Exhaust Manifold Leak at Coupling Joint

[Bill R]

On a semi regular basis I check the exhaust manifold for cracks or gasket leaks as it is a common issue with the 400ISL in Class A rigs.  I had to replace the gaskets about a year ago and everything was going great, until this last time I checked.  At first I felt an exhaust leak on the 2 port section and though it was a crack.  But feeling a little more, kind of hot on the fingers, the exhaust leak is coming out of the manifold coupler joint on the engine side.  It is hard to feel at idle, but at 1400 RPM you can for sure feel it.  It is a very tiny area of where the exhaust gas is escaping.  See the pic below.  If you zoom in, you can see a little bit of pitting starting to form from the leak.

How does this happen?  I can guess that the manifold has warped a bit?

The obvious fix would be to replace the entire manifold with a new one.  $900 with my free labor.  But since this is not an integrity issue with the manifold, are there other options?

1) Use JB Weld Extreme Heat and fill in the gap where the leak is?  https://knowhow.napaonline.com/how-to-use-jb-weld-extremeheat/ 

2) Take to a muffler shop and see if they can weld where the leak is?

3) Loosen the manifold bolts and try to mate up the joint better?

4) Other thoughts?

 

 

[jacwjames]

Surprised it's leaking there as when I had to replace my manifold on my 8.3 ISC I could get the two apart and the replacement was a very tight fit.

I'd try the JB Weld Extreme first and see what happens.  I doubt the options would work.

[Gary Cole]

Bill there is clearly a crack at the area of the leak which is probably going to continue down the length of the manifold. Might drill a small hole at the end of the crack in order to stop the spread and try the JB weld as Jim suggests.  Nothing to lose for a small effort and a lot to gain if it worked.

Edited May 3, 2023 by Gary Cole

[nvrtoofast]

Welding on cast iron is very difficult and takes a very knowledgeable welder to do it. It will require grinding, preheating and post heating. I would suggest NOT doing this option.  Will likely cost more than the manifold.

Typically not a fan of JB and am unsure of how it would react to the metal and the temperature.

I would like to know how hard it is to change out the gasket and the whole manifold. I know mine is leaking and have not had the time to deal with it.

[Bill R]

@Gary Cole Wow!  I hadn't noticed the crack, but I see it now.  It is coming out of the joint area and explains why it felt like it was leaking out of the joint, but it is not, now that I see the crack.  I would have to remove the manifold to drill a hole, so if doing that work, I am going to just bite the bullet and replace the manifold.  I may in the interim use JB Weld to stop the leak and see how long that lasts.

@jacwjames Well you are right about being surprised if it was leaking out the joint.  It is a crack.

@nvrtoofast Yes I read about welding cast-iron and being a challenge, and now that I see the crack, my thinking is now just replacing the manifold.  The challenge is getting the manifold bolts to bust loose without breaking them.  There are a couple of good videos out there.  Just google "Monaco 400ISL replace exhaust manifold".  It is not that difficult once you get the bolts loose.  I put Loctite Anti-seize on my bolts when I changed the gaskets, so should be a lot easier this time.

[jacwjames]

10 hours ago, Gary Cole said:

Bill there is clearly a crack at the area of the leak which is probably going to continue down the length of the manifold. Might drill a small hole at the end of the crack in order to stop the spread and try the JB weld as Jim suggests.  Nothing to lose for a small effort and a lot to gain if it worked.

Good catch, I didn't see the crack when I first looked at the photo, clearly a problem.

Probably only a matter of time when it will get a lot worse.   Pay me now or pay me later type scenario. 

Are you capable of changing yourself???  I paid $600 for manifold, gaskets and all the bolts including turbo mount bolts in 2015.  Now the manifold alone is $600.  Took me ~4 hours to remove, 8 hours to reinstall mostly because of access and I kept dropping stuff (tool or parts) to the ground had to go out an retrieve.    But a member on IRV2 +1 year ago that Cummins has come up with a flat rate charge of $2500 to change the manifold, go figure. 

 

Edited May 3, 2023 by jacwjames

[Bill R]

6 minutes ago, jacwjames said:

Are you capable of changing yourself???

Yes, put new gaskets on about a year ago.  Took maybe 4 hours to disassemble, 2 hours to put back.  This time hopefully faster since it is a second time and bolts have anti-seize.  Gaskets hopefully are still good, only 1 year and 6,000 miles on them.  From shopcummins.com; 2 port manifold $259 + Tax, 4 port manifold $582 + Tax.

 

[jacwjames]

26 minutes ago, Bill R said:

Yes, put new gaskets on about a year ago.  Took maybe 4 hours to disassemble, 2 hours to put back.  This time hopefully faster since it is a second time and bolts have anti-seize.  Gaskets hopefully are still good, only 1 year and 6,000 miles on them.  From shopcummins.com; 2 port manifold $259 + Tax, 4 port manifold $582 + Tax.

 

Well, practice makes perfect, should be able to shave some time off. 

Good Luck

[Rikadoo]

With the adding of anti-sieze go one more step and run a tap in all the holes, then use a air hose to blow out the residue. Also in regaurds to the exhaust leak have you concidered there may be a restriction forming in the muffler causing pressure lookin for a way out. The new muffler is a straight thru design, its alot quieter than i thought it would be.

