Too much rust on exhaust manifold?


Hey guys, I have a 2005 Honda Civic VP (same as LX) with around 115k. It’s my go to work vehicle and has been excellent. I suspected a head gasket minor leak and as I took the head off the block, I noticed the exhaust manifold is super rusted near the mating surface with the block. Please see the pics. I’m not a professional mechanic so I have no experience to judge how bad it is. I can see carbon buildup around the duct perimeters and a bit further in the case of the outer 2 ducts. Looking at the pic of the front of the manifold, I don’t see any obvious metal fatigue failure.

I’ve heard that these manifolds have a manufacturer defect where they crack in the center outer part of the ducts and the mating surface bows. Based on the photos, it appears the outer ducts may be sealing less?

Is the amount of rust on the mating surface too much to seal properly with a new gasket? Can it be sanded down? I doesn’t appear the mating surface was designed to be completely flat… there is a rectangular area in the center that protrudes the main surface… I wonder if sanding that part down is inconsequential?

Are there any tolerances on curvature like there is on the head?

Any advice is appreciated.

Don’t be too agressive when cleaning it up

this might be sufficient

you clearly need to remove any rust that is loose and flaking off, but not so much “good” metal that it won’t seal up

After cleaning it up, you can throw a straightedge on it and give us a few figures, if you like. For example, see what the fattest feeler gauge you can slide in between the straightedge and the manifold assembly. But I wouldn’t go out and buy a straightedge, if you don’t already possess one

Doesn’t look that bad to me. As long as there aren’t chunks coming off I’d probably slap it back on the car with a new gasket. Exhaust gaskets are squishy, so they’ll conform to ripples in the mating surface.

That header is made out of cast iron, and that stuff rusts at the drop of a hat, so seeing rust there is not at all surprising. The tolerances are basically “Is it leaking? If not, it’s fine.” :wink:

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Most exhaust manifolds look a lot worse than that after 5 or 6 years . Just get the loose stuff off with a brush and be happy you were able to get the studs off , LOL .

OEM exhaust manifolds are usually very thick cast metal. It would take decades for any rust to cause a problem. Clean it up…And paint it if you want. Make sure to use high-temp paint.

Doesn’t look particularly bad or anything to me. Cast iron is gonna rust. If you want you can get a metal wire brush and see if you can get some the mating surfaces cleaned up a bit. Or you can get stainless steel header and call it good.