Fresh Water Anodes?

K

Karl

New member
My understanding is that for fresh-water use, magnesium anodes are the appropriate ones to use, rather than zinc or aluminum.

My understanding also is that the major outboard motor manufacturers currently equip their motors with aluminum anodes...both on the lower unit and for the internal engine ones in the cooling system.

Are mixed anode materials a problem? In my case, would it be appropriate (or, necessary) to swap-out the internal ones for magnesium, or, for people who boat in salt doing this to replace them with zinc.

I'm guessing that mixed materials are OK, and that the internal aluminum ones are OEM as a compromise for fresh/salt.

Even studying the FAQs on the two major anode-supplier websites does not seem to address this point. Do I worry too much?
 
Anodes are sacrificial to protect the outboard metal parts and most important item is to inspect them on a regular basis and replace when they are 50% depleted. My conundrum is knowing the quality of the metal used and where it was made.
 
never thought about the material they are made of...always thought they were zink... I replaced mine after 8 years ... motors never left in the water more than needed....and most of the time on a trailer... they were not 50% yet....maybe 40% gone...it was just a good time to do it while I was doing the major service...carb rebuild etc. Did not cost much...and now they are perfect.

Joel
SEA3PO
 
I've asked local outboard mechanics here in Redding about the Zinc/Aluminum/Magnesium differences for fresh and salt water and they just give me the "what planet are you from?" stare back, then usually say it doesn't make any difference, as though they're trying to convince you they know what they're talking about! (?)

Since the zinc anodes or anything else on my motor don't ever corrode, I guess I'm doing OK, and the correct answer, whatever it is, is therefore moot. (?)

What, me worry?
mad_magazine_guy_-_alfred_e_bush.gifmid.gif

Why should you?

Joe. :teeth :thup
 
There is a good and simple article at:
http://gulffishing.com/tips_anode.html By two experts.

Generally for the majority of C Dories aluminum anodes would be appropriate for the engine. Fresh water magnesium is better in some circumstances--but should not be used in Salt water.

I boat in brackish to fresh water, with excursions to salt water--and aluminum are the best. They are rarely "used". I do have a silver chloride cell electrode, and have used it to check my boats, and degree of protection.

Here is a "course" in corrosion and electrolysis:
http://corrosion-doctors.org/Principles/Course.htm Page 7 of module 4 is on silver chloride reference cells. But you may need to bone up on basic chemistry and physics for this course....
 
thataway":3lognpbv said:
There is a good and simple article at:
http://gulffishing.com/tips_anode.html By two experts.

....
Click to expand...

Their conclusion seems to be that aluminum anodes are the way to go, with zinc maybe not giving enough protection and magnesium giving over-protection...too much of a good thing in certain waters.

When I first started snooping on this subject, I was totally confused about how an aluminum anode could be sacrificial to an aluminum outboard...

But it seems that "aluminum" is not the same thing as "aluminum" in this case. The anodes are a galvanically lower, more corrosive aluminum than is used in lower units...looks like the anodes may be a pure aluminum whereas outdrives are alloyed with other additives which make them more noble than pure aluminum.

I wonder if anodes are now China-sourced, though...their metallurgy
is always suspect.
 
rogerbum":pbcuipm0 said:
Karl - it's simple - just buy a Chinese outboard and use that to protect the others.... :wink:
Click to expand...

OH MAN, Roger, now some of us ar going to need to run triples :P

Harvey
SleepyC :moon

IMGP1255.highlight.jpg
 
The fresh water anode will be eaten fast in salt water. You want only one type of protection. It is quite possible that there will be reaction between the two types of electrode metal--with one being more noble than one.
 
From my readings, it appears that mixed anodes end up causing one anode to protect another anode rather than protecting stuff attached to the boat.

Aluminum anodes seem to be the best compromise for all types of water.
Plus, aluminum anodes are what are used by virtually every outboard and I/O manufacturer, including internal anodes protecting the cooling system.
 
A lot of us have Honda outboards. So where is a good place to buy aluminum and/or magnesium anodes?

A lot of places have zinc, and indeed that's what came with the Honda, and that's what Honda recommends (or at least sells.).

Boris
 
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