December 18, 2020 at 2:03 pm #13476
Tony Athens, a Cummins marine engine guru, has stated that exhaust system and aftercooler issues have killed more of these engines than all other causes combined. I thought what with it being winter, Covid, etc. now would be a good time to address some important items.
If your engine still has the “stock” white double jacketed exhaust elbow, you are on “borrowed time”. As Tony refers to these “doomed to fail” elbows (all exhaust elbows eventually fail, but if these fail you could be sending water into your turbo and even your engine) when they fail (and maybe before) they can cause very costly damage (maybe the need for a new engine). See the photo showing the white elbow for an example of these elbows with the poor setup. To remedy the problem, you will have to get a “custom” dry exhaust elbow made. We had ours made by Scott at National Marine Exhaust in Marysville, Wa., but there are other options like Tony at Seaboard Marine in Southern Cal. With the custom elbow, when it fails (10++ years), water cannot run uphill to get into the turbo avoiding the need for major repairs. Gravity can be a wonderful thing. 🙂 See photo of my current exhaust.
Aftercoolers require regular servicing or replacement before normally required. Properly serviced aftercoolers can operate for many years and thousands of hours (10,000 plus). A new aftercooler costs about $3400 US just for the part. Even a brand new one, unless purchased from Seaboard Marine, should be taken apart and “greased up” following Tony Athens’ protocol. The same protocol (shown under Tony’s Tips on his website sbmar.com) is used when conducting routine maintenance on these. The reason for this is the fact that you have several dissimilar metals in close contact all within an electolyte (salt water) with only a small “o” ring keeping the seawater out of your engine air intake. The grease helps to keep corrosion under control by providing a barrier between all of the various metals. The aftercooler core needs regular cleaning by being removed from the engine so both the air side and the water side can be adequately cleaned. Just flushing with products like “Barnacle Buster” do not do the complete job! While BB will help remove calcium buildup and clean the water passages, it does nothing for the air side nor the corrosion issues. The air side gets “gummed up” with an oily residue over time due to the CCV (Air Sep) system recycling oily air from the engine back into the air intake eventually “air starving” the engine if left long enough. Plus, as outlined in Tony’s protocols, the aftercooler should be pressure tested to ensure no leaks as an essential part of the regular servicing (we don’t want salt water entering our engines, right.). Tony has a complete video under Tony’s Tips on his website on how to service your aftercooler. I did my own, and it is not that hard to do. I figure I saved over $500 labour.
Disclaimer: I have no affiliation with Tony Athens, Seaboard Marine, or National Marine Exhaust. I am just a satisfied customer of each, and am thankful that Tony provides tons of free info on his site regarding marine engines (especially Cummins).December 18, 2020 at 2:13 pm #13477
Here are the photos from above post (I hope):
Pilitak NT 37-068December 18, 2020 at 2:28 pm #13478
Sorry for the multiple posts, these could have been combined. Under normal conditions, aftercoolers should be serviced by removing them from the engine for bench servicing (removal only takes about 15 minutes) and a complete “tear down” every 2-3 years. If you freshwater flush your engine regularly and store it over the winter that way (assuming you don’t just keep using it), you can increase the time frame to 3-4, maybe 5 years (according to what I saw from Tony’s info). Conditions can vary, and a conservative approach is best (monitoring both corrosion and “gunk” buildup on the air side) until you can determine what is best for your situation. Most mechanics if left to their own methods, do not adequately grease the aftercooler parts. Neither does Cummins. Monitor them, or at least ask them to follow the protocol. It only takes a couple of minutes longer to add the “extra” grease.
TomJanuary 18, 2021 at 9:01 am #13508CarmenParticipant
I recently purchased my NT32 with a 6BT (no after cooler) 220hp Cummins. The survey indicated pinhole leaks in the exhaust elbow and muffler and recommends replacing both. I have been reading several articles related to this and trying to decide how to proceed. My elbow turns down 45 degrees at the exit of the turbocharger. I need to remove it to inspect the impeller but I’m thinking I can replace like for like and not get into a vertical loop arrangement. I intend to ask Scott if he can take a look as they manufactured the elbow in place to see if they are doing anything different on an arrangement like mine. I did read an article on SENTOA about how spots after the elbow and inadequate water flow and mixing but I’m don’t think I have that going on.
