magnesium pencil anodes for diesel 3116

mtnandy

Member
Nov 24, 2008
125
Smith Mountain Lake VA.
Boat Info
400da sundancer
Engines
Cat 3116 Diesel
I have discovered that we are supposed to be using magnesium anodes in fresh water because the zinc anodes wont work ( will not react to fresh water and sacrifice ) So I have looked to find the magnesium pencil anodes that I need for my cat 3116 engines and have been unable to find the correct size and or the correct brass plug.. I have new zinc anodes and plugs that I just bought but if they won't sacrifice and protect, there is no need to put them in . Does anyone know where I can get the magnesium anodes I need ?
 
Zinc will still work in Fresh water. Magnesium is higher on the galvanic scale than zinc however. Read the attached information on Galvanic Scale.
http://corrosion-doctors.org/Definitions/galvanic-series.htm
Essentially the higher an element is on the galvanic scale, the more readily it will sacrifice itself for elements below it. Both Zinc and mag are well above steel.


Apparently zinc in freAsh water forms a film over it and then the reaction stops. That is why zinc last forever in fresh water.
 
I do not know where you can get the magnesium pencil anodes, you might try boatzincs.com, but they suggest I use aluminum hull and tab anodes and zinc on the engine, aftercoolers. Maybe because they don’t sell aluminum pencils J When I called them a few weeks ago to talk about transitioning into and back out of salt this coming year, they said to stay with the aluminum but to replace the zinc pencils when going into the salt because of the coating that renders them useless that you mentioned.
 
I do not know where you can get the magnesium pencil anodes, you might try boatzincs.com, but they suggest I use aluminum hull and tab anodes and zinc on the engine, aftercoolers. Maybe because they don’t sell aluminum pencils J When I called them a few weeks ago to talk about transitioning into and back out of salt this coming year, they said to stay with the aluminum but to replace the zinc pencils when going into the salt because of the coating that renders them useless that you mentioned.


Yep I tried "Boatzincs.com" and they don't offer the magnesium pencil for the Cat engines. So since the zinc gets a coating and does not sacrifice when use in fresh water, and I can't find the magnesium ones I need , I guess I will just not bother to put the zincs in. I bought the boat about 1 1/2 yrs ago and my guess is that the pencil anodes have not been changed since the boat was put in fresh water 17 yrs ago.
 
You are going to need to most likely have your aftercoolers and heat exchangers removed and cleaned if the pencil zincs have never been changed. If you removed two adjacent aftercooler zincs, shine a pen light in one while looking into the other to see how much corrosion is in it.
 
Yep I tried "Boatzincs.com" and they don't offer the magnesium pencil for the Cat engines. So since the zinc gets a coating and does not sacrifice when use in fresh water, and I can't find the magnesium ones I need , I guess I will just not bother to put the zincs in. I bought the boat about 1 1/2 yrs ago and my guess is that the pencil anodes have not been changed since the boat was put in fresh water 17 yrs ago.

I know for fact that the PO of my boat never changed the zinc anodes anywhere. Practically no one does here because they will last forever, but they do need to be changed (or cleaned) in order to work. I put new zinc pencils in when I bought the boat and remove them in the spring each year and clean them, then reinstall, believing the zinc is better than nothing. Boazincs said that the 2 different materials (aluminum hull and tabs and zinc pencils) won't be a problem.
 
I know for fact that the PO of my boat never changed the zinc anodes anywhere. Practically no one does here because they will last forever, but they do need to be changed (or cleaned) in order to work. I put new zinc pencils in when I bought the boat and remove them in the spring each year and clean them, then reinstall, believing the zinc is better than nothing. Boazincs said that the 2 different materials (aluminum hull and tabs and zinc pencils) won't be a problem.
How do you clean them?
 
So just how difficult would it be to make our own. We could remove the zinc from the brass plug and melt down some magnesium and pour it into a form that sits on top of the brass plug.
 
Home casting magnesium is far fetched. However, machining magnesium anodes is quite easy. About 10 years ago I bought some magnesium rod from a zinc company (rotometals, inc. ) and made several anodes for a friend's 3116 that he kept on a lake in Chattanooga.
 
Andy - did you compare the magnesium andodes that boatzincs.com offers and see if you can substitute any of them? They might be 1 1/2" instead of 2 1/2", but they may work... Like using an E-1M for an E-0A...
 
Home casting magnesium is far fetched. However, machining magnesium anodes is quite easy. About 10 years ago I bought some magnesium rod from a zinc company (rotometals, inc. ) and made several anodes for a friend's 3116 that he kept on a lake in Chattanooga.

Sounds like a possible retirement "hobby" Frank!
 
Nope………….I don't have the time or inclination to accept more liability, but I would be happy to talk you thru the process. I also suspect Dale Dupuis might make anodes if you asked him since he does have a machining business on the side.
 
I'm too gunshy about the flammibility of magnesium flakes and dust - we had a magnesium gearcase fire on a Pratt 2037 on a 757 years ago and it was not easy for the CFR team to put out...
 
I watched a couple small magnesium castings go up in flames some years back - quite a show! By the way, that's not a fire you want to throw any water at....

With regard to making up some custom magnesium anodes, send me a PM, and we'll discuss it. They're pretty simple to machine from round stock.

Dale
 
Dale,

Take a look at the Rotometals site. Their magnesium rods are an alloy that is something like 95% magnesium and comes in lots of diameters. When I made the anodes, all that was necessary was necking down the end to thread diameter and threading the end. I had no problems but I wasn't in a hurry, ran the lathe slow and took light cuts to reduce heat. The down side is that going slow burns up a lot of time and makes the anodes expensive if you do this as a paid service for others.
 
I'll sit down with Andy's chart (someday - unless you already have Andy) from Performance Metals and try to cross ref them with our sizes...
 

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