pitting on engine

[stanirvin]

I have a 33 ft Hunter sailboat with a fairly new (360 hours) Vetus 3.09 diesel engine.
Lately I've noticed some pitting on the heat exchanger housing. There are two small eruptions that don't go all the way through the aluminum housing, but they are getting bigger. The gray material (aluminum?) can be easily wiped off but they come back. Could there be an electrolysis issue here? Any thoughts or fixes?
thanks,
Stan

[Montanan]

Originally Posted by stanirvin

I have a 33 ft Hunter sailboat with a fairly new (360 hours) Vetus 3.09 diesel engine.
Lately I've noticed some pitting on the heat exchanger housing. There are two small eruptions that don't go all the way through the aluminum housing, but they are getting bigger. The gray material (aluminum?) can be easily wiped off but they come back. Could there be an electrolysis issue here? Any thoughts or fixes?
thanks,
Stan

Yes there could also be galvanic corrosion, check the condition of its sacrificial anode.

https://www.marinedieselbasics.com/m...changer-anode/


A bit confused though, is the pitting that you are referencing on the outside [air side] or the water side of the housing?

Background reference for aluminum pitting.

https://aluminium-guide.com/en/toche...ya-alyuminiya/

[boatpoker]

No. It is not "electrolysis". Electrolysis is a different process entirely and does not occur on boats. No one trained in Marine Corrosion would use that term.

It is possible that it is galvanic corrosion that is being enhanced by a low qualtiy casting with occlusions. that would account for the aluminum oxide (white powder). What is the condition of the anode in the heat exchanger ?

There is a remote chance that it could be stray current causing the corrosion but would need a lot more info and phots to make what could only be a guess without testing.

You might want to contact an ABYC Certified Corrosion technichian to track down the issue.

... retired Certified Marine Corrosion Analyst.

[Lepke]

Probably impurities in the casting. Aluminum can be welded, do it before it goes all the way thru.

[stanirvin]

Originally Posted by Montanan

Yes there could also be galvanic corrosion, check the condition of its sacrificial anode.

https://www.marinedieselbasics.com/m...changer-anode/


A bit confused though, is the pitting that you are referencing on the outside [air side] or the water side of the housing?

Background reference for aluminum pitting.

https://aluminium-guide.com/en/toche...ya-alyuminiya/

The pitting is on the outside (air side) of the aluminum cover.

[stanirvin]

The pitting is on the outside of the aluminum cover. The gray material is wet, not a powder. The pits are probably 1/16" deep. Iv'e tried aluminum weld but it eventually falls out due I think to the vibration of the engine. I change the prop shaft anode regularly, but if there is an engine anode, I cant find it. Is it likely there is one in the heat exchanger?
thanks again,
Stan

[stanirvin]

Originally Posted by Lepke

Probably impurities in the casting. Aluminum can be welded, do it before it goes all the way thru.

How is it possible to weld around an engine without the risk of fire from fuel?
Would I need to remove the heat exchanger to do that?
thanks,
Stan

[Reefmagnet]

It would seem to me that you have a casting with porosity defects. You can't fix it with an in situ repair, imo. It needs to be removed, cleaned and welded (or braze) repaired.

[boatpoker]

Originally Posted by stanirvin

The pitting is on the outside of the aluminum cover. The gray material is wet, not a powder. The pits are probably 1/16" deep. Iv'e tried aluminum weld but it eventually falls out due I think to the vibration of the engine. I change the prop shaft anode regularly, but if there is an engine anode, I cant find it. Is it likely there is one in the heat exchanger?
thanks again,
Stan

Most heat exchangers do have one or more anodes (mine has two).