[Bill R]

@Rikadoo Can you share a little more about the new muffler? Type, design, supplier?  Was your old muffler collapsed and causing back pressure?  And would that cause more blow-by out the crankcase vent?

[klcdenver]

I installed a Turbine AT4040 by Aero Exhaust . It is a quit or quieter than the stock muffler plus 25 to 30 ponds lighter. I am very happy with it. Sorry cannot get a link to paste that will open.

 

[Rikadoo]

The muffler i bought was the Areo 3030XL, i live in the easy bay in ca, so i had Steve from West Coast mufflers install it. He will do motorhomes on Saturdays only.

as for the old muffler it was leaking an when he pulled it off it had something loose inside, an call me nuts but i can swear the motorhome is smoother to accelerate an the engine runs smother🤪

[Robert92867]

With the manifold removed, it would be a good time to drill and tap for a pyrometer

[Rikadoo]

It was, i did… its for the Banks Stinger kit

[dl_racing427]

On 5/4/2023 at 8:46 PM, Rikadoo said:

The muffler i bought was the Areo 3030XL, i live in the easy bay in ca, so i had Steve from West Coast mufflers install it. He will do motorhomes on Saturdays only.

as for the old muffler it was leaking an when he pulled it off it had something loose inside, an call me nuts but i can swear the motorhome is smoother to accelerate an the engine runs smother🤪

You necked down your exhaust to 3"???

[Gary Cole]

I've been thinking about going to a 5" exhaust from the turbo with a free flow muffler.  That short elbow looks very restrictive. Pittsburg Power has a good website with a lot of information about how opening up the intake and exhaust on newer smog diesels can have substantial benefits including horsepower increase ,reduced turbo heat, and lower top engine heat. They specialize in upgrading new trucks with better systems. Our RV's certainly need help there. No one wasted any money on the air intake or exhaust system.  The resulting increase in turbo boost from a freer flowing system also decreases engine heat. I  did not know that until I started researching their website. Seems counter intuitive. They have been around for a very long time. They made their reputation tuning older mechanical injector diesels such as the 855 NT Cummins to produce a reliable 780 hp to the ground. Owner operators loved them. 

Edited May 9, 2023 by Gary Cole

[klcdenver]

The top left is the tailpipe. I used stainless flex from the turbo down to the piece in front of the muffler with clamps. You will need to build a hanger where the old muffler was to support the new system. You will also be about 30 pounds lighter with a setup like this. I can take this off in about 5 minutes and gives you a lot off access to get that side and rear of engine also.

[Paul J A]

https://www.dynaflexproducts.com/  You will love this Co. 

On 5/8/2023 at 10:29 PM, Gary Cole said:

I've been thinking about going to a 5" exhaust from the turbo with a free flow muffler.  That short elbow looks very restrictive. Pittsburg Power has a good website with a lot of information about how opening up the intake and exhaust on newer smog diesels can have substantial benefits including horsepower increase ,reduced turbo heat, and lower top engine heat. They specialize in upgrading new trucks with better systems. Our RV's certainly need help there. No one wasted any money on the air intake or exhaust system.  The resulting increase in turbo boost from a freer flowing system also decreases engine heat. I  did not know that until I started researching their website. Seems counter intuitive. They have been around for a very long time. They made their reputation tuning older mechanical injector diesels such as the 855 NT Cummins to produce a reliable 780 hp to the ground. Owner operators loved them. 

https://www.dynaflexproducts.com/ 

[Gary Cole]

Paul those trucks are light years distant from the 1949 LJ Mack which I learned to drive on the farm. Two stick 10 speed, clutch so heavy it pushed a skinny kid like me out of the seat, power steering was huge steering wheel with a spinner, heater was straight exhaust pipe 1" from thick steel firewall, wooden dip stick for fuel gauge, 180 HP and black smoke into the next county, 50 mph downhill.  

Edited May 12, 2023 by Gary Cole

[Bill R]

Update:  I applied the JB Weld Extreme Heat to the joint and it let it dry for 24 hrs.  Started engine and the heat of the exhaust manifold bubbled the JB Weld a bit, but has stopped the leak.  The true test will be after I take my next trip and put some extended miles and heat on the system.  Will report back those results when that happens.

 

[dl_racing427]

Obviously not an extreme heat application, but many years ago my late Dad had a boat with an OMC stern drive, that had water jacketed log style manifolds.
I always helped him winterize it, but one year after the final flushing and fogging the motor, we failed to drain the manifolds.
Started it up the next spring on the hose, and water was spraying everywhere. 🥵

After kicking ourselves, we pulled the manifolds and ground out the cracks, drilling small holes at the end of each.
After cleaning it well we packed them with JB Weld.  Sanded it smooth and painted, and at a glance you wouldn't even know it was done.
We used that boat several more years, and after trading it on a newer model, the local Fire and Rescue squad bought it for a water rescue boat.
I saw it on the lake for several more years.
Done properly, JB Weld is some good stuff.

Good luck with your repair, hope you have as good a result as we did.