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zinc oxide plugs in aluminum exhaust manifold


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I have a 2007 malibu 247 RX. One of the zinc plugs in the aluminum exhaust manifold blew out. How do I fix this? Also why do they have the plugs? Is it like a freeze plug. If so what should I be looking for that caused the plug to blow out? My exhaust manifold is polished aluminum. The ones I see online are black. Any difference in the two other than color?

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1 hour ago, BeRad said:

I have a 2007 malibu 247 RX. One of the zinc plugs in the aluminum exhaust manifold blew out. How do I fix this? Also why do they have the plugs? Is it like a freeze plug. If so what should I be looking for that caused the plug to blow out? My exhaust manifold is polished aluminum. The ones I see online are black. Any difference in the two other than color?

The zinc plug is a sacrificial anode.  It slowly degrades due to electrolytic action as water moves through.  I hear that it is possible to weld new ones back in.  I am pretty sure that my buddy just welded aluminum plugs in and forgot about the zinc.

Another option is to sell your old manifolds to me and get new ones....

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Well I can't seem to find new ones. The only ones I found were for the smaller motor. They were black and cost about $850.00 a piece. So I think I will get these ones fixed. I have less than 200 hours on the boat so I was pretty surprised that they failed. Could there be something else that caused them to get to hot or is it just the slow degrade you said above? What is the point to them?

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  • 2 weeks later...

It's a casting port that's used in making of exhaust manafold, it is a welded aluminum plug.  Cheep way is to clean up the area and use JB weld, or have the port welded over.

Here is a pic of blank plugs from indamar to use to to weld over the port.

0614201755_HDR.thumb.jpg.b8498ec3dfedd8d9c75e47ef0ee32321.jpg

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