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Old 07-25-2019, 07:46 PM   #1
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Cummins 350, ISC leaking manifold

My exhaust manifold/gasket is leaking. Cummins is telling me $2,500 which includes a new manifold. Another shop is telling me 6-8 hours labor using a third party double thick gasket that they have fixed the know problem this way. Does anyone have experience fixing it this way? Obviously the second option would be at least half the price. Thanks
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Old 07-25-2019, 07:56 PM   #2
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The "double" thick gasket will be a crap shoot. It might work or after a while it could start leaking.

The exhaust manifold is a problem on the 350 ISC's. Mine cracked so I replaced it myself. Cost of the parts was ~$650 about 4 years ago.

I assume you exhaust manifold is warped. You might consider taking it to a machine shop and having it trued up. I had to do this with a manifold on a 460 engine and then replaced the gaskets. It held for as long as I had the Class C motorhome.
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Old 07-25-2019, 08:12 PM   #3
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I owned an 03 Dutchstar with an ISC 350 that had a cracked exhaust manifold.

These engines have a reputation for exhaust manifold issues.
If this were mine I would replace the manifold with a new assembly and be done with it.
The new castings from Cummins are a better design and not as prone to failure. Band aid repairs may be less money in the beginning but when you have to add that on top of doing it the right way, it amounts to more money in the end.
Just my opinion as a licensed mechanic but the final decision is entirely up to you.
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Old 07-25-2019, 08:38 PM   #4
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Our ISC350 had a manifold crack. You can get the parts from Cummins (with Cummins Power Club discount of 10%), and find a diesel mechanic to replace it. That could save you a good sum.
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Old 07-25-2019, 10:42 PM   #5
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The new manifolds are a 2 piece afair. If you replace one, replace the other one also. When I had it done, the manifolds were, I think $600 and labor was the same. Lucked out with no seized bolts.
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Old 07-25-2019, 11:20 PM   #6
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Our ISC350 had a manifold crack. You can get the parts from Cummins (with Cummins Power Club discount of 10%), and find a diesel mechanic to replace it. That could save you a good sum.
Mine is cracked too. Is it as simple as unbolting (if they don't break), new gasket, bolt on a new manifold? I was thinking of looking for a independent mechanic vs. going to Cummins but haven't decided which way to go. I'd honestly like to change it out myself but haven't thought through what could go wrong.
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Old 07-26-2019, 09:18 AM   #7
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I had an exhaust manifold that leaked and was warped on my Dutch Star (400 ISL Cummins). I had it replaced(one side only), about 4 years ago in Denver at a Cummins dealer. Cost me $1500 total. No problems after that
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Old 07-26-2019, 09:34 AM   #8
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Mine is cracked too. Is it as simple as unbolting (if they don't break), new gasket, bolt on a new manifold? I was thinking of looking for a independent mechanic vs. going to Cummins but haven't decided which way to go. I'd honestly like to change it out myself but haven't thought through what could go wrong.
Pretty much unbolting and bolting, except you'd need to remove the big air intake pipe first. When you get the new parts (a gasket and two sections of the manifolds), better buy a set of new bolts.
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Old 07-26-2019, 11:28 AM   #9
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The new manifolds are a 2 piece afair. If you replace one, replace the other one also. When I had it done, the manifolds were, I think $600 and labor was the same. Lucked out with no seized bolts.
Always learn something new reading this forums! Our ISL, built in Sept of 2003 (And was serial number wise one of the last 60 CAPS era ISL's built before shift to Common Rail and Variable Geometry Turbo ISL's), had a Two Piece Exhaust manifold as OEM.

I believe the ISC, which the ISL is based off of, had a long product run. With the block itself preceding the newer electronics that made it the ISC vs the 8.3 Mechanical. Did the early ISC's have 'one piece' manifolds?

And frankly, since the ISL's also seem to still get cracked/warped exhaust manifolds even with the 'two piece' - not sure it's something I'd consider new and improved...

IMO, Cummins knew the Exhaust Manifolds were not up to long life, and have never redesigned them for a pure 'parts replacement and hopefully labor too' revenue stream. No excuse to not CPI and have improved replacement Exhaust Manifolds for their ISC's and ISL's.

And as luck would have it, I still have never found a company that made an improved After Market Exhaust Manifold for the ISL. To me, this would be good revenue product for a company like PDI or Pittsburg Diesel, etc... I believe many owner's would pay more for a better alloy constructed, and hopefully even better ported/polished, replacement Exhaust Manifold. (Well, I know I would have...)

I've told my wife that it will not be 'if' but 'when' we need to go in for another replacement exhaust...

And yes, proper cooling down periods can help on this, and I do believe I follow those techniques. And since I was pulling a pretty good grade going from Bishop to Reno on 395 with outside temps in the low 100's when ours exhaust cracked (Could hear the noise difference from the engine immediately, and yep it was # 3 that cracked.) - cooling down had nothing to do with it. We running the engine with coolant temps maybe 2-3 degrees (Silverleaf) higher then normal. I've since added a VGT gauge to my dash, to monitor exhaust heats vs coolant temps... Stock engine, but possible it was working a bit too hard on that pull, and the exhaust temps climbed too high... So I now drive more by VGT, then by Coolant Temps... And sure, practice good manual down shifting to keep the RPM's in the happy range...

After Market companies are missing an opportunity, by not targeting the ISL and even ISC - as just a few million of them are running in Medium Weight trucks and RV's!

Best to all, travel safe,
Smitty
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Old 07-26-2019, 03:48 PM   #10
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Smitty,

I love reading your posts. You communicate well and have incredible knowledge. Thanks for your reply.


I have a one piece, I assume OEM. The shop who spotted the problem when I was passing through, Little's Diesel Service, in Knab UT, said (the owner Mike), there was a 3rd party that has a better replacement gasket and there was a 3rd party who made a 2 piece which he would recommend if I replaced it. Then a friend in Rocky Mountain Country Coaches who is a retired airplane mechanic thought there was a blow-proof gasket made with copper. I will be going back there to have them do the work I think. At this point I will probably bite the bullet and put on a new 2 piece.

By the way, I would recommend Littles and a stay in Kanab. Beautiful country close to about 5 southern UT national parks as well as the Grand Canyon. I love the small towns this life style allows us to experience.


Thanks to every else for your input. Not sure what I will do but right now I am going to start spraying with penetrating oil.
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