Exhaust Manifold Leak (Suspected): Tips, Suggestions, Experience?

[CruelJung]

I have been driving my '08 Yukon XL for nearly four years now, and it has always made a 'ticking' noise on cold startup. This noise subsides within a minute or so, as the engine temperature rises. No CEL or codes. Over the past four years I have been gaining more automotive knowledge and competency, as well as developing a general obsession with this vehicle--how it runs, how it sounds, how my maintenance/repair choices will affect a trajectory towards supercharging one day...

So, I started chasing this 'ticking' noise a few months ago because I noticed an exaggerated form of it under load while driving with the window down. When looking for a busted exhaust manifold bolt, I found that the second-to-rearmost manifold bolt on the passenger side was loose enough to turn with my fingers. There was also soot visible in a few areas above and below the manifold flange. I torqued all 12 bolts to 18 ft. lbs.--noting that all but one bolt were under 11 ft. lbs.--and the result was less noise for less time when cold starting and still noise under load.

Having some free time, last week, I decided to revisit the manifold bolts again because the cold start 'tick' duration seemed to be increasing. Sure enough, the bolts were under the 18 ft. lb. torque spec again and--once re-torqued--the cold start noise level and duration were reduced.

Presuming that the sound (when cold and under load, but dissipating in idle from cold to operating temperature), visible soot, loose bolts (potentially walked out and damaged gasket seal?) point towards an exhaust leak, I am planning to do the following:


1. Replace the current, rusty hardware with ARP header bolts
a. Leaning towards ARP 434-1102 (SS, hex)
b. Considering ARP 434-1301 (SS, stud/nut)

2. In conjunction, replace the exhaust manifold gasket (without removing manifold entirely--i.e., not disconnecting from Y-pipe)
a. Leaning towards OEM (Genuine GM), AC Delco, or Mahle
b. Considering a Remflex gasket or double Remflex gasket to compensate for any warping of the manifold

3. See what happens
a. If the sound persists, I will try to tighten the studs (manifold to Y-pipe).
b. If sound STILL persists after "a.", then I will remove manifold entirely to inspect, replace manifold-to-Y-pipe gaskets, and potentially replace the manifold.


With all of that said, do any of you with experience have some advice for the materials, process, or--for that matter--diagnosis?

 

[j91z28d1]

just my opinion and others do completely different and it works well for them too. but I like exhaust manifold studs. I feel like stainless steel is to soft for small m8 these engines use. I like the Dorman ones of all things, originally found them listed for a mustang, since they use the same size. but different amount M8x1.25 is the size.) don't rust are 10.8 grade and the nuts are flanged crimp locking nuts, so I've never had one come loose.

to me the oem gaskets have been good, but I have no experience with the others, they might be good too.

for exhaust leaks, the best way I've found to find then is the mechanic stethoscope but remove the metal tip so you have a open hose, run that hose along anywhere you might have a leak and you'll hear a puff puff puff clear as day.

 

[j91z28d1]

these were on the car about 5 years..

I only recently removed them because the headers I bought came with titanium Hardware, which I'm scared is to soft was well, but I gotta admit it's kinda special looking and when you put 2500$ headers on your car, you do dumb things for looks sometimes haha.

the arp bolts are strong, but without a locking thing, I'm not sure they are really much better for you. someone found a set of bolts that are split with a set screw in the middle. once you tq the bolt you tighten the set screw to lock the bolt. I've used them on old school 3/8 sbc stuff because you need all the room you can get and studs don't work. had good results with them in that size.

 

[CruelJung]

just my opinion and others do completely different and it works well for them too. but I like exhaust manifold studs. I feel like stainless steel is to soft for small m8 these engines use. I like the Dorman ones of all things, originally found them listed for a mustang, since they use the same size. but different amount M8x1.25 is the size.) don't rust are 10.8 grade and the nuts are flanged crimp locking nuts, so I've never had one come loose.

to me the oem gaskets have been good, but I have no experience with the others, they might be good too.

for exhaust leaks, the best way I've found to find then is the mechanic stethoscope but remove the metal tip so you have a open hose, run that hose along anywhere you might have a leak and you'll hear a puff puff puff clear as day.

these were on the car about 5 years..

I only recently removed them because the headers I bought came with titanium Hardware, which I'm scared is to soft was well, but I gotta admit it's kinda special looking and when you put 2500$ headers on your car, you do dumb things for looks sometimes haha.

the arp bolts are strong, but without a locking thing, I'm not sure they are really much better for you. someone found a set of bolts that are split with a set screw in the middle. once you tq the bolt you tighten the set screw to lock the bolt. I've used them on old school 3/8 sbc stuff because you need all the room you can get and studs don't work. had good results with them in that size.

