Replace Exhaust Manifold Gaskets 8.3 Cummins Diesel

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We got up one morning in mid-May planning to change the oil on our 2006 Holiday Rambler Ambassador 40PLQ Cummins diesel ISC 8.3 liter with approximately 60,000 miles on the odometer. The oil change was halted when Athena opened the floor access to the engine and found black on the exhaust port of Cylinder number 4. When we found the leak, we needed to find out the repercussions of this would be, and what it would take to repair it. Cummins rep told us the engine would not be harmed if we completed the next portion of our journey of 450 miles. In fact, they said the biggest issue we would experience would be exhaust in the house, and power degradation. Others we spoke to said oxygen would gain entry into the valves on any cylinder with a blown gasket causing heat buildup and total destruction of the cylinder head. That my friends will get real expensive, real fast. I would guess about $7,000 for the rebuilt head and $2000.00 for a rebuilt manifold. When we landed in Florence, Oregon this project became our first order of business.

Getting the bolts off is the first task, but if you break one, you are in for big dollars and a real hassle to find a machinist who will come to your location and drill it out. Don’t break the Bolts! We took a drive out to Cummins in Coburg, Oregon. I was sure that I would have them do this repair and use our Good Sam Extended Service Contract to pay for it. Turns out Cummins will file the claim with Good Sam, but I would have to get Good Sam to pay me the money as a reimbursement. So I would have to front the cash to Cummins, then beg Good Sam to pay me back, that would be OK, but I did not have the $1,700 they needed to start the job. The Cummins shop has quite a deal going. If we let them do the work they would replace the Manifold, replace the exhaust, turbo gaskets with new ones, and replace the spacers. The $1700.00 included drilling three broken bolts. Three bolts, is about the average number of bolts they break on this job. If they break additional bolts, we pay the shop time for drilling those bolts. This is over and above the $1,700 estimate. If they screw up the cylinder head, we buy a new loaded head and pay them to put that in too. The job could climb as high as $10,000. For that kind of money, I would rather just park the thing, and live in it until the roof caves in around us.

Fortunately, the Cummins rep knew we did not have the resources to absorb that kind of deal, so he sold us the parts, and made sure we understood how to minimize the chances of breaking a bolt, and how to get the thing back together again. So, will share what we learned here. The following image is a picture of the 4th Cylinder exhaust all covered in soot.

The Cummins guy told me to drench the bolts in penetrating oil. Then, at the end of a few days start the engine, get it hot, then turn it off and spray it again, and remove the bolts.

I decided to use the Jericho approach as described in the Bible. The army marched around the city for seven days, and on the seventh day the walls came tumbling down. I opened the hood and sprayed all the bolts and the turbo bolts down. I did this roughly every 12 hours 7 times. Each day I put a ½” socket on the bolts and gave it a pull with just my arm strength. The last time I tried it, the bolts broke loose and spun right out. If you can avoid it, don’t heat the engine up. As you can see from the next picture you kind of have to cozy up to the engine. A hot engine will cause nasty burns. The exhaust is the hottest region in the engine. While waiting days for the oil to do its work, you need the following parts, and I would recommend going to a Cummins dealer to get them. I searched high and low. Cummins was the cheapest, and most willing to give us advice on doing the project right. When you go, bring your serial number, this assures you get the right parts. Amazon has many of these parts, but they do not match them at the serial number detail. Our block is the Pegasus block which is different than other 2006 blocks, so it does matter.

Here is the list:

  • 6 – $60.12 – pn-5269779 Manifold Gaskets
  • 12 – $39.12 – pn-3944593 Manifold Bolts
  • 1 – $243.73 – pn-3967751 Manifold Exhaust Cylinder 1 and 2. (Only needed if manifold cracked, Badly Warped, or you have the old one piece manifold still)
  • 1 – $110.17 – pn-3901356 Manifold Exhaust Cylinder 3 and 6. (Only needed if manifold cracked, Badly Warped, or you have the old one piece manifold still)
  • 4 – $17.08 – pn-3818823 Turbo stud (expect to break these when the turbo comes off.)
  • 4 – $10.56 – pn-3818824 Turbo nuts (Don’t reuse the old one, heat kills them)
  • 1 – $5.24 – pn-3901356 Turbo to manifold gasket
  • 1 – $3.35 – pn-5264569 Turbo oil drain gasket

Total Parts came to 489.37 to do with a new manifold. Without the manifold which we elected came to $135.36. They will do the job at a base cost of $1300.00 for labor plus parts provided everything goes well. The cost goes up if bolts break or other issues are found.

Here is a video that helps put the job into perspective. This engine is the next size up, but the process is the same.

The bottom bolt on cylinder one, the port closet to the rear of a diesel pusher is one heck of a nasty one to get at. Athena took five hours figuring a way to remove this bolt. The air conditioner pump, and the thermostat hose are in the way. The combination of tools that save the day was a low profile 3/8″ ratchet and a swivel impact socket. The swivel assembly made it so the socket was long enough to barely clear the exhaust manifold, but not so long that the air conditioner pump would block the ratchet. The picture above shows just how tight this area is. If we were in a place where we could be indefinitely, and we had a shop, I would have had her pull the thermostat housing. We could not afford to leak antifreeze in this location, so we worked around it. The wrenches below, saved our bacon on Cylinder 1. If you see no wrenches, we need to be white listed in your ad blocker.

