posted 07-21-2009 02:15 PM ET (US)        

Just curious what everyone would choose if you had to replace the anodes on your Merc outboard.
For strictly saltwater use, would you choose Mercury's aluminum alloy anode OR would you go for regular zinc? If zincs are less noble than aluminum, wouldn't the better choice be the zinc?

Rust and crevice corrosion is starting up on my 2001 Optimax motor. The anodes are the original ones so I want to replace them. Just not sure if I should go OEM or replace with pure zinc.

posted 07-21-2009 02:42 PM ET (US)            

I would go OEM....especially in fresh water. But in Salt - you will replace anodes faster than if you used zinc. Who cares - the reason they're called sacrificial anodes is because they are designed to be used up and replaced. Buy the OEM.

posted 07-21-2009 03:08 PM ET (US)            

You can buy Canada Metals anodes at your local chandlery. They look just the same but they are not the same mixture of alloys.

posted 07-21-2009 03:55 PM ET (US)            

And as K Albus noted, this is what West Marine says about anodes:
"If you are a saltwater boater, you should install zinc anodes to prevent galvanic corrosion on the engine and underwater parts of your boat. Look for aluminum anodes as a possible replacement because they last longer while providing the same level of protection as zinc."

My interpretation is WM is first recommending zinc for saltwater boaters for optimal protection. Then aluminum as an alternative if you want something that last longer and almost as good as zinc. Price wise, the aluminum anodes cost more than zinc anodes manufactured by Canada Metals offered at West Marine.

Now the skeptical side of me wonders how can Merc sell an aluminum/zinc anode which is cheaper, better, AND last longer than plain zinc? Sounds too good to be true. And all the old salts I have talked to says to use proven zinc for saltwater boating.

posted 07-21-2009 07:46 PM ET (US)            

"...the aluminum anodes cost more than zinc anodes manufactured by Canada Metals offered at West Marine"

"...how can Merc sell an aluminum/zinc anode which is cheaper, better, AND last longer than plain zinc?"

There seems to be some contradiction there. Can you explain?

posted 07-21-2009 08:23 PM ET (US)            

I was comparing 3 anodes offered at West Marine. There are actually 4 but I'm not considering the one made of magnesium. Looking at the West Marine list prices for the wedge pocket anode, here's what they cost.
First time I see I Merc part cost less than non-OE!

MFG Part#
CM826134KITA Aluminum anode kit by Canada Metals $29.99 (~$15 each)
CM826134Z Zinc anode by Canada Metals $13.99 each
826134Q Aluminum/Zinc anode by Mercury Marine $8.79 each

I speculate Mercury's motivation to come up with a aluminum/zinc alloy is to streamline parts inventory. And while they had such a product, why not patent it. Its much more cost effective for them to offer a single general-purpose anode where they can slap it on every outboard they sell and not worry about whether the customer will be using the motor in fresh, brackish, or saltwater. This is why I'm leaning towards a regular zinc anode as my replacement.

posted 07-21-2009 11:01 PM ET (US)            

"Remember, whatever anodes you choose to use, use the same type on all locations. You do not want to mix different types of anodes because the least noble will do all the 'work.'"

posted 07-22-2009 12:52 AM ET (US)         

In Mercury's advertizing literature, they claim to have the exclusive rights to this alloy, as for years the other manufacturers only had access to zinc. Who owns the Patent, I don't know. Maybe Mercury, and Canada makes them for them, maybe Canada and Merc bought the exclusive rights.

posted 07-22-2009 06:50 AM ET (US)            

The problem with galvanic corrosion is influenced by the mount of other metals in the water. If you have a large stainless steel propeller you may need more protection than if you have an aluminum propeller. Mercury also found that use of stainless steel for some internal components of the gear case was causing problems and necessitated special sacrificial anodes to be installed to suppress galvanic corrosion.

One consideration in providing protection against galvanic corrosion is controlling the voltage potential that exists between the metals. It may be possible to provide too much protection by creating too much voltage potential between most noble and least noble metals, and by having too much surface area.

It makes perfect sense to me to use the manufacturer's recommended anodes. We are talking about a miniscule cost difference among OEM and non-OEM anodes (and apparently not even a savings) compared to the replacement cost or repair cost of the engine, and it is unlikely that there is much advantage to be gained by using non-OEM brands. This is particularly true during the period when an engine is covered under warranty against corrosion. I suspect that if non-OEM sacrificial anodes were used to replace the OEM sacrificial anodes, the manufacturer might have reason to deny warranty coverage, and probably rightfully so.

posted 07-22-2009 03:01 PM ET (US)            

It would probably confuse their readers if they included a blurb about a 4th type of anode made of an aluminum/zinc alloy sold by Mercury and only available for Mercury engines. And this is exactly what I'm trying to figure out here. What application is best for this 4th type of anode.

