Volvo Penta Heat Exchanger corrosion poll - please help

[Beneteau381]

Mine looked like this:

A really good local engineering shop built it up like this, carefully managing the temperature so as to not split the casting:

And then "scraped" it flat:

For those wondering...

Bootiful job!

 

[bbs]

I have a similar looking issue with my 2006 Volvo Penta D2-55 C and believe I'm faced with replacing the entire heat exchanger (>$5K for the parts).

This is what the heat exchanger exhaust looked like after removing the riser/exhaust elbow, with the flange still in place. Note the loose pile of what I guess is some kind of calcification sitting just inside the heat exchanger exhaust out.

And here it is with the flange removed and after a quick vacuum job:

The riser and flange were both replaced in 2017 (not by me). The riser is fairly corroded and needs replacing again:
View attachment 167761View attachment 167762


This flange is in decent shape:

View attachment 167763View attachment 167764


I'm not entirely sure what kind of corrosion I'm looking at in the heat exchanger exhaust, but I don't believe this all happened since the 2017 riser replacement. Before I shell out $5K for a new heat exchanger, which seems to be the only course of action here, I'd like to develop a theory for how it got so bad.

Do you all think this is simply the result of the riser not getting replaced regularly enough leading to salt water getting blown back there and getting stuck?

Thank you

 

[MagicalArmchair]

This is exactly the same situation I was in. The reason this happens, in Volvos own words, is:

"Galvanic corrosion is caused by two dissimilar metals which are in direct physical contact with each other and are immersed in an electrolyte (a liquid that conducts electricity, such as sea water). The joint between the exhaust elbow and exhaust manifold is not in a solution of sea water, the sea water is injected at a lower point into the exhaust stream. We believe the corrosion of the exhaust elbow and manifold is due to moist air mixing with elements in the exhaust gases to form a solution that over time can cause corrosion. Hence our point this failure is age related. At the end of the boating season we suggest points to check in addition to the annual servicing, VP workshops will have access to this information."

You do not need to replace the heat exchanger. Drain the coolant, drop the heat exchanger off, take it to a specialist aluminium welder who can build the flange back up. They can then either "Scrape" it flat or have it machined flat, pressure test it, and then refit!

I'm currently in the process of writing this up, bit by bit for an article for PBO.

 

[bbs]

Thank you for the quick reply. I didn't realize the heat exchanger is made out of aluminum. So I should expect this to continue corroding even after a fix/replacement? Have you found any suggested ways of mitigating this connection point of dissimilar metals going forward? Seems like a pretty major "consumable" to have in the system.

One thing that is puzzling to me is that the corrosion continues inside the heat exchanger exhaust on the bottom side to an area where there is nothing else touching it. There is just a chunk of the heat exchanger exhaust missing leading up mating surface that is also corroding from it's contact with the gasket. I'm not sure how far away from the contact point of the dissimilar metals I should expect to see corrosion, but it seems pretty far away.

 

[MagicalArmchair]

Thank you for the quick reply. I didn't realize the heat exchanger is made out of aluminum. So I should expect this to continue corroding even after a fix/replacement? Have you found any suggested ways of mitigating this connection point of dissimilar metals going forward? Seems like a pretty major "consumable" to have in the system.

One thing that is puzzling to me is that the corrosion continues inside the heat exchanger exhaust on the bottom side to an area where there is nothing else touching it. There is just a chunk of the heat exchanger exhaust missing leading up mating surface that is also corroding from it's contact with the gasket. I'm not sure how far away from the contact point of the dissimilar metals I should expect to see corrosion, but it seems pretty far away.

The guys at Parts4Engines have thought of that and with their exhaust elbow they provide a composite gasket. This creates a non conductive barrier between the stainless and the aluminium meaning - at least in theory - there should be no more corrosion ever again.

I've had mine on for two years now since the repair, so I should drop my exhaust elbow off this year and inspect it - I'm hoping all looks well!!

 

[Rbs]

The guys at Parts4Engines have thought of that and with their exhaust elbow they provide a composite gasket. This creates a non conductive barrier between the stainless and the aluminium meaning - at least in theory - there should be no more corrosion ever again.

I've had mine on for two years now since the repair, so I should drop my exhaust elbow off this year and inspect it - I'm hoping all looks well!!

The parts are still in contact because of the studs/nuts that hold the exhaust mixer to the exhaust manifold.

If salt saltwater bridges the gap where the gasket is, a circuit will be created between the dissimilar metals through the metal studs.