The square section at the bottom of the above photo is where the turbo connects to the Manifold. We decided to leave the turbo on, in order to reduce work, and not discover new problems. This posed a challenge though for getting the bottom manifold bolts off. The bolt on the right was loosened with a half inch drive, and a ½” deep socket, and removed with a half inch off set end wrench. The bolt on the left used a 3/8″ ratchet, a half in deep socket on a swivel.

We left all but one top bolt about a thread from being removed, removed all the bottom bolts. Then pried the manifold back from the cylinder head with the breaker bar. One cylinder at a time, removed the old gaskets. Once the area between the head and manifold were clear of debris, we inserted the bolt hole end of the gasket between the cylinder head and the manifold, then ran a bolt covered in anti-seize through the manifold ear and into the cylinder head, but only tight enough to grip into the cylinder head. Once the gasket was secure on the top, we let it drop, then lined up the edges of the casket with the edges of the manifold, and inserted the bottom bolt through the manifold, the gasket, and into the cylinder head. Don’t tighten the bolts until all the cylinders are done. We used the breaker bar below to break some bolts lose, and as a pry bar.

Turned out Cylinder three had the broken gasket, and was blowing soot all over cylinder 4. Turns out Cylinder 3 has a reputation with the Cummins 8.3 in diesel pushers for doing this about every 50,000 miles. The Cummins rep says not enough cool air reaches the engine. If the engine were in the front, this would not happen.

The Cummins OEM Gasket

Gasket falling into place.

Since this is a two piece manifold rather than the original one piece manifold, we decided not to pull the manifold out of the RV at this time, hoping the gasket just failed. The Manifold was not checked for warping, so there is a risk we will have to do the job again, we should know by fall. We did not do this due to a lack of a place where we could work for an extended period of time should it need machined, the RV would be out of commission until the manifold is returned. This is the downside to living in an RV full time. We shall see how it goes. 

The job with parts shopping took Athena about 14 hours to do. My job was to research parts, technique, spray the engine with oil, and add weight to the wrench now and then.

Speaking of technique, we can’t stress enough the risk involved with this job. The bolts rust, weld themselves into place over time, be careful. Here are the tips we were given.

  • Never bounce or jerk the wrench, this puts the wrong kind of force on the bolt and it may break.
  • Gently pull short 20″ or less breaker bar toward you, if the bolt feels like it is turning, turn with even force, if it stops or does not break loose, soak in oil.
  • Take your time, plan on soaking the bolts for days on end. Don’t just spray the bolts, soak the bolts. We used Sea Foam Penetrating oil and did not break any bolts.
  • If you have to, heat up the engine and spray the bolts again.
  • Patience is key!


When all the gaskets are in place, hand tighten the bolts then use the diagram below for tightening your bolts. You need to tighten them with a torque wrench to #32 to #35 pounds starting at the center of the manifold and working your way to the outer edges.

The last two tools are a torque wrench that you need to use to be sure your bolts are at the right level of tight. If over tightened, the bolts could expand and break when the the engine is running, under tightened the exhaust flange may allow the new gasket to burn. The swivel adapters came in handy in some the areas where perfectly straight just does not work.

We are happy to document our experiences and those of others to help all of us do the jobs we need to do. We are not mechanics however and only know what we did, and that it worked for us. We cannot promise that any of what we did will work for you. Please do your research, and if you have any doubts about anything please contacts a trusted mechanic. We went to great effort to get this documented correctly so you can gauge the amount of work involved in this project, we cannot guarantee that we did not forget steps or even mis-remember what we did. This information is free, and might be worth about that much. Register with Cummins for manuals and access to part numbers

Good luck with taming your exhaust…

2 Responses

  1. Chuck Utgard

    Thanks, 8.3 head replaced on 1995 Monaco Dynasty, Spokane, WA 2009 +/- (38k on clock), # 6 blew gasket and broken bolt on the road – vacation (long but still only vacation) 1,000 miles from my tool box. Exhaust brake worked…. but just a little. Left Winter stomping ground in May, and again 1,000 miles from home moving from Thousand Trails (TT) Pacific City, OR to TT Whalers Rest just outside Newport, OR; noted the exhaust brake problem again. Checked and looks like #6 again but over the years I find places we like and on heading to Seaside, OR stopped at repair shop in Tillamook, OR. Discussed problem with owner and he came back with #5 area manfold crack or blow out of gasket. Stopped at TT Seaside for a couple of weeks before taking to shop for a few days. You story/problem just gave me a bit of hope…. maybe just gasket….. manifold costs a bit more and it would be fine …. don’t even want to discuss head with 60k on it since replacement in Spokane.

    • athena

      We noticed the soot around where the exhaust was leaking. Took the photos to the Cummins shop in Coberg. They got the parts for us, along with some removal tips to protect the block. They told us how to check out the manifold for leaks. We did not notice an issue with the exhaust brake. The engine just sounded like Popeye’s boat. We were happy not to remove the manifold, as we really did not want to disturb the turbo. The job gets more complex if we look at the turbo, then might as well check the seals and bearings there too, and while we are at it rebuild it for posterity. With these machines, the fun never ends. Let us know how it goes. The manifold gaskets are probably easier than the serpentine belt. 🙂

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