Community Forums

00MonDip · 11-08-2012, 05:40 PM

I have just replaced the exhaust manifold in my 2000 Diplomat with ISC 8.3. The reason was due to a slight leak I noticed between the exhaust flange and the head on the 3rd cylinder from the front end of the engine facing forward. (i have the 2 piece manifold).

After removing the manifold and buying new gaskets and bolts, the holes would not line up on the same cylinder during reassembly. Tried to use an expander to force it to no avail. I gave in, and just decided to get a new manifold assembly, $550.

My question is, is there anything I can do to prevent this new manifold from warping/shrinking again? Next time, should I just live with the slight leak and the blown gasket?

Harry P

DAJO · 11-08-2012, 05:56 PM

When I replaced our 8.3 manifold I made sure the joint in the manifold was lubed up good with high temp anti seize. Lubed the bolt threads and torqued to proper number. This should help the manifold grow and schrink when heated and cooled. The slight leak will not stay slight for long. We always did this on aircraft exhaust systems.

Dave

ahicks · 11-08-2012, 07:59 PM

New manifold for the gassers come new with noticeably larger/oblonged holes for the outer cylinders.

walt2137 · 11-08-2012, 08:05 PM

I can't understand why the holes would not line up if the manifold was true flat, a small leak as stated will get worse and cut a grove in either the manifold, head or both the manifold can be trued or machined flat easily but the head is a little harder to deal with. I have changed the gaskets on a ISB and a ISC and on both I sprayed both with a penetrate for a couple days before attempting to loosen the nuts with good results.

Mr_D · 11-08-2012, 08:28 PM

Quote:

Originally Posted by DAJO

When I replaced our 8.3 manifold I made sure the joint in the manifold was lubed up good with high temp anti seize. Lubed the bolt threads and torqued to proper number. This should help the manifold grow and schrink when heated and cooled. The slight leak will not stay slight for long. We always did this on aircraft exhaust systems.

Dave

Did they give you torque values for lubed threads or did you make the needed adjustment yourself?

For those that don't know: If the torque value is for dry threads and you lube them then you need to us something like 20% less torque or they're overtorqued. There are charts out there for figuring this reduction.

slickest1 · 11-08-2012, 09:09 PM

The exhaust manifold on my 8.3 cracked so I had to replace it. The new manifold (2 piece) was quite a bit heavier than the original. I wonder if the original factory installed ones were not heavy enough? I have seen a number of threads on different forums about cracked and warped manifolds. Makes me wonder.

00MonDip · 11-08-2012, 09:59 PM

Walt
I agree with you that the if the manifold came off, it should go back on. The bolts all came off ok and the manifold proved straight and true on a flat surface, but there is no doubt that the mounting holes were off on the one cylinder by about 1/8 to about 1/4 inch, preventing any hope of starting the bolt in straight. I am certain that the manifold shrunk in service, enough to distort the one flange and cause the gasket to blow out.

I am just trying to figure out how to prevent this from happening in the future. I bought the coach used and cannot vouch for how it was driven prior to my ownership. Having flown turbocharged aircraft, I am familiar with the concepts of gradual warm ups and cool downs, and have applied them to my 10K mile of driving. I am hoping now that I am starting with a new manifold, that I can treat this one better.

Harry P

sc3283 · 11-08-2012, 10:56 PM

Harry, many times the manifolds seem to shrink once removed. They do exactly as you state, come off but won't go back on. I have had Ford, Chevy, Honda, 8n tractors do the same thing. Luckily I have yet to need to worry about my 8.3c.

MotionGrantd · 11-09-2012, 09:33 AM

My ISL400 also blew the manifold gasket. It created an incredibly loud whistling sound at various rpms. I got it back from the shop yesterday with a new manifold and gaskets. It was a $1,500 repair, but was fully covered under my aftermarket warranty.

Bob (WA0MQE) · 11-11-2012, 02:13 AM

This is apparently a fairly common problem with rear diesel engines. According to Cummins they main culprit is heat. Be more aware when pulling up long steep hills that slow you down and cause engine temp. to rise.

I had the same thing happen this last summer, and it was right after a trip that took me through some pretty good mountains. Had to replace manifold.

In my case there is not enough air flow across the engine. I have a side radiator and my rear engine cover, unlike some coaches has no ventilation openings. I'm considering adding a 12volt blower with ducting and arrange the duct to blow air front to rear across the manifold area. A friend added a water sprayer system that directs water onto the side radiator. He only uses it when he's climbing long hills. Said it makes a big difference lowering engine temp.