For this to be avoided the studs need to be insulated. There two other examples of this insulation on the D1 and D2 engines. (a) the hx copper insert is isolated with o-rings and plastic end caps. (b) the sail drive is isolated from the engine with non conducting washers and inserts.

It's interesting that VP did not design isolation into these components, but I feel that the reality is that water should not be able to get back into the exhaust mixer. The fact it can, points to a fault with the installation of the exhaust system.

I have seen installs where this corrosion has never happened. And I have seen installs where it has happened. In each case of corrosion the exhaust system has been less than ideal.

 

[MagicalArmchair]

The parts are still in contact because of the studs/nuts that hold the exhaust mixer to the exhaust manifold.

If salt saltwater bridges the gap where the gasket is, a circuit will be created between the dissimilar metals through the metal studs.

For this to be avoided the studs need to be insulated. There two other examples of this insulation on the D1 and D2 engines. (a) the hx copper insert is isolated with o-rings and plastic end caps. (b) the sail drive is isolated from the engine with non conducting washers and inserts.

It's interesting that VP did not design isolation into these components, but I feel that the reality is that water should not be able to get back into the exhaust mixer. The fact it can, points to a fault with the installation of the exhaust system.

I have seen installs where this corrosion has never happened. And I have seen installs where it has happened. In each case of corrosion the exhaust system has been less than ideal.

Ha, yes, I had never considered that. The studs will still create a gavalnic circuit! I guess you could put TefGel onto the studs, thus insulating them from either the heat exchanger or the exhaust elbow? I don't think I put that on either end you know... ideally you would put it at both ends... I had best inspect this winter then.

The cause of the water getting back to this point is usually the water injection point becoming rusty and thus "squirting" and splashing back up the elbow. And that with condensation is enough to create this behavior I think.

 

[RoSea22]

Hello all, same problem here only D2-55A. I wonder if I should insulate the for studs by opening the flange holes to 10.5mm and inserting some PTFE pipes und Washers to minimise the risk of galvanic corrosion. Any thoughts on that matter? Thanks in advance.

 

[Rbs]

Hello all, same problem here only D2-55A. I wonder if I should insulate the for studs by opening the flange holes to 10.5mm and inserting some PTFE pipes und Washers to minimise the risk of galvanic corrosion. Any thoughts on that matter? Thanks in advance.

If it is galvanic corrosion.
It's more likely exhaust gases mixing with sea water creating a liquid that is corrosive to Alluminium.
The question is how is water getting in there in the first place.

 

[RoSea22]

If it is galvanic corrosion.
It's more likely exhaust gases mixing with sea water creating a liquid that is corrosive to Alluminium.
The question is how is water getting in there in the first place.

I guess it's because the exhaust elbow was clogged before. Thus spraying seawater in all directions. Others point out there is a design flaw. I cleaned the elbow now as good as possible and want to switch to a stainless one next year.
Need an idea how to isolate the studs from the stainless elbow.

 

[MagicalArmchair]

After three years, I've popped the new stainless elbow off.

Note, the studs are not galvanically isolated in anyway right now, and they appear ok.

With the gasket on:

Gasket removed:

Closeup of the Studs:

What was most alarming was the bolts holding the water injection elbow onto the exhaus elbow itself. I hadn't realised they had supplied mild steel bolts, so these had nearly corroded clean through. I will be replacing these with SS ones!

In summary, there is some white dust that indicates some galvanic process, but no appreciable corrosion or lost material as such. Anything I can put on here that will withstand the temperatures? I could put TefGel on the studs, that is rated to 280 degrees, and I think it should survive where it is? Could I smear that on the gasket? Or will that just burn off?

 

[Krumelur]

Mine looked like this:

A really good local engineering shop built it up like this, carefully managing the temperature so as to not split the casting:

And then "scraped" it flat:

For those wondering...

Hi,

I'm new to the forum and I came here because of this thread. My D2-55F has similar issues. I recently replaced the mixing elbow with a stainless steel version from HDI marine. But i would like to have my heat exchanger fixed like yours. Can you share who did this fantastic job? Given a new exchanger will cost me €4.500, I would not mind shipping mine to the UK or even going there personally to have it fixed at the specialist you used.

 

[MagicalArmchair]

Hello, it was an outfit called GoToEngineering, however, when I look for their details now I can't find them. I wonder if they have rebranded or moved?

Look for a local aluminium welding company and then take the exchanger to them to talk the fix over with them. I've written the whole adventure up for PBO, and I think it'll be in the magazine later this year.

Good luck and report back how you get on.