Engine Zinc Blocked

Outrageous · #1 01-20-2013

Went to change my engine zinc in year 3+ of ownership. It unscrewed and the brass cap came off. When I tried to put in the replacement, it would not go. I felt around with a finger, then screwdriver, and there's something up there - I'm thinking the partially corroded zincs from prior years (the zinc part screws into the brass hex nut cap, and I'm guessing it corrodes itself out of the cap socket). I can't get the new one in, and I can't get the cap to screw fully on. I noted a bolt on the side of the heat exchanger, and I thought I could remove that bolt and pull off the side and see what's blocking things. The bolt came out easily, but the side did not - at which point I decided to put the bolt back, and Ask The Experts, rather than forcing things.

I ran the engine successfully after putting things back together and noted no leaks and proper exhaust water, but I'd feel better with a new zinc and a cap screwed on fully. See attached photos. Engine is a universal diesel M25-XPA with 695 hours. I have the original manual, and one is online here: http://www.westerbeke.com/OnlineManu...erator_man.pdf

At start and end of Year 1 this replacement went fine, though I noticed some shards of prior zincs. At the end of year 1 I installed a galvanic isolator, and made a note wondering if the zincs would last longer. My notes show the zinc was down ~1/2 at end of year 2. So the questions are:

1. how should I investigate this further without damaging things?
2. should I expect that my zinc from prior years to last much longer?
3. what risk am I taking just leaving things alone for another X months, and trying again?

Thanks for your support.

CalebD · #2 01-20-2013

Check out this tutorial on HXs: Autopsy A Westerbeke / Universal Marine Heat Exchanger Photo Gallery by Compass Marine at pbase.com

You are going to need to clean out the inside of your HX (as shown in link) AND you should change that zinc more often than every 3 years. Yearly changes may not even be frequent enough.

It is easiest to remove the HX from the engine compartment and work on it elsewhere.

dugsmith98 · #3 01-21-2013

I have a westerbeke 44 and the same style of heat exchanger. Remove the end cap screw on the heat exchanger. Put a thin flat edge screwdriver to pry off the end cap, and it should just pop off. You can then clean out the dead zinc that is plugging your bottom hole. Fresh gaskets wouldn't hurt either. The zinc is on one end of the heat exchanger and the other end is where you will find the pieces from the raw water impeller, if that ever fails. Having a pair of gaskets, a new zinc or two, and a couple of impellers should make sense. Once you get it apart, it will be easier to see what your drawing is showing you.

Outrageous · #4 01-23-2013

Thanks to both of you for those pointed directions, we have Partial Success. I was able to get the end cap off, and use needle nose pliers to remove lots of leftover zinc. Having a telescoping, pivoting mirror was essential. I could not get the new zinc in, which is leading me to question whether the specified size is correct. I had a smaller zinc which I was able to thread into the brass end cap, but it still would not screw in. As I was able to screw the cap on WITHOUT a zinc in it, I determined some zinc deposits must be left in the hole. I used an allen wrench (the short end of the L) to scrape both inside the exchanger and up thru the threaded entryway - freeing more hard deposits - until I was able to get the cap with the small zinc screwed in. After reassembly, engine tested with no leaks and with proper exhaust water.

I made a note to check the zinc in 4 months. I will look for some type of wire bottle brush which I might use to scrub off more zinc without damaging the threads. I am left with the following questions:

Is the engine corrosion-safe with just lumps of zinc left, rather than an assembled anode?
Is the zinc supposed to be leeched away and purged with the exhaust?
Given that I have a galvanic isolator, how often should I be checking the zinc?
Why did I have so much zinc in there? I'm changing too often (approx annually), and the isolator is retarding galvanic loss? Or what?
Do you replace the zinc as soon as it starts to flake off, or wait until it disappears/detaches from the cap, or wait until there's no lumps of zinc in the HX?

I've used that Maine guy for other stuff, he's great. Thank the Lord he has a Universal M-25 - that will come in handy forever. Apologies for not checking there first.

Geoff54 · #5 01-23-2013

I won't try to answer your questions because my knowledge in this area extends to "check regularly, replace as necessary". However, these might be of interest to you. I have found multiple uses for them and at seven bucks, they can be regarded as disposable.

10 Piece Tube Brush Kit

dugsmith98 · #6 01-23-2013

You really do need some zinc in the raw water cooling system, even with a galvanic isolator. So a small metal wire brush, or figure out what size threads they are supposed to be (pull the old zinc and bolt to see what they are) and run a tap back through to clear the crud out of the current threads. My boat is 9 years old and after about 9 months the zinc pencil is about 75% shot. But I don't have any real corrosion on the threads, so yours sounds like you have some corrosion that the zinc is supposed to prevent.
You may benefit from pulling it out from the engine compartment at this stage and it will be much easier to work on.

CalebD · #7 01-23-2013

As for the frequency for replacing the HX zinc, on my friends Universal diesel (M25 or 5435) the plaque on his HX says: "Inspect zinc monthly". I doubt most casual boaters inspect this zinc more often than yearly, if that, but the instructions to "inspect monthly" are probably more for engines in frequent use. Keep in mind that it is actually a rather small amount of zinc at the end of the bolt. This small zinc protects the fine copper cooling tubes in the HX from electrolysis/corrosion.

As Doug suggests, I found it quite easy to entirely remove the HX from the engine compartment to work on it and replace the zinc. Also make sure you have the right size zinc bolt as they do come in several sizes/flavors. Catalina Direct and West Marine should sell every variety.

Sounds like you figured it out anyway, so good for you.