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Old 07-22-2015, 05:09 PM   #1
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ISL370 Exhaust Manifold Gasket Leak

Looking for some input, not on 'if' as it will need to be done. But on 'timing of when', to replace the exhaust gasket. Probably will need the exhaust manifold machined, or if cracked - replaced.

This is a 2003 ISL370 CAPS era engine.

Here is what happened, and where I think I am now:

1) From Lee Vining, CA to Sparks, NV my wife and I both heard a new sound for the first time. We were climbing a pretty good grade, and between 2150-2300 RPM, when were heard what we thought was a rattle sound from the rear of the coach.

2) I checked for loose fittings, clamps, etc. but could identify nothing.

3) We did have two compressions fittings loosen up, and lost about 2 gallons of coolant. (The compression fittings could have been loose before Lee Vining, and due to parking on dirt I never noticed the slight dripping. We found this at Sparks, NV, due to drips on the asphalt where we were parked.) The best I could tell, the coolant resevior still had coolant remaining at the bottom of the tank. But the eye glass was for sure dry, and I'm guessing due to only adding 2 gallons of coolant to the reservoir, that it was not completely emptied. Engine temps all remained normal, and no lights or Silverleaf error codes. And now we also know, no ECM errors, as we had that checked today.

All of that background, to finally come around to my opinion that we did not run the engine with any shortage of coolant.

4) While inspecting for the leaking coolant, I crawled under and shine a strong light on every part of the engine that I could see. Including inspecting for a cracked exhaust manifold. All looked good on the exhaust side of the engine. And, from the angel I could see, I did not detect any signs of escaping exhaust marring the block anywhere.

5) After finding and tightening the compression nuts that were allowing the slow leakage of coolant. We completed our stay in Sparks, NV and then headed East across Nevada. Many stops along the way, and regular checking for coolant leakage. All was good. But, one compression nut up above high on the block and out of line of sight, I could only get two minor bites on the nut, and just enough tightening to stop the leakage for now. (None of my tools would work, and I did purchase a few new ones to get even that little bit of snugging up on that compression nut.)

6) We were in Richfield, UT for a few days. And I noticed a Cummins sign an a business called Jay's Diesel Service. I asked the owner of the campground his thoughts on the place, and he said he referred people to Jay's all the time. I stopped in, explained to Jay that I wanted to have someone with the proper tools snug up a compression nut that I could not get too. And also hook up to Insite to see if we had any ECM codes recorded. Said I was leaving to go East in two days, and could I stop by when he opened and get out on the road early. He said no problem, except that his Insite gent did not come into about 8:00AM.

Today we pulled into Jay's at 7:45AM. He was out front talking with a mechanic. When I stepped out of the RV, he said 'You have an exhaust leak.' Then asked me to remind him what it was that I needed done. He had his mechanic get going on the getting up and into the compression nut. (Was glad to see he had to go to his tool box four times, trying a different tool each time - before he got a good bite and solid tightening of this compression nut. Made me feel a bit less incompetent!) While he as doing this, Jay crawled under and stood up behind the engine, and looked the exhaust manifold over well. No cracks that he could see, but he said he could see the sign of gasket leakage around number 3. All bolts looked to be in place.


OK, so now I'm looking for input.

1) How far do you feel I can drive with a leaking exhaust manifold gasket? For now, not leaking much, but it is leaking.

2) Can I go a couple of thousand miles, I'd like to continue my travel for a few weeks, going into Denver area with rough climbs ahead on I70 East, then again I70 West. Probably a total of under a 1000 miles. I'd return to Jay's, and have them replace the exhaust manifold gasket. If the exhaust manifold is not cracked, have them machine the surface if it's warped. Or, replace if cracked.

I've driven two cars with Slant 6 225's in them, for several months with leaking exhaust manifolds. (Of course, I was a teenager with one of them. And the on the second one it was a 20 mile round trip drive to work vehicle. I believe the risks are that the leakage gets worse, possibly cracking the exhaust manifold. And, if the leakage gets worse, then I have the risk of the wrong item heating up, melting of wires, possibly risking a fire too.

But, if I monitor it closely. Observe no worsening of condition - what do you think about driving it for a max of another 1000 miles before addressing.

I don't want to do something stupid. But do know of one gent with an ISC that was in Fairbanks, AK when he found he had a leaking exhaust manifold gasket. He said he was going to keep going, and replace the gasket, and check the manifold when he got home to Montana. And, from emails I received trading pictures, that is exactly how it worked out for him.

So sorry for being long winded, but was trying to provide coolant leak background (Odd that I got the ruptured exhaust manifold gasket at the same time that I lost 2 gallons of coolant.). And for now, identify this as a what the mechanic, Jay, stayed was a minor exhaust gasket leak on #3.

Opinions on if it's OK to press on for a bit - safely! (Again, with daily monitoring for worsening condition...)

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Old 07-22-2015, 05:30 PM   #2
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Yeah, me again - I know you missed my crisp posts!

Jay, the owner and hand's on mechanic from the shop, just called to ask how everything had gone on our days drive. Mostly checking on the compression nut, as he wanted to be sure we had remained dry after his mechanic had tightened this up.

We talked some more about he gasket leak. He said from what he could see, no cracks, not lost or broken bolts. That the felt we should just loosen the exhaust manifold, check to be sure it was not warped and inspect it real good for cracks, and then install a new manifold gasket and retighten everything back up. (Of course, if we saw other problems with the exhaust manifold, we'd need to decide what to do then. Machine it, replace it, etc.

What do you thing the chances are of the manifold itself still being OK, and only needing a gasket?

TIA, again,
07 Country Coach Magna Rembrandt 45' ISX600
Roo II was our 04 Country Coach Allure 40'
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Old 07-22-2015, 06:41 PM   #3
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Yes, I did miss your crisp posts

I would be surprised if you get by with just a gasket. The leak itself my cut a groove making it harder to seal. You might get lucky though.

I have a GMC suburban, about 8 years ago I noticed a slight exhaust leak, took me a while but I found a used exhaust manifold (1989 with +200k miles on it). When I took the old one out it fell into 3-4 pieces.

I also had an exhaust leak on a Ford 460, I got by with just replacing the gasket.

Good Luck
Jim J
2002 Monaco Windsor 38 PKD Cummins ISC 350 8.3L
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Old 07-24-2015, 07:49 AM   #4
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There is a new improved gasket in the Cummins inventory that they will use. Do a search in this section for ISL exhaust leak you will find a long thread. Start soaking all the bolts.

Mine I was able to just slide the manifold back a little and replace all the gaskets....60K ago and still holding fine. Sounds like you found a good shop.

Start soaking now...broken bolts are $$$$.
Happy Trails,
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Old 07-24-2015, 08:31 AM   #5
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Having replaced two exhaust manifolds on two difference ISC engines. Both manifolds were warped badly and needed to be replaced. Shortcuts usually don't last long.
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Old 07-24-2015, 11:34 AM   #6
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Closing the loop back that the exhaust bolts were not loose. They were tight as they should be.

Going to cautiously move East next week into the Denver area. Looking for input on good repair shops in that region. Will call and make an appointment, give them our engine SN, and confirm they have the exhaust manifold available and ready before we start the work. (A shop here in Grand Rapids, commented that they had recently waited several days to get an exhaust manifold for a ISC. Don't want to be sitting in a 'shop resort' for a few days waiting for parts!.

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