Exhaust manifold causing head replacement


#1

I have a dodge pickup and just recently had an exhaust manifold leak. The technician repaired the leak but is not confident on how long it will hold due to damage from the manifold to the head. He is saying that a bump could cause it to leak again and if this happens it will require the head to be replaced. I myself have not heard of this and wondering if this is possible and if there are any other possible repairs over replacing on rebuilding the head?

Thanks for the help.


#2

If it happens again, take it to a mechanic instead of a technician. Seriously, I would need a lot more details to make a judgement on this. I can’t see why the head would have to be replaced or how a simple bump would cause this much damage.


#3

Ummm… without knowing the year, model, and engine we’re kind of guessing blind here.
My blind guess is that since the truck apparently ran fine when it was new, I can’t imagine how a “bump” would suddenly develop in the head. And, frankly, I can’t imagine how a leaking exhaust manifold could cause a “bump” in a head.

Can you provide the year, model and engine? And can you copy exactly what the mechanic wrote on the shop order? You DID keep your copy I hope…


#4

Yes, it’s possible for a cylinder head to suffer damage due to an exhaust leak. The bit about a bump sounds strange but I could theorize that the reason for that statement is that the possibly of constant exhaust flow vibrations and the lever effect of the exhaust system in motion trying to rock the manifold could cause another gasket failure.
That’s grasping a bit but anything is possible.


#5

2002 dodge Dakota with a v8, was told that they repaired what they could but vibration from rough roads could cause the leak again and if that it does the head would need to be replaced. It was done at an exhaust shop but he did not right up and I am getting some of this second hand as I did not talk to the mechanic.


#6

Possibly some of the metal on the flange of the cylinder head was eroded away by an exhaust leak. A new gasket could help fill in that erosion but as to how long it would last is debateable.

The same thing can happen with engine block decks and cylinder head faces during a head gasket leak and it’s especially true of aluminum.
Hot leaking coolant and/or combustion chamber gas being expelled through a head gasket breach can erode material off the faces also.


#7

Exhaust manifolds on the 4.7 L engines are known to warp and cause exhaust leaks (this is not a 5.9L RT is it?). If the vehicle was driven for years with the exhaust leak the cylinder heads could have been damaged. Were the exhaust manifolds replaced? Were they checked with a straight edge?


#8

It is a 4.7 l v8, unfortunately I do not have much of the history on the truck. At this point I am trying to figure out if I should look at selling it or continue with the few more repairs or sell it while the repa it list is short.


#9

The 4.7 is known to have the exhaust bolts break off in the head requiring drilling or extraction. Depending on access to the bolts, this can be a difficult job to repair properly. The manifolds also can warp requiring resurfacing or replacing.

As was stated, if driven long enough a leaking manifold can damage a head.


#10

One of the manifolds has been replaced but I am not sure if the one that is in question was. If it is the head is there any easier fixes than replace or rebuild the head?


#11

If the surface on the head is damaged, it has to be remachined and that means it has to come off the engine. Once you remove the head, it would make sense to go ahead and rebuild it. And if you rebuild it, do you want to put it back on an old block?

If the erosion isn’t too bad, you might find a talented mechanic who can fill in the erosion with a tig welder and the resurface the immediate area with a small die grinder. It won’t be perfect but it might be good enough.


#12

The exhaust manifold gets really hot and is directly bolted to the head. So yes the heat from the exhaust manifold could damage the head, especially if the exhaust gas wasn’t passing exclusively through the sealed ports which are designed to handle hot exhaust gasses, and instead leaking into paths not designed to handle it. Whether this applies in your case OP, only a qualified mechanic or machinist with the parts in front them could say.


#13

Sometimes overheating can warp an exhaust manifold and even warp intake manifold flanges.

I would hope the exhaust manifold flange was checked with a straight edge while it was loose.
Bolting it back up might straighten out a few thousandths of an inch but any more than that and there’s a good chance the gasket won’t hold up.

Also, sometimes what can happen is that the manifold may be straight as bolted to the head. Once the bolts are loosened and removed the manifold may (or may not) have a tendency to curl up so to speak.

I replaced a short block in a Chevy truck once and rebuilt the cylinder heads on an engine which had been seriously overheated.
Once together neither exhaust manifold would bolt up. Start a bolt at one end and the holes got progressively more and more off as I went down the row. The opposite end was a full 1/4" out of whack due to both manifolds curling when they were removed and both were warped to something like .030 out of straight… That’s an extreme case.


#14

The bump could cause it to leak again is on the top of my bogus list. Time for a 2nd opinion.


#15

“It is a 4.7 l v8, unfortunately I do not have much of the history on the truck. At this point I am trying to figure out if I should look at selling it or continue with the few more repairs or sell it while the repa it list is short.”

The two kind of go hand in hand don’t they? You will most likely have to do at least this repair in order to sell it. I think if you find a really good mechanic, like Keith mentioned, he or she could figure something out. You could also probably save yourself a bit by ordering parts online yourself and then bringing them to the mechanic. It’s your call, but I know I wouldn’t by a vehicle in need of a repair like this. It’s probably worth the money either way.


#16

Oh…sorry, I just realized how old this post is. You most likely have already dealt with this by now.


#17

Sounds like this Muffler Mechanic is describing warped headers…yes they can damage a cylinder head if driven with a high velocity leak at the head…but methinks this is just a guy who is trying to repair a leak and working with what he has to work with.

A warped header and doubled up Exhaust Man gaskets will or should put this to bed. Then again… a new Ex Manifold wouldn’t hurt if the old one is warped or cracked…I mean that is how you fix this sorta thing.

Also attention needs to be paid to how the downpipe is attached or not attached to the rest of the vehicle…this is why there are so many “Flex Pipe” sections out there these days. Some mfgs use normal exhaust pipe in the design and then “isolate” the rest of the system with rubber hangars…others are forced to use those stainless steel flex sections to allow the engine some literal “wiggle room”. Not sure of your exhaust makeup tho…Id have to look it up but you do not want the exhaust system to apply forces to the exhaust manifold unnecessarily.

Once a header warps at the head it makes noise…enough noise for you to stop and take a look and not continue motoring… My money is on the manifold or the studs in the head or lack thereof being the real problem…replace whatever is warped or broken it and it shouldn’t be suspect anymore and I would HOPE that is not referring to the head.

I think they told you this because they replaced the gasket on a manifold that was warped, cracked OR the dude broke 3 out of 6 manifold bolts in the process of removal and now knows its held on by the skin of its teeth…or something like that. Wouldn’t surprise me in the least little bit. You need to have a looksie…if it all looks normal and all bolts / studs are present…ask him why he told you what he told you. I doubt the head is damaged Port Wise… Could be Stud wise or thread wise…

Blackbird