Volvo Penta D2 55 Corrosion at Sea-Water Injection Elbow and Heat-Exchanger

[s/y Susanne]

Anyone with D2-55 + Saildrive set-up should regularly check the sea-water injection elbow immediately aft of the Heat Exchanger on the port side of the engine. Inspect for any evidence of salt crystals at the gasket for the following reason:

The elbow is a hollow casting with 3 core plugs. Internally the cast iron corrodes as it is hot and wet and passes warm sea-water! The scabs of iron oxide build up inside the elbow. These can block the water injector ports ( one on top and one below)  In this process its quite possible for pumped sea-water to spray backwards toward the exhaust manifold.

The resultant hot sea-water corrodes the aluminium all around the flange to the elbow, eventually it will leak EXHAUST GASES into the engine bay.

I would recommend anyone with this set-up to remove the four bolts attaching the elbow and lifting lug and have a good look at the state of the aluminium on the manifold/heat-exchanger  and the elbow to satisfy themselves that they are not about to gas anyone sleeping in the aft berths.

In my case a scrape at a "salt-blister" while inspecting the overall condition of the engine  revealed a pea-sized hole which then leaked exhaust  gases ( and sparks) when the engine was fired up.

MOTA, the maker of the heat-exchanger, have not replied to a simple emergency question on the choice of welding rod necessary to make an emergency repair.  Another unhappy user!

It is also possible that electrolysis is partially responsible for the loss of aluminium as three metals join at this point, Aluminium, Stainless Steel ( Gasket) and Cast Iron.

Owners beware!

[PEA-JAY]

Thank you for your warning re exhaust elbow. This could not have been better timed as far as I'm concerned! I recently returned to my pontoon berth after 4 months on the hard and noticed that at full revs the exhaust sound changed from a water muffled one to a dry one, revs 22 - 2500 cruising all normal- full out 3000 sound changes. I examined the raw water pump (ok) and flushed out the heat exchanger from salt deposits using a weak solution of sulphamic acid + water heated to about 50 deg.C which cured the exhaust sound problem. To finish off I removed the exhaust elbow to clean it. As I removed the salt and rust build up the internal pipe partly disintegrated! The elbow is still useable however "super Mario", my engineer friend, suggested we fabricate a stainless steel replacement. He did this successfully on my previous boat, a Moody 376, powered by a 35hp Thornycroft (Mitsubishi). My question to my forum friends is . . . will so many dissimilar metals end up in one very expensive pile of white dust? I appreciate any advise I receive before deciding either way.

[s/y Susanne]

Pea-Jay

I would be happy to buy a well fabricated S/S replacement elbow as a replacement for this piece of **** from VP. I have made some enquiries in US as the same  issue clearly affects other VP models as well as other makes of marine diesels.

The best I have seen so far does not fit the D2-55 but is made by proper "investment casting" of Stainless Steel to produce something that should not cause this predictable problem. Other products fabricated from welded tube may have to suffice if there is no alternative but I will keep on digging and report back. Anyone else??

[Spirit of Mary]

SS steel is not necessarily better than cast iron. It depends on the type of stainless steel. 316 is the minimum, but is sensitive to pitting corrosion and stress corrosion at the welds in this environment (salt water at higher temperature combined with exhaust gasses). 904 would be a better choice as well as duplex SS. Normally the cast iron versions last about 8 - 15 years depending on the use and are better to be replaced preventative or checked regularly when the life is about 10 years.
There are SS elbows available for VP maybe at a lower price than the original cast iron ones from VP.
See: www.keypart.com/stock/861906ss-r
Ger

[The Other Woman]

S/Y Susanne you?re too late for me. 

Bavaria 36 Year 2000 Engine MD2030C

After being on the hard we launched early April. On starting the engine water was coming out the exhaust but then the sound from the exhaust became louder no water was flowing.
I fit a new impeller but water was still not flowing. On closer investigation when the pipe was removed from the inflow of the intercooler, water flowed but exhaust gases where coming back through the intercooler, so the pump could not over come the pressure.
Then I noticed there was no water in the engine cooling and I had checked this 1 hour before.
The problem was the aluminium heat exchanger body had blown a hole near the exhaust elbow and water was just running into the exhaust out of the engine. Volvo?s price for replacement £2000.00 .  So had a mate to weld it up for me £60 .
 