Current state of anodes on my 2001 Optimax. Operated in saltwater only. Rinsed after each use and boat sits on a trailer. These are the original ones that came with the new motors.

http://home.sanbrunocable.com/~ivanlum101/boat/anode1.JPG
http://home.sanbrunocable.com/~ivanlum101/boat/anode2.JPG

posted 08-05-2009 08:33 PM ET (US)            

After removing the old Merc anodes, I found there to be much corrosion at the bolt holes and areas where the anodes make contact to the motor. So much that I believe they were not making a good electrical contact rendering them useless. And the old anodes weigh only a fraction of the new zinc anodes. The difference in weight can be attributed to aluminum vs zinc but I think also a lot of the weight was gone due to wear.

So those with anodes over 5 years old, you might want to pull them off for inspection. I'm glad I did the swap out.

posted 08-05-2009 08:55 PM ET (US)         

You state your Mercury Optimax has had the original Mercury anodes on it for six years, and say:

"Afterall my motors have been more or less corrosion free for the first 6 years of ownership."

Then you switch to less protective aftermarket (old fashioned, old technology) zinc anodes? It seems to me "if it ain't broke, don't fix it" The reason your saltwater use engine has been totally corrosion free is, first of all, the high quality aluminum alloy and EDP paint system Mercury uses, and secondly, the exclusive Mercury aluminum anodes.

The reason your original anodes look pretty eaten up is that is exactly what you want. I have a pair of 1984 Merc 115's, and a 1988 150, both of which were manufactured before the aluminum anodes were invented, and came from the factory with the old style zinc anodes. They barely sacrificed at all, hence giving little protection. When I upgraded to the new style, protection greatly increased in salt water and freshwater use, and they look like yours do after a few years. Incidentally, Mercury says to replace anodes when they are 50% consumed.

posted 08-06-2009 02:13 AM ET (US)            

I went with zinc because I want the least noble anode for my motors. According to metal charts I've seen, zinc is less noble than aluminum. I am counting on the zincs wearing out even fast than the original anodes. That's fine with me because I want the best protection and will to sacrifice some longevity. The Merc aluminum anodes may last longer but there is no evidence the Merc anodes offer more protection than zinc. I think they are just made to last longer and claim to be as good as zinc.

Though the Merc anodes worked fine for the first 4-5 years, I feel they did FAIL on me because my motors are showing signs of rust. If my motors were rust free, I may have more faith in Merc's anodes. So now I'm going to follow the advice of old salts and see how the zincs work out.

posted 08-06-2009 02:13 AM ET (US)            

I went with zinc because I want the least noble anode for my motors. According to metal charts I've seen, zinc is less noble than aluminum. I am counting on the zincs wearing out even fast than the original anodes. That's fine with me because I want the best protection and will to sacrifice some longevity. The Merc aluminum anodes may last longer but there is no evidence the Merc anodes offer more protection than zinc. I think they are just made to last longer and claim to be as good as zinc.

Though the Merc anodes worked fine for the first 4-5 years, I feel they did FAIL on me because my motors are showing signs of rust. If my motors were rust free, I may have more faith in Merc's anodes. So now I'm going to follow the advice of old salts and see how the zincs work out.

posted 08-06-2009 04:25 PM ET (US)         

One season in FL, I had a West Marine "heavy" zinc trim tab on one engine, and a Merc "lightweight" trim tab on the other. After 6 mo in FL. the Merc anode was badly pitted and eroded, and the zinc one showed no erosion at all.

I have tried magnesium anodes in Freshwater only use, as recommended, and they also do not sacrifice as fast as the Mercury anodes do. Don't ask me why. I'm just giving you first hand information from extensive use of all three types, over 40 years of owning Mercury outobards.

I understand that Yamaha has also switched to some lightweight alloy for its anodes.

posted 08-06-2009 10:29 PM ET (US)            

http://www.ceoe.udel.edu/seagrant/publications/corrosion.html

in which the author says, without reservation, regarding protecting other metals, that:

posted 08-07-2009 06:19 PM ET (US)            

I don't have any problem with using the OEM anode on a Mercury, but I need someone to explain to me:

--why I would want to use a Mercury anode on another brand, or

--why a Mercury anode is supposed to be superior to other OEM anodes, or

--why use of Zinc would be inferior to a Mercury anode on an electro-chemical basis. I don't need the marketing hype, just the electro-chemistry that makes Mercury better.

posted 08-08-2009 09:07 AM ET (US)            

quote:

---

Mercury's aluminum alloy anodes came out in 1991, I believe, and Mercury claims them to be 50% more effective in controling galvanic action than the old fashioned zinc.

---

Larry,

That was about the same time that OMC started using aluminum anodes, too. I don't remember the exact year, though.

OMC said the same thing as Merc, the pure aluminum alloy protects better than the traditional zinc products. Part of the reason is the amount of contaminants in the zinc castings and smelting procedures compared to quick and cheap ceramic die-casting of the aluminum.

Gearcases and other aluminum cast engine parts are special alloys with traces of other metals for strength, machining ease, and other properties such as corrosion resistance. The anodes are a pure alloy that is less noble so it will sacrifice itself first.