Engine Zinc

Ross Fisher · May 11, 2008, 06:42:07 AM

One of the few ( hidden) maintenance issues that I stress about is the zinc anode in the heat exchanger.
Why? I guess because it is difficult to easily check as part of my regular inspections, and also because anything that requires more effort to examine tends to be overlooked until I am really concerned about it's condition.
I checked my anode today ( 11th May 2008), for the first time since September 2007. I was pleased to learn that the anode was no more than 50% sacrificed after 8 months.
I purchased the current anode as a pack of 4 from Catalina Yachts in Australia.
Is the OEM part superior to after market replacements? I can't say for sure, but I am encouraged for my next purchase.
Let's hear your thoughts!

PS: I will install an access door one day soon!

Stu Jackson · May 11, 2008, 10:45:32 AM

The key is the fit of the zinc into the "holder" to assure it stays in place. Zincs are pretty much a commodity, and for this application aren't different, just find the ones that fit.

Speaking of fit, there's been discussion about the proper length of zincs, and some reports about having to cut off the ends of the zincs.

Here's how they work, and the dimensions. I have yet to find a zinc too long that needs to be cut. There's plenty of room in there for a much longer zinc.

We check ours every three months, usually change them out then, sometimes can go six months. There's no reason to overlook this important job if you keep a checklist in your engine maintenance log. If you ignore it, it'll require taking off the HX to find the bits and pieces of the old zinc, which is one heck of a bigger job. Don't stress about it, write it down, and don't ignore it.

Tag: "zinc flix"

Ron Hill · May 11, 2008, 11:55:05 AM

Guys : I have to correct Stu - as all HX innards do NOT look like Stu's!!!
The inside of my heat exchanger has part of the internal "bracing" obstructing a full length Zn going in. If you force it I found that the Zn will break off at the threaded base - which leaves you with practically no Zn protection at all!!

The solution is to take a #2 pencil or wooden dowel the diameter of a Zn and insert it into the threaded hole of the HX. Then note how far up inside it goes. Depending on your HX you'll then know if you have to cut it off or not. I wrote this up in the Mainsheet over 19 years ago.

Stu Jackson · May 11, 2008, 05:12:23 PM

Thanks, Ron. Then the answer, for everyone, is to take your HX off, service it, and figure out what you (YOU) have on YOUR boat, rather than relying on us old geezers. And when you're there, take a picture and show it to us all. Thanks.

Braxton · May 12, 2008, 07:56:43 PM

Is this the right part?

http://shop.torresen.com/ships_store/index.php?p=details&ident=143856&mfc=Universal&sku=301068&prod_name=Universal+Zinc+Anode+3%2F8+NPT+X+1-1%2F2&sectionid=Zincs

I'm new to my boat and I have no idea of my status on this issue. If I go to the trouble of yanking the HX apart I'd like to have a zinc standing by if I need it :)

Stu Jackson · May 12, 2008, 08:35:21 PM

Yes, that's it: Zinc # 301068 is for use on engines with 3" heat exchangers (your 1988 boat makes me believe you have a 3 inch HX on your M25XP).

If you're comfortable with the condition of your HX, you do NOT have to rip it out to replace the zinc. The head of the bolt is 11/16", just get a box end or ratchet on it and away ya go.

For end caps and gaskets, do a search on the word SENDURE and you find the ordering information.

Earl Miller · May 12, 2008, 09:23:29 PM

Stu, is it my imagination or is there a slight taper to the cap on the HX zinc? I have changed mine a number of times and always get a build up of white crystals over time. If this is due to saltwater leaking is it because I have not tightened the cap enough? I have been reluctant to tighten too much for fear of stripping the threads.

If it is tapered there should be a limit to how far it will go in before it jams.

Stu Jackson · May 13, 2008, 12:01:34 AM

Earl, could be, nice analysis photo. Regardless of the type of thread, adjust at insertion to a snug fit so it doesn't back out, but don't over tighten it. I find a half turn with a wrench after it seats well and starts to exhibit some "back-pressure" has been adequate.

Ron Hill · May 13, 2008, 02:44:42 PM

Earl : Yes, there is a taper - as it a tapered pipe thread!!

Guys : The base is reusable, all you need to do is clean it up with Lime-A-Way and buy another piece of Zn and screw it in.
I'd also recommend that you use a battery terminal cleaning brush (with a male & female wire brushes) to clean the female threads in the HX the terminal female brush to clean the threaded holder. A thought.

Mark Elkin · May 17, 2008, 10:47:25 PM

Quote from: Stu Jackson on May 11, 2008, 10:45:32 AM
We check ours every three months, usually change them out then, sometimes can go six months. There's no reason to overlook this important job if you keep a checklist in your engine maintenance log. If you ignore it, it'll require taking off the HX to find the bits and pieces of the old zinc, which is one heck of a bigger job. Don't stress about it, write it down, and don't ignore it.

Folks, I absolutely second Stu (or is that Stud?) on this. Yes, it is a pain to access it, but with practice it gets to be second nature.

Do NOT ignore your zinc. I learned the hard (i.e. expensive) way what can happen when you ignore it. Your results may vary, but in my case, a pin hole leak developed inside the HX and salt water began mixing into my fresh water side. And eventually the salt caked up in the thermostat and then the engine ran so hot that all I saw was steam leaving the raw water exhaust. I replaced the HX, the thermostat, flushed the fresh water side a zillion times with "salt away" and had a mechanic check for other damage. All that because it was a pain to check the zinc. Now I got "EZ" religion. (EZ = engine zinc).