I am likely going for my 4th manifold and was wondering if there is a record for how many that people have done on their vehicles. The original lasted about 9 years and was replaced by the gm on the 10 year extension warranty. It lasted about 1.5 years. :-( Its replacement on my "dime" was a dorman that lasted about 6 years. I haven't pulled the heat shield yet to look around but the noise is telling me that it ain't going to be something else... although I hope it isn't a bunch of snapped bolts or even one for that matter. This could be the death kneel for the truck. :-(
Exhaust manifold record?
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Mooseman
Moderator
That is weird because your 08 should have the "best" manifold version for this engine with the split in the middle. Not to rub anything in your face, at almost 200k km, I'm still on my original 07 manifold, which was still the one piece. Maybe they screwed up on this version trying to fix it. Wouldn't be the first time.
Maybe you could go for a set of headers instead
. Seriously though, it is a PITA but depending on the condition of your TB, may still be worth it compared to buying another vehicle at these overinflated prices (and getting worse because of, you know....)
Maybe you could go for a set of headers instead
. Seriously though, it is a PITA but depending on the condition of your TB, may still be worth it compared to buying another vehicle at these overinflated prices (and getting worse because of, you know....)
In a Nut Shell...
Bad Motor Mounts presage -=All=- Manifold Cracks in the Down Runners and -=All=- Manifold Bolt Failures.
Bad Motor Mounts presage -=All=- Manifold Cracks in the Down Runners and -=All=- Manifold Bolt Failures.
I am not sure what that actually is... but I did take picture of the GM replacement that they did and the dorman that is currently on. Iirc, they looked the same (I have to dig it up) BUT iirc, the gm didn't align correctly when compared to the dorman.... the gm was "stretched" in some form. It is kind of funny as when I brought it in to the gm dealer for the warranty work, one of the guys there "grimmest" with "ugh one that we will have to heat up to make it fit"... I said "how can you do that... its cast?" He reply... "we heat it up enough to get it for "flex a bit"... !!! Of course, I wasn't there for the effort and assumed they know what they are doing based on "experience", both in and out of warranty...
I suspect my towing heavy might put a strain on things a bit more but certainly makes me think about things in terms of remaining "life span" of this vehicle. It might be "driving" me towards a jeep grand cherokee for similar tow and size.
I dug up the picture....
I see the split that mooseman was referring to... both have that design. You will notice that the "older one" (gm replacement) is "stretched" when compared to the new one (background). I don't believe that is by "design". It is more than likely some "manipulation" either by the truck and by "someone" else...
I find it some what interesting that the truck could have caused the "stretch" since that would mean that it some how "moved" with all the bolts in place and it would only be possible if the block / head itself expanded. Looking at the distance... surely the head would have split also.As suggested, the truck doesn't really owe me anything at thing point so I am usually one to keep things out of the "recycle bin" unless it is totally "unrepairable" (ie. no parts available, nothing to attach to, etc).
Also as suggested maybe the motor mounts are past their time (good possibility at this age and mileage). Once I get a good look at the manifold to see what is / was going on, hopefully I will have a better understanding.
Maybe the old adage, "things come in threes", means that the fourth will last "forever"...
Another funny thing... just looked up rockauto and the dorman manifold is on "closeout special" at $112Can... ! and a further interesting thing on the description... quote: "this replacement exhaust manifold is constructed of ductile iron to prevent future warping and cracking".... so maybe one CAN manipulate a cast product.... but does it help or hinder its lifespan.
Of course, the tariff situation also likely be just as funny...
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Mooseman
Moderator
If your current one is a Dorman, it should be the "improved" design with the ductile iron as they have been putting out improved manifolds for all years of the GMT360s for a long time. Maybe you just have a broken bolt(s) but then that will still mean removal of the manifold to remove that bolt(s).
Could be a bolt issue BUT as you say it still involve a R&R effort. I will know more once I get the shield off. I guess the question is if the effort is done to take the whole thing apart, is it worth the $170 (according to rockauto's total) to get a new manifold put in there after?
Mooseman
Moderator
Hmmmm. You might have to tack on an extra 25% to that. I know I stopped buying anything from RA because of that. If the manifold is good, I'd save my money.
Looking at the Dorman, it does say it has a lifetime warranty so if it is cracked and you have the invoice, you can get a new one free.
