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Thread: Rusted exhaust manifolds
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11-05-2010, 10:19 PM #1Junior Member
- Join Date
- Oct 2010
- Location
- Tucson, Az
- Posts
- 18
Rusted exhaust manifolds
I was poking around my engine today and noticed that the exhaust manifolds have really bad rust/flaking on the bottoms. There are some thick chunks coming off them. It is a 98 and I'm sure that they have never been touched but should I worry about this and spend the money to replace them? Something is obviously leaking but I'm new to the boat so I don't know how bad or if some leaking is normal. Any thoughts?
1998 Outback
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11-05-2010, 10:52 PM #2
It's normal for rust to develop on inboard manifolds. It does get worse if not maintained each year. Unless they are leaking I wouldn't worry about. What does interest me is the fact it's doing that in such a dry climate as Arizona. Anyway, get a stiff wire brush and scour them clean then paint them up. Quicksilver makes a great paint made for Mecruiser that's super heavy when dry and protects well. Or just use a good exhaust manifold paint.
2007 Mobius LSV
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11-05-2010, 11:10 PM #3Senior Member
- Join Date
- Jan 2008
- Location
- Pensacola, FL
- Posts
- 1,585
Rust is oxidation, which is a heating process (exothermic). The exhaust manifold at the bottom as it bends upward is one of the hottest places on the engine/exhaust. This, along with moisture, promotes rust specifically in that area. It is 'normal' and every inboard will do it.
I use a wire brush and knock off as much as I can and then hit is with some black paint from a spray can. Do it each year when you winterize and your manifold will last a long time and look good too. Those things are quite thick, so you should not need to replace it. However, it's tough to say without seeing.1997 MasterCraft 205
2008 Moomba Outback
1999 MasterCraft Sportstar OB
1992 MasterCraft 205
1999 Malibu Response LX
1987 Marlin Magnum Skier