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

1Moses1, what you say makes good sense, but the OP’s failure is at the turn on the runner and nowhere near a weld. In this case I don’t think we can say “That’s what headers do.” I’m pretty sure he had another issue by the looks of his pictures. Has anyone else seen something like that in the middle of the runner? Also, it’s in the outside of the bend, not where you would expect water to collect and eat through.

The op’s failure is at the thinnest part of the tubing after it’s bent. Very common. The tails are generally a thicker wall material and less tight radius bends.

your original post asked about risers not tails...

really? i have bent plenty of tubing and i cant see it would be more than a few thousands thinner.

Thanks! My Mercury stock exhaust is already back on, but just changing the exhaust manifold was not the reason for this thread.

And also the least amount of water flow

This is exactly my question and the reason for this thread. What caused this issue? I think everyone can agree on that a stock 496HO is not an extreme engine by any means which is one of the reasons that makes me woundering what is going on.

The failure is in the tubes from cyl 1-4 which have the biggest radius. From cyl 5-8 the where the radius is tightest the tubes looks like new, not a slightest sign of pitting. Can You please explain which part of the exhaust is the tail. I thought it was the part that is clamped on after the collector?

From the pictures that you have uploaded, I see minimal corrosion and a very hot section of tubing at the outside apex of a runner that most likely lost water flow. Do you have a sea strainer? It seems very possible that you picked up some small chuck of crap that blocked flow and you over heated that spot in the tube. If I was in your position I would get another set of the same headers and add a sea strainer. Stock sh!t sucks and stainless marine is just bilge clutter.

I agree with you that this is a heat issue and there is no corrosion. If it only had happen to one of the runners I would also think there was some kind of obstruction but the damage looks almost exactly the same in all runners from cyl. 1-4 while the runners from the rear cyl 5-8 looks like new and as I mentioned before, there has been no discoloration on the polished surface. I do have a sea strainer, and after taking the headers off I back flushed them and the trees without a trace of debris in them. The flow was pretty similar through all the runners if not slightly more through the damage ones.

If it is a problem with lack of water, have anyone heard if it is possible that an air pocket could have formed at the highest point where the damage are or is it just the weak point for water flow? If it is engine related, even if the 496HO is a mild engine can it due to bad injectors create a lean condition that can cause this? Lean condition due to low fuel pressure should have affected all the runners equal or?