Aluminum Zincs?

[robbyusa]

Since Mercruiser stern drives come with aluminum Zincs should they be replaced with aluminum anodes when the time comes in salt water? Are zinc anodes cheaper or better?

 

[jim dozier]

Re: Aluminum Zincs?

I don't think they come with aluminum sacrificial anodes. They might be magnesium or zinc. Aluminum anodes aren't going to protect aluminum (engine and outdrive) cathodes.

 

[ED21]

Re: Aluminum Zincs?

I read an article recently that mercruiser zincs should only be replaced w/ mercruiser factory zincs. <br />Something about the formulation is different than aftermarket zincs.<br />The aftermarkets don't work well in this case.

 

[18rabbit]

Re: Aluminum Zincs?

The galvanic process is electrical and has nothing to do with the manufacturer, but everything to do with the molecular composition of the sacrificial anode. The greater the difference in the voltage of the corrosive potentials, the better the protection. From Calder’s “Manual” here are the voltage potentials for the metals in discussion:<br /><br />Magnesium (with or without alloy) –1.00v to –1.63v. <br />Zinc –0.98v to –1.03v.<br />Aluminum alloy –0.76v to –1.00v<br /><br />For the greatest protection, you want the metal you are protecting to be as far into a positive number as possible and the sacrificial metal as far into a neg number as possible. If Merc is using an aluminum alloy with a corrosive potential of –1.00v, using a zinc with a potential of –0.98 will cause the two metals to reveres rolls…the stern drive may become the sacrificial anode that protects the zinc. I don’t know but I speculate Merc’s own anodes are magnesium based with a corrosive potential lower than –1.00v.<br /><br />Note: what’s not taken into account with the above numbers is the ‘active’ potential of the metals. As a current is applied to a metal it’s corrosive potential can increase.<br /><br />I wouldn’t mess with it. I’d go with Merc’s own anodes. Hope that helps.

 

[robbyusa]

Re: Aluminum Zincs?

This seems to be one of those times that the charts and books everyone makes there choices by are not sophisticated enough to keep up with what really works. I posted a question about antiseize a week or so ago and got all the same chart and book answers but never got a real world example of why antiseize is so bad especially since it works so good. <br />Beleive it or not aluminum anodes are recommended on mercruiser outdrives. <br /> I just posted to find out why people are not using them.

 

[Scaaty]

Re: Aluminum Zincs?

Just use what they recommend. They designed the Mercathode system for a reason

 

[robbyusa]

Re: Aluminum Zincs?

Actually I am not refering to the mercathode system. <br />All mercruiser stern drives come stock with aluminum anodes whether equiped with the mercathode system or not. <br />Just a clarification.

 

[rodbolt]

Re: Aluminum Zincs?

the aluminium anodes are a special alloy that merc decided to use. magnisium alloys are for freshwater protection. the zinc alloy is still avalible. as far as the anti-sieze question as long as the mix is a tin/nickel and not copper its ok for marine use. but I have seen copper here in the salt pond eat aluminum housings. you should see what copper anti-fouling paint does on a gearcase here in the salt pond. I have seen it eat dime sized holes right into the oil area . good luck and go with what the factory service/owners manual says.