Leaking header, but not a crack
 

https://cimg2.ibsrv.net/gimg/www.off...30b953671e.jpg
1. Cut out hole
https://cimg9.ibsrv.net/gimg/www.off...0653b8e0cb.jpg
2. Outside of the inner pipe
https://cimg5.ibsrv.net/gimg/www.off...4776da16cd.jpg
3. Inside of inner and outer pipe
https://cimg6.ibsrv.net/gimg/www.off...4ae9eea963.jpg
4. Inside of inner pipe

I bought this set 7 years ago very aware of the risk for leaks. Therefore I have had dual water pickups for safe water supply and have flushed the headers after every outing even though I´m in very brackish water.

Last season I got water in cylinder 7 and 8, took the headers off and pressure tested with water and found out that there were leaks, not from the welds but from somewhere inside the pipes from cylinder 1-4. Water then poured down through the collector down into cylinder 8 and 7.

I used a camera probe and located the leaks on the outer radius at the highest point of the pipes from cyl 1-4. Pic. 1 shows the hole I cut out. Pic 2 shows the outside of the inner pipe. Pic 3 shows the inside of the inner- and outer pipe, You can clearly see spots of soot on the outer pipe. Pic 3 shows much better how pitted this leaking area is, looks almost corroded. On the left side I have cleaned it with a steel brush.

The engine is a bone stock 496HO, the PCM has not been reflashed, nothing but the headers are done to it. I have never had an overheat alarm and there have never been any discoloration on the header so what have caused this? Could it be the fuel, we have 5% Ethanol in the fuel here? Or could it be a lean condition in cylinders 1-4 due to bad injectors? If that was the case wouldn´t it be damage to the exhaust valves then? All pistons, exhaust valves looks fine as does the exhaust pipes from cyl 5-8.

The reason for this post is to find out what has happened, if the headers is made from the right alloy it must be engine related or?

I am grateful for some help and input from the engine gurus here and/or others with knowledge/experience of this issue.

You don´t have to point out that this kind of a header will leak sooner or later, I have read that in lots of header threads.

Thanks!

You already have your answer. Headers wear out, simple as that.

On a stock 496 headers aren't worth the money or aggravation IMO.

Buy some SS marine or stock mercury exhaust and be down with it...

You got 7 years out of them,that seems like a good run for headers.Get some Stainless Marine exhaust and not have worry about exhaust leaks anymore.

So why are stainless marine risers so impervious to failure? They are jacketed stainless tubing also, correct? I think you may have developed an obstruction in the water tree that feeds that side. It looks like extreme heat to my eye. Aluminum manifolds would have melted right through. I know of a Thunder and Lightning header that had melt down from such an occurrence.

I don’t know why;but they just fail,my tailpipes are engraved from 1990 I have pressure tested them 3 different times and still fine.

They are cast as well. Website says stainless Marine is aluminum? Is that true?

a failure in the tail, although not impossible...doesn’t happen often. most header failures occur in the collector which is also where most of the welding happens. The stainless marine headers don’t use a welded collector, instead it’s casted. This eliminates concerns of weld cracks, heat distress, etc.

the general concensus is that the method of manufacturing greatly increases the life and reduces risk of failure.

The manifolds are cast alumium