zinc anode in exhaust mannifold

[KJM]

I was just wondering....I replaced my exhaust manifold on a merc165 l6 about 2 years ago. the old one rusted thru and cracked. the new one was about $1000. I hate to think of that rusting too and wondered if you could drill a hole in the end cap of a manifold and thread a zinc anode inside the cover to stop rust? would it work?

 

[alldodge]

Don't do that, it will not stop the rust. Anodes are used as a sacrificial item for galvanic corrosion. If your in fresh water, the manifolds should last a long time. If your in salt water then not so much

 

[Scott Danforth]

So you replaced your 30-40 year old manifold 2 years ago. You are definitely boating in fresh water.

If you were in salt water you would get 5 years out of a manifold

Your new one will last about the same length of time by then your block will have rusted thru as well.

As AD pointed out, a zinc will not help as this is not galvanic corrosion.

 

[KJM]

Actually i'm in salt water, newfoundland, Canada. however I did buy the boat about 3 years ago and the prev owner said it was from the great lakes so most of life fresh water. so in salt water it will only last about 5 years? I guess that's if its left in water all season, I tow mine and clean with fresh after each weekend. just the same I don't get why the anodes wouldn't help. they would provide the sacrificial ions instead of the metal in the manifold.

 

[alldodge]

The manifolds are not as anodic then other metals on the motor. In short the aluminum drive will fail before the manifolds do to galvanic corrosion. In the table below note that cast iron on the left side come into being more anodic when placed to stainless. The aluminum is far more attracted (so to speak) then the other metals.

If you flush your motor regularly it will last longer. The 5 years is the norm, but many have made it to the 7 and 8th years, but 8 is pushing it without doing flushing

 

[Scott Danforth]

With flushing you can get about 10 years

 

[KJM]

ok thanks for the info. I guess i'll keep flushing and hope for the best. is there anyway to check their condition as they get older?

 

[alldodge]

ok thanks for the info. I guess i'll keep flushing and hope for the best. is there anyway to check their condition as they get older?

Only way I know is inspection. Need to remove the riser and see how their looking every couple years or so, or in your case the end caps