How often to change Mercathodes?

F

Fish Guts

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8982
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It seems as though my Mercathodes died just about the end of the season. Everything was fine all year, but the last month here I started noticing "white stuff" on my outdrive. Just little spots here and there. I pulled the boat yesterday, and yes, some corrosion on rams and outdrive. Can I wire brush and sand the affected areas and paint, or am I screwed? Mercathodes are just 2 years old, I have the 2 pucks and the one on the bottom of the transom.
Thanks guys...
 
I think we have a mixing of terms here. Mercathode is an impressed current system that is driven by 12 volt power through a controller. You should have either a blue, black or red controller box. You also have sacrificial anodes which act in concert with the Mercathode system. The Mercathode should not "die" and if you suspect it did it is easy to test if it is indeed working or not. The sacrificial anodes should be replaced periodically and realistically should not go beyond one year's use.

So the following questions.

Have you replaced the sacrificial anodes within the past 6 months?

If you have, what is their current condition?

Have you performed a "hull potential" survey?

If you have performed a "hull potential" survey how does the output of the Mercathode compare to those values?

To gain a greater understanding you may want to obtain a copy of a Mercruiser publication, Marine Corrosion Protection Guide" P/N #90-88181301

As to painting an outdrive, see this thread. http://www.boatered.com/forum/topic.asp?TOPIC_ID=97217
 
Please check the inline fuse(s) for the MerCathode. It/they may have blown. they, usually, are inline with a red wire connected to the positive terminal of your battery.
 
Gee Bee, thanks for the reply. I have the black controller. all anodes new at the beginning of this year, and every year, although the fin anode is actually gone now. The mercathodes have worked fine since I put them in. I just think they died this year, not working any more. Never a hull potential survey, didn't think I needed it. Three years ago before I had the mercathodes or isolator, my outdrive basically corroded apart. I replaced the whole transome assembly and outdrive, added the isolator and mercathodes. All was good until the end of this season.

Sugilbert, fuse is good, power going to the controller.

My main question was... How long do the mercathode units actually last? I am replacing them this off season. Question 2 was... If corrosion has started, minimal as it is, can I save the outdrive?

Thanks again.
 
My MerCathodes are going strong after 16 years. Absolutely, your OD's can be saved. GeeBee posted a thorough prep & paint regime several years ago. A search should bring it up.
You didn't, per chance, pressure wash the outer unit(s), did you?
 
It is indeed rare for a controller to go bad. Usually, if you have good power to the unit, it is the reference electrode that goes bad which sends bad info to the unit. Alternatively, it good be a bad output puck. Sometimes you have to install two controllers to get enough output. I cannot strongly enough refer you to the Marine corrosion guide I referenced. If you PM me with your email, I can send you a scanned copy. I also highly recommend you read section 7 of the Mercruiser Bravo service manual which will run you through the test procedure for the Mercathode as well as show you how to do a hull potential check. Every Mercruiser owner who leaves their boat in the water should check their hull potential at least on a quarterly basis. Here is the link to the service manual section 7

http://www.boatfix.com/merc/Servmanl/11/11a7r5x.pdf
 
Do you think the white spots are dried salt...happens on areas that get hot and exposed to the air when running.
 
I installed a second mercathode on both my motors when I had outdrives. I had one mercathode stop working when a inline fuse blew on it.
In the old days they actually had a gauge with a light that showed if the mercathode was working.

GeeBee is the expert in this field. He helped me with my outdrives. Checking my hull potential became a weekly check for me. I also highly recommend the prop zinc if you don't have one. Older outdrives didn't and there is a add-on kit for it.

Make sure your using the right zincs. It's amazing how many people shop price and not the composite material.
 
Thanks for all the input guys... The controller does have a light that says it's working, I guess I meant the electrodes that I think are dead, do they go bad? I didn't have the slightest bit of issue all last season.Charlie, I'm sure it is corrosion, I wish it was salt.Gee Bee, I used your outdrive painting post to do the outdrive on my last boat many years ago,worked beautifully, thanks for that.I have the controller that powers both the gimbal anode and two puck anodes.Having a hard time trying to find just the electrodes without the controller.
 
The light just tells you there is 12 volts supplying the controller, i.e fuse blown. To test the controller correctly you need to apply the procedures in Section 7 of the Mercruiser manual.
 
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