Engine anode failure?

This zinc anode was in-service exactly 12 months. Look how it was chewed off at the base but the anode looks mostly intact. This is a Perkins 4.236. I would hope it would have wore down all over.

In my experience, the anode will break off early about 50% of the time. If your replacement schedule is annually, that will leave you without protection for most of the coming year. Add to that the restriction of water flow in the HE from the big lump of zinc and you wonder why they bother with an anode at that location. I have pulled my HEs (on several engines) apart to clean them out and never seen any evidence of electrolysis, so the lack of an engine zinc periodically hasn't made a huge impact.

Greetings,
Mr. k. "never seen any evidence of electrolysis" Could it be that the wayward stub of the zinc is still in electrical contact with the body of the HE thus providing protection?
A problem I've run into the last couple of zinc service sessions is I've been unable to buy replacement zincs with the same threads as the existing brass plug. Likewise, my local zinc source does not have the replacements with the brass plug. "Nude" zincs only. My solution has been to re-tap the brass plugs. VERY easy. Same diameter, different TPI.

I have the stbd engine and generator to do next but if the rest look like this I might try a spring-fall schedule. My boat in in the water all winter.

Mr. RT I think I will try the drill and tap next time. the anode without the brass is 1/2 the price.

RT Firefly said:

Greetings,
Mr. k. "never seen any evidence of electrolysis" Could it be that the wayward stub of the zinc is still in electrical contact with the body of the HE thus providing protection?
A problem I've run into the last couple of zinc service sessions is I've been unable to buy replacement zincs with the same threads as the existing brass plug. Likewise, my local zinc source does not have the replacements with the brass plug. "Nude" zincs only. My solution has been to re-tap the brass plugs. VERY easy. Same diameter, different TPI.

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Greetings,
Mr. 36. I don't even remember drilling other than to get the remains of the zinc out of the brass plug. As I said, the diameter of the threaded recess in the plug is the same just the # of threads per inch is different. You're basically ruining the existing thread by cross threading with the tap BUT it dies appear to work. Could be the existing thread was 1/4-28 and I simply bastardized it with a 1/4-20 tap or vice-a-versa. Come to think of it I may have re-threaded the zinc instead. Good Grief!!! Don't ever get old. The memory isn't the FIRST to go....I also may have soaked the brass in something to dissolve the zinc???.....OK. I'll give up now.

Yanmar brass zinc heads have a slightly different thread on the OD of the brass plug- BSP vs NPT and a very different thread on the zinc. The brass plug OD thread is close enough that I just buy new NPT brass plugs, screw them in and from that point forward I can use NPT pencil zincs.

David

Long story short: I burned through two heat exchangers at $700 a pop on my old Onan generator before an educated tech figured out it really DID need an engine zinc and that it had the wrong heat exchanger case on it. So we ordered a new case that accommodates a zinc and wow those heat exchangers on Onans really can last a long time rather than the measly two or three thousand hours we were getting before!!

RTF:
If the wayward stub was doing anything, it would be reduced in size. Mostly I see lumps that are not much reduced in size, just broken off.

Gulfstar 36 said:

This zinc anode was in-service exactly 12 months. Look how it was chewed off at the base but the anode looks mostly intact. This is a Perkins 4.236. I would hope it would have wore down all over.

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What is chewing the anode off? I too would have expected it to disolve fairly evenly.

Greetings,
Mr. k. Good point.

rwidman said:

What is chewing the anode off?

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Maybe this with carbide teeth?

Onan 4 kw Generator Zinc

My 4 kw Onan generator is located aft in the engine room & sufficient access to the heat exchanger side is not possible. i can only quess the addition of an aftermarket Sen-Dure remote unit will be the recommended fix. Any other ideas?
Jim M/V Mello Moon

A couple things for you guys:

You can just cover the the bronze plugs with muratic acid in a small container and in a minute or two the zinc is gone and the plug is ready for a new zinc.

Galvanic activity is like a plating process. Realize that the zinc anode is sacrificing into the seawater to be deposited on the bronze internals. This zinc is keeping your bronze internals from sacrificing some other less active metal such as an exchanger housing material that has made contact with the bronze through the sea water somehow.

Gulfstar 36 said:

This zinc anode was in-service exactly 12 months. Look how it was chewed off at the base but the anode looks mostly intact. This is a Perkins 4.236. I would hope it would have wore down all over.

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The anodes in my Perkins 6.354's heat exchangers only last about six months. Any longer and you get the results you are getting. You're protecting the bronze tubes in the heat exchanger on the saltwater side and not the fresh water (coolant) filled cast iron engine block. That's why there is no zinc in the engine block.

I cast my own zinc's and change them out twice a year. In the case where one breaks off, I melt it out of the bronze cap with a propane torch. When heating the cap, face the zinc side of the cap toward the ground or away from you in case there is any water under the zinc which may cause it to pop molten zinc when super heated.

I have found that the zinc on my port engine lasts 2 times as long as on the port. I have added the stbd zinc to a 5 month check and replace.

Check them every three months. If they are starting to go, they will unthread easily and no damage to the expensive parts.

You may have a little stray current running around on that one engine...give it a good cleaning, replace all terminal blocks and wire ends,,,

Before all that I guess you could disconnect all grounds and see if there's any current between the block and a ground wire....

If I left the same zincs in my genset for a year, it would not start. That's because the sound shield would be empty!

