My original manifold cracked a year ago (almost exactly) at about 28,000 miles. The OEM replacement I bought from Morris recently cracked as well. They sent me a new one under warranty but I have a bad feeling I'll be doing this again in a year.

When I removed the manifold I noticed something unexpected... the second and third cylinder exhaust ports had small piles of dust or sand in them, right near the end where the manifold mounts. I have to think this got in from the flange flexing rather than through the engine but that's pretty hard to believe as well. Does anyone have any thoughts?

I was also wondering if anyone had replaced the collector bolts when doing a manifold swap? Mine we rusty the first time and worse now. I was thinking of going with stainless bolts and double nutting it to make sure they don't loosen (since nylocks would melt).

Thanks!

 

Hmm pretty strange on what you are calling dust. Although it may be possible I'd guess it was more something like oxidation of fuel vapor or something. I would also not use stainless bolts to put on headers. Most headers are put on with stretch bolts designed for one time application. You coat with anti seize then when you torque to spec they stretch slightly to prevent backing out under heat cycles. If cracked manifolds are an issue you might consider checking to ensure that the deck of your head is not warped or needs to be milled. Another thing you might consider is using a copper gasket.

 

I was quite surprised by what I saw. That would be a lot of oxidation, especially in less than 10,000 miles. One thing I didn't mention is that I don't have any fender liners installed and I do go offroad once a month or more, often in dusty environments.

I wasn't planning on using stainless bolts into the head. I'm thinking about the two bolts that connect the manifold to the rest of the exhaust (at the collector).

The manifold is cracked where the pipe for the front cylinder meets the collector. It's a large circular crack, almost like the section is spalling out. The flange looks fine.

 

You may want to check something off the wall like the motor mount ... the root cause for the chronic header cracks at the same spot on 4.0L Jeeps.

 

Motor mounts are solid. Unfortunately, cracking exhaust manifolds are very common on 2007-2011 JK's.

Everybody knows that cast iron exhaust manifolds are a new, cutting edge technology so Chrysler can be excused for having some problems as they implement this exciting automotive development...

 

Jeep Engineering.... amazing. Must be the same guy with a PhD sitting in a corner for 40 years. Paper stacked up to the ceiling, smoke stained file cabinets and Steelcase desk.

We had one of those. I got him kick-started again with Lean and running around the building doing spaghetti diagrams...

 

Hmm what a strange place for a header crack. If the flange to the head is good i would probably rip it off break out the grinder and just weld it up. Ya stainless bolts at the collector should be fine. Might be able to find some nice tube headers as well.