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Old 16-11-2009, 12:22   #1
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Heat Exchanger Problems

Zinc In Heat exchanger.
Hi everyone I have been having problems with electronics’ in my Volvo Pendant MD30 Heat exchanger.
There is no place to install a sacrificial anode (zinc), the Al. housing near the Brass end cap is deter eating.
Is there any value in having a zinc stick just lying horizontally in the sea water at the end of heat exchanger tubes? Between the Brass end cap and tubes. I would have to remove end cap every year and change or add a new one if this worked. The Zinc would partially block some of the tubes but if anything my engine runs cold not hot so I could put up with this.
Or are there any other suggestions. Thanks
Serge
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Old 16-11-2009, 12:47   #2
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Heat exchangers need sacrificial anodes. Add one wherever it will work in the salt water portion of the exchanger. If they did not make provisions for an anode then they did not design it right meaning the heat exchanger is not going to last as long as it could have. You don't want to have to replace this Volvo part. Like all Volvo parts, its going to be very expensive.
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Old 16-11-2009, 13:15   #3
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just laying a zinc in the end of the heat exchanger won't work. In order for this anode to do it's job it needs to be connected (with as little electrical resistance as possible) to the item it is meant to protect. If you're handy, and there's enough sturdy material, you could drill a hole on one of the endplates, tap it for 1/4" npt and install a pencil zinc.
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Old 16-11-2009, 13:47   #4
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Thanks for the advice David
Sailmonky I could drill and tap in the end cap, problem is there is only 1/2'” SPACE between end cap and tubes.. Also you said connect to part I am trying to protect well the end cap made of Brass is fine but it is the Aluminum housing that is suffering. Brass is more Nobel than AL. But most anodes I have seen are usually in the Brass end caps not the housings ???
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Old 16-11-2009, 13:52   #5
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true, but the brass endcaps are connected electrically to the alum in some fashion. the zinc, being also electrically in the circut is less noble than either, so will be sacrificed.
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Old 16-11-2009, 23:27   #6
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Originally Posted by David M View Post
Heat exchangers need sacrificial anodes. Add one wherever it will work in the salt water portion of the exchanger. If they did not make provisions for an anode then they did not design it right meaning the heat exchanger is not going to last as long as it could have. You don't want to have to replace this Volvo part. Like all Volvo parts, its going to be very expensive.
Not necessarily true. I have a 20+ year old Pathfinder engine, and it does not take sacrificial anodes in the heat exchanger.
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Old 17-11-2009, 00:26   #7
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Not necessarily true. I have a 20+ year old Pathfinder engine, and it does not take sacrificial anodes in the heat exchanger.
Ditto!
And my new Yanmar parts list shows no anodes. Your exhaust manifold acts as your anode (less noble). And if yours is aluminum like on yanmars you can expect to buy one every so often.


Galvanic series - Wikipedia, the free encyclopedia
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Old 17-11-2009, 01:59   #8
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Ditto!
And my new Yanmar parts list shows no anodes. Your exhaust manifold acts as your anode (less noble). And if yours is aluminum like on yanmars you can expect to buy one every so often.


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I'm the third owner of our boat, and I don't know the complete history of the engine. I do know I had the engine surveyed before the purchase a few years ago, and had all the deferred maintenance done by a competent yard...none of it involved the heat exchanger. I replaced the anti-freeze not long ago, checked out the exchanger for any possible damage (none present), installed new end boots, and had the tube stack checked out for leaks at a radiator shop that knows heat exchangers. All I had was a few pin holes in the tube stack found during a pressure test, which was easily fixed by running melted solder through the tubes. If I ever do have to replace the heat exchanger or tube, I have another complete unit that was in a basket of parts I bought for $125.00 (very good investment)...same engine as mine.
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Old 17-11-2009, 04:22   #9
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There are avail, line zinc fittings that you can install on the hose to the water pump. It resembles a metal sleve that is pur in the dia to fit inside the hose. Cut the hose, dbl clamp the fitting, install the zinc, attach the grounding wire and you are set. I use on on my refrig water cooler. Bob
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Old 17-11-2009, 08:29   #10
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I'm a little surprised someone would make a heat exchanger with no anode with the dissimilar metals found in one. My Cummins engines for example have one anode in the intercooler and two in the heat exchanger.
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Old 17-11-2009, 21:59   #11
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All good information
The previous owner had the heat exchanger replaced at a cost of $2000.00 I guess about 5 years ago I do not want to do this every 5 years so I am trying to make sure I can stop the present decay. Presently the Brass end cap was supposedly sealing by 2 internal “o” rings one on the inside of end cap and one on the end of aluminum housing. If you can envision the end of the Aluminum housing had an internal “O” ring grove which held the Glycol back and prevented the Salt water from entering. It is this grove that captures the “O” ring that has the outside 1/8” lip that is corroding such that I only have about 80% left.
My first solution is to install a square 1/8” “O” ring on the outside of the housing between the Brass cover and the aluminum lip this will keep the inner ring from bulging out and give some insulation between the 2 dissimilar metals . Now to neutralize any further galvanic action I would like to install a Zinc. It seems like the best approach is to drill and tap the end cap.
Because I do not have much room on the inside of cover I may have to extend outside of cover , I am thinking ½” brass nipple 2 Inches long and somehow screw in 3/8” zinc that would be surrounded by 1/16” salt water all around I hope that as the zinc eats away it does not block the sea water from circulating around the zinc. Any advice or suggestions welcome.
Sorry for being so long winded and I hope the above makes sense.
Thanks everyone
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Old 18-11-2009, 01:47   #12
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I'm a little surprised someone would make a heat exchanger with no anode with the dissimilar metals found in one. My Cummins engines for example have one anode in the intercooler and two in the heat exchanger.
You would have to look at how the system is designed to understand how it works. The entire salt water circuit is, by design, isolated from the engine by the rubber boots and hoses.
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Old 18-11-2009, 09:09   #13
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My question would be are the brass/bronze(?) end caps factory? I would have thought they would be aluminum just like the housing. Personally I'd make some alum. ones. Aluminum is less noble and would erode first. If it's all aluminum then a zink would do its job a lot better.

I know when my alum. heat exchanger goes I'm installing an after market unit that will hold up to the saltwater a lot better. e.g.

Custom & Stock Marine Heat Exchangers & Cooling Systems - Orca, WA
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