 5 years on the replacement. I now recall that at the end of 2 years I had a dealer service (very expensive!) for an extended warranty, which seems to have paid off as I guess the cost of the replacement muffler plus fitting will be well over £500. Fortunately the dealer is having to replace the MDI as I posted earlier so will do both at the same time, hopefully next week.

If the replacement does fail in the same way in a short period I would use the Consumer Rights Act provisions as it would be possible to show that the defect was there from the start, particularly if the claim is supported by a technical report from somebody like Vyv.

[artemis]

Funny this subject has come up II just put the boat in the water a couple of weeks back all ok, Started the engine no motored to my berth, Let the engine run a whilst to see all ok, Opened up the step's to check all ok seen a small amount water, ok had a look see where the water was coming from could not see a thing. Tasted it salt water into the rear cabin remove the cushions and remove the boards, still could not see a thing. took a piece of dry paper towel and started took me ages to find it was a pin hole on the outlet side of the muffler, removed it took it to a welding shop who do stainless welding and its good as new now they did a great job.

Mike
Artemis

[dawntreader]

Funny this subject has come up II just put the boat in the water a couple of weeks back all ok, Started the engine no motored to my berth, Let the engine run a whilst to see all ok, Opened up the step's to check all ok seen a small amount water, ok had a look see where the water was coming from could not see a thing. Tasted it salt water into the rear cabin remove the cushions and remove the boards, still could not see a thing. took a piece of dry paper towel and started took me ages to find it was a pin hole on the outlet side of the muffler, removed it took it to a welding shop who do stainless welding and its good as new now they did a great job.

Mike
Artemis

Mike, I did the same. Lasted about 2 years then completely failed. Recommend you buy plastic now and avoid the obvious  . No noticeable increase in noise, no rusty water and peace of mind 

[Graysailing]

I Just Notice that mine has started to weep again, Managed to get a second hand one in good on Condition off of Ebay and will get the Old one Repaired
They only seem to last 5-7 year


Last Chance 38
Medway

[Craig]

Sorry Guys,

My previous post was misleading.

I was referring to problems with exhaust systems, not just the "wet Muffler".

The exhaust gases contain hot, salty water, some sulphur and NOx from the combustion process.

The acids formed  are not very friendly to the exhaust elbow" whereas the stagnant salty water attacks the wet exhaust.

I agree with the above comments that replacing the Volvo wet exhaust with a plastic system is a no brainer.

I also think that it is a no brainer to replace the exhaust elbow with a stainless steel system.

The stainless steel exhaust elbows are about 1/2 the price of the inferior Volvo elbow and the Vetus plastic exhaust much cheaper and better than the genuine Volvo wet exhaust.

Craig
" Shirley Valentine"
Gold Coast
Australia

[Symphony]

That is the problem with stainless steel. In its sheet or tube form it is very corrosion resistant. The problems start when it is welded (or in contact in sea water with other metals when electrolysis may occur).

So in the exhaust elbow it is more resistant to corrosion from the carbon and salt build up than the standard cast iron elbow. However, there is is still the potential of crevice corrosion in the welds for the flange and the injection pipe, although these are less exposed to standing water so the risk is low.

Agree about the superiority of a Vetus  exhaust and that is what I would fit if I was paying, but getting the replacement under warranty rules that out this time. Hopefully the replacement will last the more common longer period.

[artemis]

Cheers I will invest in a plastic one

Mike
Artemis

[dawntreader]

Cheers I will invest in a plastic one

Mike
Artemis

You will need to construct a 'shelf' for it to sit on and make some anchor points to secure it once in place 
(see my photo above - I also used some heat resistant foam to provide some noise reduction on the shelf too)

[Symphony]

You could also consider using the circular NLP type which you can tie down with a cable tie to the bulkhead.

[Clivert]

An idling or slow running engine is a killer for exhausts.
I always give our engine a hard run on high revs for a few minutes on every trip.

[Salty]

Cheers I will invest in a plastic one

Mike
Artemis

You will need to construct a 'shelf' for it to sit on and make some anchor points to secure it once in place 
(see my photo above - I also used some heat resistant foam to provide some noise reduction on the shelf too)

I mounted my cheapo plastic exhaust on a piece of engine compartment foam soundproofing material rescued from a skip and placed on the inside of the hull and laid against the vertical bunk support. The silencer was secured in place using inexpensive adjustable webbing straps with plastic snap together connectors and adjusters. The plastic silencer is very light weight so even with water in it, it doesn’t need anything desperately strong to hold it steady, and the webbing has more than enough strength for that.

[dawntreader]

removed some excess silvered padding from the engine compartment; used thick fishing line (crimped) each end to secure; cut spare piece of 5-ply marine for the shelf. As you say, not heavy so this is adequate (and inexpensive) 

[Craig]

I used expanding polyurethane foam to spray around Vetus exhaust to hold in place. 2 years later, no problems. Job took less than a minute to do. 1/2 hour to buy foam.

Available from Bunnings ( Australia)  B & Q ( Britain) or similar type stores.

While I was at it, used the foam to coat the hot water system, providing additional insulation.

Craig
"Shirley Valentine"
Gold Coast
Australia

[Symphony]

Muffler was replaced yesterday. As expected it was a pinhole in the weld. The new one had very clean looking welds but you can only see the outside and the corrosion starts from the inside in the area of the weld that is submerged in stagnant seawater.

[Boatname]

Um, just found rusty-ish salt water in front of engine bay.

Worked out what it wasn’t ... put tissue in front of muffler, damp after 2 miles.

Which of these two would you recommend and why?

Thanks

https://www.marinesuperstore.com/engine-bay/blowers-exhaust/vetus-waterlock-exhaust

https://www.marinesuperstore.com/general-chandlery/chandlery-misc/vetus-waterlock-lp-30-fixed-inlet

Thinking about it, are the numbers the exhaust inside diameter which is surely the same the exhaust manifold?

Bav 34, 2001, VP 2020D

[Symphony]

The first one - the second does not have enough capacity for your system and the pipes are too small. You need an LP45 as the hose is 45mm diameter. This is virtually a direct replacement for the Volvo muffler, although a bit shorter so you will have to tease the exit exhaust hose to meet the outlet - there is enough slack in the run but it is clamped in places so not easy to move without a bit of fiddling. You will also need to support the watertrap or cushion it as the Volvo mounting points don't suit. There are suggestions on ways of doing this in earlier posts above.

Probably worth having the old one welded up as a spare. I have just organised this for my leaky one.

[Boatname]

Brilliant. Thanks very much 👍

[Salty]

My £56 cheapo no leako no name plastic exhaust muffler purchased from Force 4 chandlery several years ago, is still working a treat. !!