I don't think I have ever had a zinc corrode evenly. Sometimes more evenly than other times but never evenly. Often if they are actually poked at when out a lot of metal will simply flake or slough off. It has done its job, just hasn't fallen away yet.

If you are leaving your engine zincs for a year that is far too long.

You should be checking them far more often, more likely every 2-3 months.
If they are ok then change them regardless but lengthen the interval a bit. When they look like they are half gone , it is definitely change time., but they may need to be poked or brushed a bit to really see how much is left.

But don;t just leave them, ever, with some predetermined idea of how long they will last.

Just in case you are thinking that the big hull mounted zinc will help, then NO, it won't. The engine , gear and any other internal equipment zincs are protecting closed, almost totally isolated systems, that have different requirments than the external metals.

Pencil zincs with steel threads?

The zincs on our Gulfstar 43 (Perkins 6.354's) when we bought it had steel threads, so that when the rest of the zinc corroded away, you could easily screw them out with a pair of pliers. But I'll be danged if I can find replacement zincs with the steel threads. Anyone know where to get these?

Alternatively, I do like the idea of using muratic acid to eat away the remainder of the zinc threads - is it really that easy? (Not as fond of using heat, although that seems viable, too.)

I just hate having to buy the new brass base every time I need to replace the zincs.

BTW - on our engines (1974 vintage), we have to cut the 2" zincs down by 1/4", or they hit something inside the HE and break off. Took me several zincs and lots of head scratching to figure that one out!

New brass is a good idea as pipe threads are designed to distort with tightening. Single use type stuff. If there is no old junk inside cutting off the zinc is common.


Muriatic does dissolve the zinc and clean up the brass but unless you plan to run a die over the plug to recut the threads, which will further set the zinc into the cooler.. why bother


If you don't wait until there is nothing left you should be able to unscrew the zinc easily.

Should take a 2" zinc. Did you open the Heat exchanger, take the end cap off, to see what's going on. Could be part of the broken off zinc laying in the bottom or maybe it's an aftermarket heat exchanger with different dimensions??

I've never seen the "steel" threaded zincs.

The best way I've found to remove the broken off stub is with a propane torch and an old cast iron skillet. Be sure and hold the cap with a pair of pliers facing zinc side down in the pan away from you. Heat the back of the cap until its hot and it begins to smoke, tap the bronze cap in the bottom of the pan and the melted zinc will fall out. You can use a thread chaser to clean up the threads and remove any left over zinc. I usually do 4 or 5 at a time to make it worth my time.

Be sure and do this in a well ventilated place, preferably outside and wear some eye protection and leather work gloves.

Interesting thread on zincs. My new to me boat (1990 marine trader) has 2 Perkins 6.354's and I was told there were not any engine zincs to change. Could this be correct?? If there are zincs, where would they be located??
Thanks!

mike_nickens1 said:

Interesting thread on zincs. My new to me boat (1990 marine trader) has 2 Perkins 6.354's and I was told there were not any engine zincs to change. Could this be correct?? If there are zincs, where would they be located??
Thanks!

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Very True. . .given the year of your boat I would assume you have Perkins 6.354-4 (Range 4) engines. If so, you probably have a manicooler instead of separate exhaust manifold and heat exchanger. You would have to confirm that though to be sure. I do not know if the manicooler had zinc pencils or not. Maybe someone else with Range 4's will respond.

Perkins did not install zinc's in their engine blocks, they're fresh water cooled and not necessary. The only zinc was a pencil zinc in the heat exchangers. Not even the original combination oil cooler had zinc. Mine are 1976 6.354-M, same basic engines, but different HE. The only zinc is in the heat exchangers and the aftermarket (replacement) oil coolers have pencil zinc.

If you change the zincs before they all but disappear, you can unscrew what is left most of the time. For every 20 zincs with brass tops I buy, one or two have to be tossed and the rest I just screw a new zinc in.

Thanks for the reply Edelweiss. Yes, my engines are range 4's with the manicoolers, so I guess I don't have to worry about zincs!
Thanks again!

bayview said:

Muriatic does dissolve the zinc and clean up the brass but unless you plan to run a die over the plug to recut the threads, which will further set the zinc into the cooler.. why bother

If you don't wait until there is nothing left you should be able to unscrew the zinc easily.

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I finally got around to buying some muratic acid (it's labeled hydrochloric acid, but the guy at the pool supplies store says it's the same thing - Google seems to concur). Plopped one of those brass plugs in, and man, did it go to town on the zinc that remained in the plug! I now have three clean brass plugs, ready for the cheap screw-in pencil zincs. (As for recutting the threads, bayview - I think I'll take my chances that they'll still seal just fine without that. I don't think there's all that much pressure building up in the heat exchanger.)

Just a little warning - putting zinc in acid produces hydrogen gas, lots of it. It's how we used to make "UFOs" when we were kids. Hold a dry cleaning bag over the reaction vessel and fill it with hydrogen, seal the bottom and let go. Extremely explosive! Be careful!

Xsbank said:

Just a little warning - putting zinc in acid produces hydrogen gas, lots of it. It's how we used to make "UFOs" when we were kids. Hold a dry cleaning bag over the reaction vessel and fill it with hydrogen, seal the bottom and let go. Extremely explosive! Be careful!

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So if I filled a really BIG bag with it, it could lift me up? ("Oh, the humanity!")

Thanks for the warning. The smell, and the feel in my nose, of the first whiff told me to stay the heck away from it, but I didn't think about it being explosive. Next time, I'll do it outside instead of in the kitchen.