Looking at the Dorman, it does say it has a lifetime warranty so if it is cracked and you have the invoice, you can get a new one free.
could be... although that was the price from the check out... but of course, it is going via ups which could get caught is all kinds of "froth" at customs.
anyway, I got the heat shield off. The manifold is cracked at least at the where the two "sides" meet to go to the exhaust / cat. :-(
See attached picture. It might even be cracked (burnt) higher on one of the port towards the engine but I can see "around the corner" of the port.... the second port after the split towards the back half. It could just be poor casting surface.
So my issue / fear is always about breaking bolts especially in bad places... this is one of those jobs where it is high risk. The other area is getting the three bolts at the "throat" to the exhaust. One of the bolts is hard to get at AND of course, probably really "welded" to the threads of the manifold yoke.
Will this job be "snake eyes" or "7's"?
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Mooseman
Moderator
Thanks... from the noise, I figured it was either blown out near the yoke maybe but I could see that it was intact there. What I can't believe is how loud it is from a crack that looks like a "sliver". Anyway, I did the rockauto buy for $200C (includes the doorman manifold, gaskets, exhaust flange 3 bolts plus donut and then added 12 dorman bolts) ... all in with ups for next week. Still deciding whether to chance the repair or have a mechanic do it.I was hoping for you.
Mooseman
Moderator
At this point, the bolts are all there ... but as they say, you don't know what you don't know. A bolt can be broken at the head BUT rusted / held in place in the manifold "ear" / tang hole. I am currently spraying penetrating oil on all points. The replacement isn't due here til thursday.... I will also a say a few prayers along the way.
xavierny25
Member
I'm currently on my 4th exhaust manifold. First one was replaced under warranty and unfortunately did not last near 9yrs, probably 5yrs.
This last time (2yrs ago)I replaced the whole exhaust system. Dorman manifold and walker cat back.
As @mrrsm mentioned, checking the motor mounts and replacing as needed is a great idea. I'm on my second set of mounts with 272,000+ miles.
Ya, I see that as one of the suggestions made on rockauto in the notes... and here. I guess what I don't see / understand how this can be in my case. If the mount was an issue, how is that causing the fracture that I posted.... :-(. My thoughts is if it was a mount problem, I may have bolts broken from the motor "torquing" clockwise and the whole system "wishboning" with the strain at the engine block connection, breaking bolts OR breaking the manifold near the exhaust / yoke joint, horizontally not vertically as shown.
I am thinking in my latest case, age and possibly "water ingress" from "road splash" caused an issue. I think that it happened somewhat suddenly during some "melt / freeze" cycles here where there was lots of water on the road way but temps were just below freezing... we like to use lots of salt on the roads, its good for the cars and environment...
In the previous case, I suspect that GM did their the "stretch magic" to fit the manifold on as the "mechanic" groaned about when I bought the truck in. That "magic" was weaken the manifold and shortened its life to less than 2 years.
"I guess what I don't see / understand how this can be in my case. If the mount was an issue..."
As preface in response to your mentioning this, my reading of your Threads and Posts is part of WHY I am now able to understand so many things... so much better... Thanks to your participation here at GMT Nation.
It follows that more than most Folk, I understand and recognize that "All Knowledge is Derivative..." and in this case, what follows in hand to bear out WHY the Bad Motor Mounts are CENTRAL to solving this problem by replacing them at the same time when installing a New Exhaust Manifold with the New Fasteners... Comes NOT from me... But from a Brilliant, Elder Greek Mathematician to assist with our understanding of Geometry... and LEVERAGE:
His name was and is... Archimedes. He once postulated, "Give me a Place to Stand, a Fulcrum and a Long Enough Lever...and I could Shift The Earth".
Consider the Design of the Exhaust System from Nose To Tail in the Very Tall and Top Heavy GMT360 4.2L LL8 Engines with the tendency to REALLY Tip from Side To Side during RPM increase and decrease as well as when making Left and Right Turns... and STRESS those Manifold Bolts and the Exhaust "Y" collection point as the CAT Can and Piping RESIST this dynamic motion.
Notice the similarities in the Mechanical Advantage that the CAT Piping sustains all the way down to the Muffler and Tail Pipe have over the Motion of the Engine Block ROTATING ON ITS CENTER LINE ...WHILE IMPARTING A TORSION THAT STRESSES THOSE AREAS OVER AND OVER ...JUST PAST THE FULCRUM IN THE "Y" PORTION OF THE E-M WEBBING ... IN THIS LENGTHWISE ANALOG OF:
(1) A MASS (2) A FULCRUM AND (3) A LEVER.:
Whenever Ductile Cast Iron is Flexed... Over and Over... its internal Crystalline Structure is under constant Tension and Compression ...Over and Over... until those Large, Asymmetric Cast Iron-Carbon Crystals gradually heat up from internal friction and manage to decrease enough in size, such that the local metal areas become Very Brittle and Weak... All the way down to an Atomic Level... and finally, they propagate CRACKS along the Weakest Points of Stress... and the Metal Mechanically FAILS.