View attachment 439504

I am considering shorty headers if I have to replace my iron manifolds for any reason, but would prefer to keep my OEM metal until further along in my performance upgrade arc. In fact, while this vehicle is my daily driver, I do have access to a sandblaster and large belt sander if I wanted to remove rust and warping from my current manifolds--it would just put my vehicle off the road for a few days.

I like the ARP product from what I have read and understand in these forums, especially regarding the re-use aspect because I have no idea how many times I will have to re-do or check my work--not to mention further upgrades in the future. The reason I am considering the stud/nut style (from ARP) is because it seems like it would make the manifold removal/replacement easier with the studs as guides. I didn't mention it earlier, since I am very much leaning towards ARP, but I have also looked into the locking style header bolts with oblong washers and c-clips. However, I prefer--in theory--the less complicated and seemingly invincible ARP hex bolt with the addition of threadlocker.

I am curious, though, why are you concerned about stainless steel and titanium being too soft for this application?

Thanks for the tip about the stethoscope! I've meant to purchase one for some time now and always forget--finally bought one.

Regarding the gasket, I think I will go for the OEM style first and see if that works. I was only put under the impression that doubling up on the gasket can work by some anecdotes from automotive-minded individuals I know, but I think they were referring to the composite style gasket which is more or less of consistent thickness. The OEM, MLS gasket for these Vortecs seems to have a greater thickness around port holes, so I don't think doubling would be a good idea unless someone with experience can tell me otherwise. Additionally, I've read that while these thicker, composite aftermarket gaskets (Remflex: 50% crushable graphite, etc.) give a great seal initially, they tend to break and blow out later.

I took a video of my cold startup noise and will post it here, shortly.

 

[CruelJung]

I have been driving my '08 Yukon XL for nearly four years now, and it has always made a 'ticking' noise on cold startup. This noise subsides within a minute or so, as the engine temperature rises. No CEL or codes. Over the past four years I have been gaining more automotive knowledge and competency, as well as developing a general obsession with this vehicle--how it runs, how it sounds, how my maintenance/repair choices will affect a trajectory towards supercharging one day...

So, I started chasing this 'ticking' noise a few months ago because I noticed an exaggerated form of it under load while driving with the window down. When looking for a busted exhaust manifold bolt, I found that the second-to-rearmost manifold bolt on the passenger side was loose enough to turn with my fingers. There was also soot visible in a few areas above and below the manifold flange. I torqued all 12 bolts to 18 ft. lbs.--noting that all but one bolt were under 11 ft. lbs.--and the result was less noise for less time when cold starting and still noise under load.

Having some free time, last week, I decided to revisit the manifold bolts again because the cold start 'tick' duration seemed to be increasing. Sure enough, the bolts were under the 18 ft. lb. torque spec again and--once re-torqued--the cold start noise level and duration were reduced.

Presuming that the sound (when cold and under load, but dissipating in idle from cold to operating temperature), visible soot, loose bolts (potentially walked out and damaged gasket seal?) point towards an exhaust leak, I am planning to do the following:


1. Replace the current, rusty hardware with ARP header bolts
a. Leaning towards ARP 434-1102 (SS, hex)
b. Considering ARP 434-1301 (SS, stud/nut)

2. In conjunction, replace the exhaust manifold gasket (without removing manifold entirely--i.e., not disconnecting from Y-pipe)
a. Leaning towards OEM (Genuine GM), AC Delco, or Mahle
b. Considering a Remflex gasket or double Remflex gasket to compensate for any warping of the manifold

3. See what happens
a. If the sound persists, I will try to tighten the studs (manifold to Y-pipe).
b. If sound STILL persists after "a.", then I will remove manifold entirely to inspect, replace manifold-to-Y-pipe gaskets, and potentially replace the manifold.


With all of that said, do any of you with experience have some advice for the materials, process, or--for that matter--diagnosis?

Below is a video of my driver side wheel well during a cold start, after I re-torqued all the manifold bolts. It begins 20 seconds or so after I started the engine, but it captures how the sound dissipates within that minute time frame.

 

[j91z28d1]

I think I'd find it confirm you have a leak before taking it apart. it's been my experience these metal gaskets don't blow out. that's why the clamps work so well. my yukon was leaking from a broken bolt, probably been like that for years. added a clamp and it sealed right up, didn't need to replace gaskets.

as for ss and ti. my feeling is the m8 bolts are under sized for the manifolds as they should have been the next size up and we wouldn't have bolts breaking off in the heads. yeah gm could have used stronger bolts, but no one else needs to do that to seal manifolds. they just size bolts correctly.

ss and ti are usually softer than steel bolts and these days most boot/studs are plated to avoid rusting.

arp might be doing something special to their ss to make it strong as standard? but the ss hardwear I deal with is soft and mostly annoying.

I've had good luck with the $20 stud kit with lock nuts that were in stock at by local O'Reilly. so I usually recommend those. since arp is very expensive, being used on a daily driver and don't have lock nuts?