Heat Exchanger Zinc size.

[Carefree Sailor]

Zinc Threads

I use Permatex anti-sieze on the threads. Should be ok, but I am open to opinions.

Here is information from the REALITYCHECK.ME site that may be useful. Notice the 4th bullet. I don't know if using anti-seize would cause a similar problem as using pipe tape.

Sacrificial zinc: Q: Why do you need zinc in the heat exchanger? A: Galvanic corrosion. The zincs are consumed by any electrolytic action that would otherwise corrode your heat exchanger.
Tips:

• Don't wait too long to change or you may end up with zinc chunks in your heat exchanger. If there's nothing on the end of the plug when you remove it, it's been way too long!
• Everyone's zinc change schedule is different, check once a month until you figure out how often yours needs to be changed.
• Replace when about half gone.
• Don't even THINK about putting pipe tape on the end plug threads. The zinc cap pipe threads have to come in contact with the heat exchanger fitting or your zinc is useless.
• Make sure there's rubber gasket material between your heat exchanger and the bracket it sits on to isolate the HX from the engine.
• I read about using a ziplock baggie to catch all the water and the zinc on a forum, that works great. Still use a bunch of shop towels, just in case...
• If you have a replacement end cap you can get just the replacement pencil zinc to screw it into the end cap and save $$.

 

[Christian Williams]

Baby diaper. Absorbs everything.

 

[Frank Langer]

Why the need for a rubber gasket to isolate the heat exchanger from the engine, as suggested in the post above? On our Universal 5416 the heat exchanger sits on a metal flange that has slits in it through which I fit two large hose clamps that hold the heat exchanger snug to the engine. The zinc lasts about 5 months before needing replacement and that has been consistent over ten years. What am I missing by not isolating it from the engine with a rubber gasket?

Frank

 

[Pat C.]

Why the need for a rubber gasket to isolate the heat exchanger from the engine, as suggested in the post above? On our Universal 5416 the heat exchanger sits on a metal flange that has slits in it through which I fit two large hose clamps that hold the heat exchanger snug to the engine. The zinc lasts about 5 months before needing replacement and that has been consistent over ten years. What am I missing by not isolating it from the engine with a rubber gasket?

Frank

To isolate the HX and its zinc from engine and stray galvanic current. Especially if the engine is used as a ground or the electrical system.

 

[Christian Williams]

Good to know. My Hx seems to have old insulation under the attaching bands, and I recall deteriorated rubber "pads" which fell apart last time I had the Hx off. I assumed they were for "vibration". Hmmm.

Wise up!, as John Belushi used to say.

Thanks--

 

[Emerald]

and to really fight galvanic action, we ought to go one step further and make sure all the rubber hoses are marine grade - automotive/non-marine hose may contain what I think of as carbon black, which results in an ability to conduct and hence have galvanic action. So, there is a reason to get the right stuff beyond it just saying "boat" on the side

 

[supersailor]

Heat Exchanger Zinc

Having just finished up the Christmas lights on Terra Nova, I decided it was time to replace the zinc on the heat exchanger. That end of the heat exchanger has been leaking a little. This is my first zinc replacement on boat (it's a little overdue). I thought that the end gasket on the exchanger was leaking but it turns out that the plug on the zinc was the culprit. The plug was only about 1/3 screwed in and, when removed and replaced, would not screw in any farther. I removed the end on the exchanger and found that the threads above that were totally plugged with zinc. Apparently, the previous owner kept using the same plug and eventually stopped removing it and instead went through the end port and unscrewed the old zinc and screwed a new one into it. It still leaked but I guess that was ok. A ream out with a 3/8 NIP tap solved the problem.

The M25XP seems to have used two different heat exchangers. One used the 9/16" plug and one used the 11/16" plug. My best guess is that is what Universal had in stock as the engine was finished. I am lucky and have the larger zinc. If you have the 9/16" plug, the tap needed to clean out the threads is a 1/4 NPT. If you have the 11/16" plug, it is a 3/8 NPT.

I highly recommend that the end cap be removed at the time of replacement. I found that that a couple of the cooling tubes were beginning to plug up but were easy to open up. That might not be the case a year from now.

Of course, while doing the zinc I found that the shaft log had decided to leak excessively recently. Getting to it in the 34 is *##@**#@. It is currently soaking in PB Blaster for removal tomorrow. A priority in the spring is a replacement with a shaft seal.

Catalina Direct has heat exchanger zincs that are exactly the right length. In this case, the length is 1 7/16". They also are selling opening port lenses for the various old Lewmar opening ports that are slightly thicker than OEM. I had a leak in one and this solved the leaking problem. It gave slightly more pressure on the seal. For the size 1, the price was $28.98.