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Diesel This is a new forum dedicated to diesel engines and their applicable accessories.


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Old 08-31-2012
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Heat Exchanger Zinc Issues/Questions

Hello All,

I have tried to replace the heat exchanger zinc for the first time in my new-to-me Catalina 28 with a Universal M25-XP, and have encountered something which I didn't quite expect. I expected water to come out when removing the zinc drain plug, but when the zinc was removed, engine coolant came out. Is this normal? Should I have expected this? If so, would it stop once the amount in the heat exchanger emptied, or would it keep emptying until all coolant (not just that within the heat exchanger) emptied?

Also, the zinc I had (7/16 wrench) would not fit. The wrench size was correct, it appeared that it was too long. This one was 2 inches I believe. Barely any of it would fit, and I ended up putting the old brass plug back in...which is zinc-less. Is there something obstructing this zinc, such as old, broken off zincs, or is this zinc to long and needs to be cut. If needs to be cut, does anyone know the correct length? Or do I just cut it until it fits...

Lastly, if there is an obstruction blocking the new zinc (i.e. broken off zinc)...should I remove the endplates? I know new seals would be needed, but what else would need to be done? Would I only need to empty the heat exchanger of all liquid (this kinda ties into the first question above about engine coolant).

I don't know why something seemingly so simple has become so difficult...but between getting the wrong zinc sizes, and now this...replacing this zinc has become my nemesis...and I can only imagine what awaits later...

Thanks,

Brian
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Old 08-31-2012
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Re: Heat Exchanger Zinc Issues/Questions

Brian,

According to this site...it's possible that you could have the wrong size zinc. Apparently there are two different sizes used for Universal engines. So before I took off the end caps, I'd measure the diameter of your exchanger and make sure you have the right part # .

Universal Zinc Anode 3/8 NPT X 1-1/2 Universal 301068 Sailboat Supplies, Engine Parts and Boat Parts

Looking at the sketch of your engine.. The zinc and the heat exchanger drain appear to be one and the same, and on the bottom. So yes, it appears that you will lose some coolant..if you don't work fast you may lose alot. On my Westerbeake the zinc is installed from the top of the exchanger, so I can change or inspect it without losing anything. There's a seperate drain on the bottom.
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Re: Heat Exchanger Zinc Issues/Questions

Thanks for the reply...this is all new to me, so questions abound. Concerning losing coolant...would I just lose what is in the heat exchanger, or could I potentially lose all of the coolant from the system? Also, if I wanted to take the end caps off to check for loose zinc pieces, I'm guessing I need to drain the heat exchanger first, correct? If I need to replace some coolant, do I need to be concerned about bleeding the system, or can I simply add some more of the same mix?

Thanks again!
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Re: Heat Exchanger Zinc Issues/Questions

The zinc should be in the salt water circuit. So there are two possibilities : you have coolant in the salt water circuit (not good), or you removed the wrong thing. Is there maybe a drain plug in the HX for the fresh water circuit?

The zinc plug on my HX is near the end plug, about 2" in, in the side of the HX.

I have the 5424 (more or less the same engine) and got the wrong zinc dia when I mail ordered it. What was successful was to take the old one to my local chandler and match it. Cost about $1 for just the zinc, or $3 with the nut. I was expecting to have to cut the 1.5" long zinc down, but did not.

Don't take the end caps off, you'll need new gaskets to make them seal again.

Can you take a pic of the nut you removed?
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Last edited by MarkSF; 08-31-2012 at 05:12 PM.
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Re: Heat Exchanger Zinc Issues/Questions

When you remove the zinc there should not be coolant in liquid that runs out. The zinc is installed in the raw water side of the heat exchanger. If you are getting coolant there is a leak between the two systems. Not a good thing at all. You will need to check this out.
I have always bought my replacement zincs at West and have only seen them in one length. Everytime I have replaced the zinc the old one broke off and I have had to remove the end plate to retrieve the broken piece. I would suspect that that is what is blocking the new zinc. The end plate gasket is rubber so it has not been a problem for me to re-use.

Last edited by ebs001; 08-31-2012 at 05:03 PM.
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Re: Heat Exchanger Zinc Issues/Questions

A bit of searching and I found this :

Autopsy A Westerbeke / Universal Marine Heat Exchanger Photo Gallery by Compass Marine at pbase.com

Does show how it is possible for a new zinc to not fit, if you have crud like that.

What you saw could have been salt water that's turned blue from the brass and copper HX components corroding, not coolant. The salt water in that pic looks slightly blue, too.

I take back what I said about not taking the end off, looks like a good idea!
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Old 08-31-2012
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Re: Heat Exchanger Zinc Issues/Questions

Disconnect all 4 hoses from your HX and put it in a bucket. Plug the anti-freeze coolant plugs with something to keep it from seeping out.
Take the HX out of the engine compartment to somewhere you can safely and easily work on it.
Remove the end cap nearest where the zinc is. Check for obvious leaks and obstructions and flush out the inside of the HX with water. You might very well find a mess of old corroded zincs in there as shown in MaineSail's illuminating photo.

You do need to have the correct sized zinc/nut for your HX on hand. They only come in fairly standard sizes. WM should carry them. I bought a few sizes at CatalinaDirect when I did this procedure with my friends HX on his 5424 diesel.

If you want to be really anal then clean the outside of the HX and give it a quick coat of new paint. This will allow you to see if/where any leaks develop.

This should not be such a difficult job to do.
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Old 09-01-2012
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Re: Heat Exchanger Zinc Issues/Questions

Thanks for the responses everyone. I'm heading down there tomorrow so will head all the above advice. The plug I removed was on the starboard side on the bottom. Looked excactly like the zinc plug with the nut welded onto it...with one exception...when looking at engine diagrams for the M25-XP, it appears the zinc should be on the port side! I will investigate further...it is entirely possible I was removing the wrong thing, if there is something such as a drain plug for coolant.

The coolant was an orange color...so I'm fairly certain it was the coolant. However, with my exceptionally limited experience with all things mechanical...you never know.

i'm pretty knew here, but I am always amazed at the genorousity of others in trying to assist others...

Thanks again...
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Old 09-01-2012
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Re: Heat Exchanger Zinc Issues/Questions

I was a bit confused by the drawings I found of your exchanger too. My exchanger is almost exactly like the one in Maine Sail's photos. I have two drains on the bottom: one for the raw water side, one for the fresh/coolant side. The zinc goes in from the top, ( not a drain) in the 4th chamber of the raw water side. ( a four pass system) So when I inspect or change it, I don't lose anything. There are four hoses..in and out for the Coolant side, and in and out for the raw water.

When I looked at the drawings of your unit ( or what I thought was your unit) it only showed one drain with the zinc as part of it.

New Page 1

I have found that my westerbeake drawings don't always reflect the reality. So, it might be helpful if you took some pictures.
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Last edited by Tempest; 09-01-2012 at 10:58 AM.
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