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Old 19-07-2006, 09:58   #1
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Join Date: Jun 2005
Location: Nova Scotia
Boat: Morgan 382 "Tropical Wave"
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Heat Exchanger Anode

We recently aquired a 1980 Morgan 382 equipped with a Perkins 4-108 diesel. The boat has not been well maintained for probably 5-6 years, and has been on the hard for 2 years. A survey conducted Aug 2004 talked about signs of corrosion in the rudder shoe, and in fact that was replaced by the PO. The boat also has a new cutlass bearing, PSS seal, reconditioned prop and what might be a new shaft. So I suspect there have been some major corrosion problems with this boat.

According to the engine surveyor and to the Perkins operations manual (not the shop manual) there is an anode in the heat exchanger. When I remove the plug where the anode should be, the hole seems to be plugged solid. I can't see into the hole because of it's location (on the back of one end of the transverse-mounter heat exchanger), but I can scrape some material out with my fingernail.

My question is, does this indicate that the heat exchanger is full of corrosion? Has the anode disintegrated? or was the surveyor mistaken in saying theere should be an anode in there? some of these boats seem to have anodes, but some don't.

We are about to launch the boat in 8 days, and I want to know if I need to remove the heat exchanger and get it cleaned, or is this a normal situation?


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Old 19-07-2006, 10:32   #2
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Is the stuff blocking the hole relatively soft? If so, I suspect it is the remainder of the zinc anode that broke of from the bronze plug. This is common. If you take the end cap off of the heat exchanger, you should be able to push the zinc into the exchanger and pull it out the end. Alternately, you can probably use a pick or something to crumble it out the hole it is stuck in.

The exchanger usually doesn't get corroded. Rather it can get a lot of salts deposits on it over time that reduce its capacity for exchanging heat with the fresh water side. The usual symptoms are the engine gradually running hotter than normal, or starting to overheat at higher rpms or loads.

If you don't want to remove your heat exchanger for inspection, simply remove the remaining zinc, replace it with a new one and see if the engine runs at its rated temperature. If so, go ahead for now.

It is a good idea to visually inspect the heat exchanger at some point, though - just for peace of mind. They don't salt up very easily if the engine has been run regularly at its normal temperatures. If it is salted, cleaning them is fairly easy. Just remove it and soak it in a bucket of Marsolve or similar scale remover.

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Old 19-07-2006, 11:31   #3

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Been there.... done that!

I had the same situation when I took first went looking for the anode after buying my boat with a 30 year old Westerbeke 4-154. Not only had the zinc dissolved, but the brass nut that held it in place had de-zincified and turned to a soft copper sponge that just crumbled under the wrench!

After disassembling everything and cleaning the heat exchangeer tubes, I had to chase the threads for the anode with a pipe tape to get things back to rights. The heat exchanger suffered significant corrosion, but survived leak free, at least for now.

The plan is to pull the current one and put in a new one before our extended cruise. I'll keep the old one as a spare, or maybe not. Not the kind of thing that fails prematurely if taken care of.

By the way, I can't fault the former owner too much, the zincs are barely mentioned anywhere in the engine manuals. The only place they are discussed is in the shop manuals, and there they are in the winterization chapter. Not a section of the manual often reviewed for a boat in an area with a twelve month sailing season!
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Old 19-07-2006, 13:51   #4
Bob Norson

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I had a perkins 4-236.. the original manifold didn't use a conventional anode. The end plate on the cold side was sacrificial. Where I ran into trouble was the previous owner had replaced the original factory type end plate with a plain SS plate. The manifold became clogged with a heavy, crusty black substance that when removed took a lot of the mainfold with it. It started to leak soon after and I replaced it with an after market thing that used conventional anode. The cast iron thing may have been on there for 30 years before all this.

Corrosion along prop and shaft is more likely electric current leak.

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