In this Case... Observe ALL of the Red Dots in all of the images as being that special location. Failure due to the excessive back and forth motion of the Engine Block moving on top of Failed Engine Mounts in response to increasing and decreasing RPM and Torque... ALWAYS ends in the same, inevitable way ... With Stressed and Broken Bolts Parting and Cracks in the "Y" Webbing of ALL Cast Iron Exhaust Manifolds Occurring. The Physics and Metallurgy involved here are immutable for this unfortunate outcome.
As preface in response to your mentioning this, my reading of your Threads and Posts is part of WHY I am now able to understand so many things... so much better... Thanks to your participation here at GMT Nation.
It follows that more than most Folk, I understand and recognize that "All Knowledge is Derivative..." and in this case, what follows in hand to bear out WHY the Bad Motor Mounts are CENTRAL to solving this problem by replacing them at the same time when installing a New Exhaust Manifold with the New Fasteners... Comes NOT from me... But from a Brilliant, Elder Greek Mathematician to assist with our understanding of Geometry... and LEVERAGE:
His name was and is... Archimedes. He once postulated, "Give me a Place to Stand, a Fulcrum and a Long Enough Lever...and I could Shift The Earth".
Spinning Levers : Handy (Jam) Organization : Free Download, Borrow, and Streaming : Internet Archive
The transmission in the modern motorcar -- the mechanism that makes it possible to have three forward speeds and a reverse -- is a series of levers, levers...
archive.org
Consider the Design of the Exhaust System from Nose To Tail in the Very Tall and Top Heavy GMT360 4.2L LL8 Engines with the tendency to REALLY Tip from Side To Side during RPM increase and decrease as well as when making Left and Right Turns... and STRESS those Manifold Bolts and the Exhaust "Y" collection point as the CAT Can and Piping RESIST this dynamic motion.
Notice the similarities in the Mechanical Advantage that the CAT Piping sustains all the way down to the Muffler and Tail Pipe have over the Motion of the Engine Block ROTATING ON ITS CENTER LINE ...WHILE IMPARTING A TORSION THAT STRESSES THOSE AREAS OVER AND OVER ...JUST PAST THE FULCRUM IN THE "Y" PORTION OF THE E-M WEBBING ... IN THIS LENGTHWISE ANALOG OF:
(1) A MASS (2) A FULCRUM AND (3) A LEVER.:
Whenever Ductile Cast Iron is Flexed... Over and Over... its internal Crystalline Structure is under constant Tension and Compression ...Over and Over... until those Large, Asymmetric Cast Iron-Carbon Crystals gradually heat up from internal friction and manage to decrease enough in size, such that the local metal areas become Very Brittle and Weak... All the way down to an Atomic Level... and finally, they propagate CRACKS along the Weakest Points of Stress... and the Metal Mechanically FAILS.
In this Case... Observe ALL of the Red Dots in all of the images as being that special location. Failure due to the excessive back and forth motion of the Engine Block moving on top of Failed Engine Mounts in response to increasing and decreasing RPM and Torque... ALWAYS ends in the same, inevitable way ... With Stressed and Broken Bolts Parting and Cracks in the "Y" Webbing of ALL Cast Iron Exhaust Manifolds Occurring. The Physics and Metallurgy involved here are immutable for this unfortunate outcome.
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OK... so that might be the case... but I think the 1 year plus for the GM warranty installed manifold seems that the "Ductile Cast Iron is Flexed... Over and Over" happened fast while the 6 year plus one that I installed there after somehow managed to survive even though now the motor mounts have aged an extra 6 years!
Anyway, I hummed and hummed about this while sitting on the replacements parts. I finally got it done by a mechanic (self employed)... my hands and back thank me along with my wife as she did not have to put up with my "grumbles" on how a "simple job" turns into days and weeks of "swearing".
Trunk feels like the "new kid in the driveway"...
Anyway, I hummed and hummed about this while sitting on the replacements parts. I finally got it done by a mechanic (self employed)... my hands and back thank me along with my wife as she did not have to put up with my "grumbles" on how a "simple job" turns into days and weeks of "swearing".
Trunk feels like the "new kid in the driveway"...
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Mooseman
Moderator
Just as an FYI, apparently the 2008-09 would commonly break where yours did. Got that from Calvin (Nivlac57) in his latest info video of the 4.2.