New to me boat with twin 454 Mag EFI’s @ 5xx hrs each (presumed to be original sealed merc engines)

I’m replacing the elbow gaskets as part of my maintenance routine. One side of the manifolds on the port engine shows this pitting after I removed the old gasket and wire wheeled the surface clean.

This makes me worry the new gasket won’t seal properly if I install it dry without any rtv. Is this typical? Corrosion wise the coolant passages don’t look bad at all from what I can see. This was a primarily fresh water boat.

I would definitely clean that up more with a grinder and then check to make sure it is flat

That appears to be that metallic looking gasket material still left. Wire wheel usually doesn't hack taking all that stuff off from my experience.

you know you’re probably right about that. I was having scrape off a lot of the gasket material with a chisel in certain spots that looked like the base metal at first.

what do you recommend using to clean these manifold tops with? I guess I’m hesitant to hit it with a flapper wheel as I don’t want to make the surface uneven but if that’s what works then I’ll try it out.

I would color the entire gasket surface of the manifold with a magic marker, then gently use a large flat file to remove old gasket remnants and all the ink. Just go slow and keep the file flat against the surface at all times. The ink will let you know if you're too low or too high.

razor blade

Thank you guys for the suggestions. I think the file will work great. Never would have thought of that. I’ll report back on the weekend.

The file works well, I've done it in the past.. I even do it on new manifolds to make sure the surface is flat. Just make sure you go at it from different angles and that will help average out the material removal and will give you the best chance of a flat surface. And the area you need to be absolutely sure you get is the small wall between the exhaust port and the water jacket as any leaks there are a big problem.