Replacing Engine zincs

Thanks Frank, yep I found the 3rd one. As you said, it's on the opposite end of the heat exchanger, and on the bottom of it so not real obvious.

All of mine definitely needed to be replaced, and I'm going to set a reminder to check them every 6 months to make sure they are good. I'm planning on removing them and taking the zinc out of the cap to prevent them from welding themselves into the cap. Of the 13 zincs I replaced, 7 of them had done that so I had to soak them in the muriatic acid to remove the zinc from the cap. That worked pretty well by the way, so I now have a full set of spares that I can use when I replace the zincs.

Kevin
 
The big difference between the 3116 and 3126 is the aftercooler on the 3126 is raw water cooled and requires 5 (if I remember correctly) zinc's. The aftercooler on the 3116 has engine coolant in it and requires no zinc anodes.
 
General - If the caps are not painted red, take some bright red nail polish and paint the end of the cap - makes them easier to find next time!
 
I just stumbled upon this thread about anodes by accident. Have been boating 30 years with 4 different boats and never even heard of anodes let alone replace one. In fact the topic of anodes has never even come up on the dock with fellow boaters. We boat in fresh water and obviously not a problem here. Am I missing something here or is salt water the problem. I read some people change them twice a year?
 
WOW, that's amazing that you never heard of anodes. Even my dingy has them on the outboard. You can bet your engine HAD them and you should have replaced them. I'm by no means an expert and maybe someone with more knowledge will chime in. I do know that fresh water anodes are made of a different alloy than salt water, and I assume they are of lesser importance than in salt.
 
Yup had one of those boats 13 years no anode change. Wonder how important they really are then?
 
You really don't want to find out how important they are. Anodes are called "sacrificial" for a reason and if the manufacturer thinks they are important protection for some very expensive cast iron, I think that might be a sign.
 
Well I better add that to the to do list this spring. Seems with boating there's always something new to learn
 
Yup had one of those boats 13 years no anode change. Wonder how important they really are then?

Feel fortunate that you're in freshwater. I change my zincs every 3 mos in brackish water


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So after a little research I find that a 3116 has no anodes in the engine or aftercooler. The heat exchanger has 3 the engine and trans oil coolers have 1 each. These have lake water going through them? Fresh lake water. I fail to understand how an anode works here and what they are preventing from happening. Please excuse my question here but I'm just trying to understand what is going on in there. Thanks.
 
Dissimilar metals and alloys have different electrode potentials, and when two or more come into contact in an electrolyte, one metal acts as anode and the other as cathode. The electropotential difference between the dissimilar metals is the driving force for an accelerated attack on the anode member of the galvanic couple. The anode metal dissolves into the electrolyte, and deposit collects on the cathodic metal.

The electrolyte provides a means for ion migration whereby metallic ions move from the anode to the cathode within the electrolyte. This leads to the metal at the anode corroding more quickly than it otherwise would and corrosion at the cathode being inhibited. The presence of an electrolyte and an electrical conducting path between the metals is essential for galvanic corrosion to occur.

In the case of marine engines, we use sacrificial anodes to encourage this type of reaction. The sacrificial anodes work as part of a galvanic couple, promoting corrosion of the anode, while protecting the cathode metal.

You probably saw perfect zincs because you were using zinc anodes not magnesium ones which are for use in freshwater.

Also, the 3116 Caterpillar also has one anode in the exhaust elbow.
 
So I finally got to the boat this weekend and pulled out a couple of anodes. They looked like new or nearly new anyway. Not sure how old they are but at least 3 years as I have not changed them. Is this good or am I missing something here?
 
You are missing something - As FrankW said, if you are using zinc in fresh water, there will be no wear on the anodes. Fresh water forms a coating on the zinc. In fresh water, use magnesium or aluminum anodes...

Here's an article from Cruseing World by Steve D’Antonio:

Aluminum vs. Zinc

ZINC AGAIN: SO YOU THINK YOU KNOW THE DIFFERENCE BETWEEN ZINC AND ALUMINUM SACRIFICIAL ANODES?
BY Steve D' Antonio POSTED March 27, 2014

While commonly referred to simply as “zincs,” sacrificial anodes are in fact available in several different alloys including aluminum, magnesium and zinc, although the latter is the most common. (All anodes contain alloying and trace elements of other metals.) In fact, each metal is best suited to a different environment. Traditionally, fiberglass vessels operating in seawater employ anodes made from a zinc alloy; although ubiquitous, however, they are not necessarily the most desirable option.
Sacrificial anodes are used for one purpose: to prevent or deter corrosion of underwater metals such as propellers, bronze through-hull fittings, and stainless-steel propeller shafts and rudderstocks. (Once again contrary to popular belief, most props are made of a brass alloy such as manganese bronze, which contains zinc and is particularly susceptible to corrosion if not protected by an anode.) Each of these metals should be protected by a sacrificial anode, either directly or indirectly through the vessel’s bonding system.

Regarding galvanic corrosion, each metal possesses its own natural corrosion potential, measured in millivolts: the more “negative” they are, the more prone to corrosion. The goal of the anode, then, is always to be more negative than the metal it’s protecting. The relative energy capacity of zinc is 368 amp hours per pound with a voltage of negative 1,050 millivolts. While that’s adequate in most cases, zinc anodes possess one flaw: When used in brackish or fresh water they are prone to developing a calcareous coating, a whitish material that essentially puts a zinc anode to sleep. Many sailors mistakenly perceive these especially “long-lived” zincs as effective. In reality, they’re anything but; even where anodes are still present, they provide no anodic protection at all. An anode that lasts for an inordinately long time probably isn’t working for any number of reasons, calcareous coating or otherwise.
Aluminum anodes, alternatively, offer several advantages. They’re immune to the calcareous coating menace and are therefore well suited for use in seawater, as well as brackish and fresh water. Aluminum anodes also pack more of a punch; they either last longer than zinc anodes of the same weight, or provide the same protection as zinc in a lighter package. Their relative energy capacity is 1,108 amp hours per pound (significantly more than zinc), with a voltage of negative 1,100 millivolts. If you opt for aluminum anodes, be sure that the change is universal for all anodes used within the same bonding system.
Surprisingly, aluminum anodes are often cost no more than zinc ones. Also, because most are cadmium-free, aluminum anodes are less of a hazard to the marine environment. So, regardless of what a diver, boatyard manager or other industry pro tells you, there are several advantages, and no drawbacks, to switching to aluminum anodes.
As for magnesium anodes, these work in fresh water only. Don’t use them if operating your boat in the briny.
Finally, when purchasing anodes, select those that meet stringent military specification standards: A-24779, A-18001 or A-21412 (for aluminum, zinc and magnesium, respectively). These standards ensure the purity of the alloy, an important factor in an anode’s effectiveness, resistance to self-fouling and longevity. Inexpensive anodes often represent false economy.

_Steve D’Antonio offers services for boat owners and boat buyers through his company, Steve D’Antonio Marine Consulting. This article first appeared in the January 2014 issue of Cruising World.
 
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This is our 5th season with our 340 and we inspect the anodes at the start of each season. Last weekend when we checked there is still about 3/4 left. This got us thinking ... at what point should we be replacing them? Doesn't make sense to replace them when there's still so much left. We looked around at the condition of anodes on other boats ... only to discover all the other boats have anodes on the shafts ... and there never were any on the shafts on our boat. :huh: Definitely going to pick up some and install.
 

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