I bought new to me 2004.5 CTD 6spd drw 3500 2wd QC. It was 8k with 128k. The exhaust manifold was leaking throught the gaskets so I went to replace them this afternoon and when I loosens the bolts I heard a loud pop and then all the bolts were really hard to remove. Ended up stripping three bolts and when I put the exhaust manifold nxt to one I had in the shop all the holes didn't line up and were a little bit more than a 1/4" off. I cut it up and they actually look pretty good (stock manifold). They are over 1/4" thick wall.

Just though I would see if that happens often. And to say that I got a new truck.

 

That used to happen to me with small block Chevy exhaust manifolds...I had a couple of spreaders in my toolbox to spread them out for the reinstall unless they cracked......Ben

 

Do you mean you only paid $8,000 for the truck????

 

Yes that happens a lot on these trucks and not cause for alarm. It is the result of too hot a manifold and not proper cool down. It will be more prevelant if the bolts or studs are not tight enough. the manifold design is borderline as a one piece design.

Here is what happens: The manifold gets real hot and expands then it reaches a temperature so hot (like cherry red or orange) that the material gets plastic and yeilds as it expands but the head is stronger and maintains the bolt spacing. The head stays rather cool as it has cooalnt in it. Now as the manifold cools as soon as it comes off the plastic stage it stops yeilding and starts shrinking but because it is not plastic and it has decent cross area it can exert tremendous force as it contracts and will slide on the gaskets. The cycle repeats the next time the manifold is heated and this shrinkage continues. The studs relax some due to temperature as well. So this creeping continues until either the manifold breaks or it snaps studs.

It is most common in drag racing or applications where very high heat is applied quickly for short times and the cycle is repeated often. But it can occur over time in regular use towing. To avoid it either use a 2 piece manifold or reduce the temps and ease into the load and allow slow cool down period idling.

Another interesting thing that you can look for in your used manifold is thinning, especially in the walls of the outside of bends. Cast iron and ni-resist alloys that most manifolds are made from start vaporizing around 1,300F. The gases flow the fastest on the outside bends. You may notice the outside of the bends are 1/2 as thick as other areas. Eventually, they will wear through and crack. This is the main reason for the 1,250 f recommended limit for towing applications. Ni-resist or stainless, both with nickel added can go higher. For long life 1,250 F is a good upper limit.

This same effect can be demonstrated by bending metal with a torch and not using any force. Contrary to intuition, a Welder will heat the side of the metal bar he wants to pull in red or orange hot. The remaining metal on the opposite side that is cool resists the expansion of the hot side and the hot side plastically deforms as it yeilds. Then when it cools it pulls under contraction and causes the bar to be bent in the direction of the side originally heated. It is surprising how much this effect will bend the metal.

 

Makes sense, I cut the manifold into 5 pcs and some sides aren't same thickness all the way around. 8k just for the truck is right! But it has a dent in the tailgate...lol.