Then on looking at the elbow it had total broken up on the inner sleeve, this made it easy for the back pressers to be directed up back across the heat exchange not allowing water to flow. Have now made a 316l stainless steel elbow . 

Therefore I agree with S/Y Susanne you have to keep an eye on the elbow . I will be taking the elbow off every year when winterising just to clean and observe and would suggest some boat owners would be shocked at what they saw as these elbows are not just on Bavaria boats .

Mick

[s/y Susanne]

I have now fitted an Investment Cast Stainless Steel elbow  which is a direct replacement for the OEM (Perkins) elbow. It clearly works well and is the same cast weight as the original so no welds to corrode and plenty of sacrificial meat should the stainless fail to deliver on "non-corrosible" aspects of itself.

Apart from being a simple straightforward swap the engine now has a much more sonorous and gentle "burbling" exhaust note!

Why an engine manufacturer, knowing the conditions that a component like this has to face in use manufacture, would use such a poor choice of materials such a plain cast iron I am not sure. The cynical might suggest that the spares aftermarket is more profitable than the original supply to the yacht-builder.  Given the retail price of many Penta spares there is clearly room in the trough for more than one nose.

Stewart
SY Susanne

[Salty]

Thanks guys for the tip off, particularly Spirit of Mary for the advice on longevity, materials and the keypart link.

[Craig]

I have a D1-30 and as yet, have not had this problem. I have however  met a number of owners that have had this problem. It is a problem of MOST if not ALL VP engines. Yanmars and other makes also have similar problems.

Generally the elbow will last between 5 and 10 years depending on time on the hard and whether you flush with fresh water before the winter lay up.

After discussing Volvo maintenance issues with Volvo agents in Greece and Malta and the Volvo Technical Rep at the Dusseldorf Boat Show a few years ago the maintenance issues that stuck in my mind were:-
1. Most common problem is always the salt water impellor. You will lose blades if you run engine for as short as 30 sec without water!!!
2. When you take off the lid to clean the salt water strainer make sure you have the salt water inlet closed to retain salt water in the line to ensure you do not suck air for too long.
3. The salt water impellor shaft seals are very vulnerable to running dry. A soon as you notice water or oil dripping out of the small hole behind the salt water impellor replace the bearings and seals. If you delay you will also have to replace the shaft.
4. Always flush the salt water system using fresh water, or preferably water containing an anti-corrosion additive before laying up or even leaving the boat for more than a couple of months.
5. The exhaust elbow is the most common replacement part ( other and regular maintenance items) in most Volvos. This is where corrosion causes the most damage. There is no sacrificial anodes in new Volvo engines so there is a reluctance to use stainless steel in replacement parts. I do note that there are a number of suppliers of custom stainless steel exhaust elbows and I know of boats with these fitted for many years that appear to have no problems. I am uncertain as to whether to go for a SS replacement when I eventually need a replacement.
6. A common problem is leaking oil seals and the common cause of this is overfilling with oil. The Oil level should be between the High and Low mark. It is not like a car where the High Level is where you fill up to when the oil gets down to the Low level. Going above the High level is easy to do and will cause problems.
7. Heat exchangers will also corrode. Most heat exchangers can be removed fairly easily from the exhaust end for inspection and cleaning. I had a calcium build-up in mine from 5 years sailing in the Med but no corrosion as such.   
8. Make sure you have a method of disconnecting the Hot Water Heater in your boat from the engine heating. The heat exchanger in your heating tank for the boat's hot water is a common cause of corrosion. You may drain your engine fresh water into your domestic hot water system or, if you leave the fresh water pump on, push the boat's fresh water back into the engine coolant and out through the plastic fill tank on top of your engine. This is likely to occur if you drain your fresh water tanks overwinter and then motor before filling your fresh water tanks. ( Guess how I know this!!!!)
9. Diesel bug is the main problem stopping engines at sea that is difficult to remedy at sea.
10, If you do regular maintenance ( oil, filters etc.)  you are unlikely to have any mechanical problems other than the above, ever. Your motor should outlast you. 

My comments above ignore electrical issues that are another can of worms. Hope I haven't bored you guys too much.

Craig
s/v "Shirley Valentine"