3.0GS MBYMCE Exhaust manifold leak

[bigtoe]

Again!!!!!
Well in the last 5 years I’ve had to replace a leaking manifold! The second time the manifold was just within warranty.
Now the last time I did this 2 summers ago I went for a genuine part for both manifold and riser.
Yesterday I felt the boat start to idle rough after 5 mins or so when changing boarders over and I just thought oh no not again!!
Took the riser of today, yup
Loads of water in manifold , hoped it would be the gasket , filled the manifold with water to do a quick test for leak and yes water slowly started to seal in to the exhaust section.
So what to, I don’t think I’m doing anything wrong , but why have so many failed??
Thanks

 

[alldodge]

Put a straight edge on the head intake/exhaust ports

 

[bigtoe]

Thanks for reply but what would that prove with regards to why these manifolds keep developing a leak from water way to exhaust

 

[alldodge]

Yours may not be alone, but having not heard another case similar to same issue, and not knowing exactly where the crack is, I'm thinking the man is put in a bind.

If the head isn't flat within 0.003 then when its fastened there is enough binding/warp transferred to the man. Then the heat cool cycles will cause a crack later

 

[Bondo]

Again!!!!!
Well in the last 5 years I’ve had to replace a leaking manifold! The second time the manifold was just within warranty.
Now the last time I did this 2 summers ago I went for a genuine part for both manifold and riser.
Yesterday I felt the boat start to idle rough after 5 mins or so when changing boarders over and I just thought oh no not again!!
Took the riser of today, yup
Loads of water in manifold , hoped it would be the gasket , filled the manifold with water to do a quick test for leak and yes water slowly started to seal in to the exhaust section.
So what to, I don’t think I’m doing anything wrong , but why have so many failed??
Thanks

Ayuh,..... Where it's cracked would be a good clue,.....

 

[bigtoe]

That’s part of what the problem
Is there is no way to tell where the crack is or hole, it’s internal between the exhaust and water way, no cracking or anything that looks wrong where the manifold joins the head, except of course for the rust showing in the exhaust ports

 

[alldodge]

Shouldn't have any more rust on the exhaust ports then the intake. What's the gap difference between intake and exhaust? Carpenters framing square or other straight edge

 

[bigtoe]

Thanks all dodge , back on the boat tomorrow , however the rust in my mind is due to water leaking from the waterway across to the exhaust way. The upper route of the intake does appear to have water leaking into it