Replacement exhaust manifold cracked?

[ksweeneyjr]

I replaced my exhaust manifold on my 05 envoy xl at 150000 miles about 8 months ago. Just recently (162000 miles) I started getting a weird noise every time I accelerated. It doesnt sound as bad as the first manifold did, but it is recognizable. I took it to my local Merlin for an oil change and had them look at it. They told me it was cracked again. I havent been able to get under the hood and mess around yet. I'm wondering if maybe the new bolts have backed off a little causing this noise, or maybe the cat is clogged causing the manifold to crack again. Any info would be greatly appreciated.

I used the Dorman replacement manifold that was supposed to be an improved design.

 

[IllogicTC]

Clogged cat: Perform a backpressure test!

Loose bolts: Just make a run through all the bolts with a torque wrench set to the proper amount!

Cracked manifold: There's other threads around here concerning this and how to diagnose it. You could check a lot easier if you removed the heat shield and inspected it yourself. People report observing through the passenger side wheel well, where they hear I think what is described as some sort of pinging or something. Search around, you'll see what I mean.

 

[Mooseman]

Contact Dorman for a warranty return and I'm also sure they'd be interested in finding out why it cracked since they profess it as being improved.

 

[mrwitty_1]

I was just wondering if you personally did the replacement or had it done. I tackled this project this weekend and I must say I also used the Dorman manifold along with there mounting hardware. The reason I ask is that mine also had been replaced with a GM manifold or someone had been there for some reason and the rear bolt was broken off yet someone never corrected the problem. The Dorman bolts do not have any thread locker on them and after reading many threads I used a thread sealant that protects against vibration and thread seizing. Sure hope my manifold last much longer than that .... not and easy job !

 

[IllogicTC]

I was just wondering if you personally did the replacement or had it done. I tackled this project this weekend and I must say I also used the Dorman manifold along with there mounting hardware. The reason I ask is that mine also had been replaced with a GM manifold or someone had been there for some reason and the rear bolt was broken off yet someone never corrected the problem. The Dorman bolts do not have any thread locker on them and after reading many threads I used a thread sealant that protects against vibration and thread seizing. Sure hope my manifold last much longer than that .... not and easy job !

Indeed. It was good that you spotted and corrected the issue, and you were wise in doing some research. By the way, nice to have another WV bro around here. I bet Envoy_04 passes through or somewhat nearby your town twice a week

It's also very important that a torque wrench that's known to be in good calibration is used, for obvious reasons.

 

[ksweeneyjr]

I was just wondering if you personally did the replacement or had it done. I tackled this project this weekend and I must say I also used the Dorman manifold along with there mounting hardware. The reason I ask is that mine also had been replaced with a GM manifold or someone had been there for some reason and the rear bolt was broken off yet someone never corrected the problem. The Dorman bolts do not have any thread locker on them and after reading many threads I used a thread sealant that protects against vibration and thread seizing. Sure hope my manifold last much longer than that .... not and easy job !

I did replace it myself. I had a lot of trouble with the cat to manifold bolts, not the actual manifold bolts. My old manifold also was missing the rear bolt, not sure why. Unfortunately I did not use a thread locker just an anti seize. I checked the bolts over the weekend and they were all torqued properly. Could the noise and exhaust smell be something other than a cracked manifold?