I’m posting this to follow up on Toms maintenance post to ask if anyone with a 6BT has modified their exhaust configuration.
BobJanuary 18, 2021 at 9:02 am #13509CarmenParticipant
Here’s another viewpoint.January 20, 2021 at 2:29 pm #13511
Good idea asking Scott at National Marine for his opinion. I would also suggest posting photos with questions regarding your exhaust on Tony Athen’s website (sbmar.com) in the Cummins forum area. You will need in addition to the above photos, a photo showing where the water is injected into the white elbow. Due to your layout (batteries and water lift muffler being close by) it may be difficult to obtain a good photo, but do the best you can. If that set up is what I think it may be, you are not immune from potential problems, but not in as bad a position as the one shown in the earlier photo I posted (showing the setup in the early NT 37’s).
There are photos on Tony’s site under Tony’s Tips, showing what the inside (exhaust side) of your turbo should look like and what it will look like if it has been ingesting saltwater. Taking off the elbow will allow this inspection. If you are replacing the elbow anyway, best to get it “right” this time. Between Scott and Tony you will get it figured out.
TomFebruary 5, 2021 at 12:39 pm #13537Gary WhiteParticipant
Carole and I have a 04’ Nordic Tug 37. I started hearing stories of this riser failure being an issue several years ago and had been considering changing it then. To my knowledge it is original to the boat. After reading Tom’s story I decided to go ahead and do it this year since we are not cruising as much and Carole just had a partial knee replacement. I’m having a national diesel exhaust brand riser installed. The standard riser though is too high for our application so Scott from national exhaust had to come and measure for the clearances necessary to install it in our boat. Although I had replaced and or rebuilt our exchanger and after cooler in 2016 I also took them apart and inspected them. The heat exchanger looked fine but the aftercooler needed some cleaning out and attention. All that aluminum I guess is a little more susceptible to the corrosion.
Once we get the installation completed I’ll repost with some pictures and more information. Thanks Tom for encouraging me through your posts to move forward with this. I do know that the hose between the muffler and the riser was starting to weep salt water thus likely beginning the eventual failure process.
Lash SplashFebruary 5, 2021 at 3:58 pm #13539
Your welcome Gary. It is always best to be preventative with these things!!! If left too long, it could get very, very expensive, and as we all know, when it leads to a breakdown, it WILL occur at the worst possible location and time.
I am not some sort of a guru, but I do like to learn and do quite a bit of research. I have learned a lot, and “tips” from others have saved me much heartache and expense. If I can help even one other person, then it is worth it to me.
Pilitak NT 37-068February 24, 2021 at 3:54 pm #13639Gary WhiteParticipant
We finished with the new exhaust riser installation on Last Splash. Because our fridge cutout intruded into the engine space we have a shorter elbow. It still gives us more height from the waterline so backwash will not be an issue. Our boat is heavy in the water with the dinghy and crane up top so we sit lower than some. Our original riser looks the same as in Tom’s picture above.
Picture #1 shows the inside of the rubber hose from the riser to the muffler. As I suspected there had been a crack from the inside causing salt weeping between the laminate layers. You can see the crack at the bottom of the hose.. looks like a smile. ( NOT funny though! ) This may have occurred due to an overheat issue prior to our ownership.. I have an overheat indicator installed to prevent that from occurring again.
Pic #2 Shows the delamination between layers. Note that this was not visible from the outside. This was only visible because we cut the hose in half to remove it.
Pic #3 Shows the corrosion around the outflow side of the riser.
Pic #4 Shows the finished installation with the insulation blanket on.
Although this work resulted in a couple of “boat units” to complete, it gives us security knowing that we won’t have a major failure (which was on the way with the delamination). Having the hose fail could fill the bilge with water while underway! Also the higher elbow prevents water from backwashing in from the exhaust in heavy seas. That could result in water entering the turbo which would destroy it and possibly the engine. A big thanks goes out to Tom Easterbrook for motivating me to follow-up with this project. Our Tug is 16 years young but it was time to check on some things that often get overlooked!
Last Splash NT-37 102August 22, 2021 at 6:14 am #140664palmerParticipant
Thank you for the great explanation and detailed pics.
I am trying to locate the article from Seaboard marine about misalignment of the serpentine belt on the Cummins 6B series. I have replaced everything that that belt rides on and it still is jumping and then eating the outside of the belt.August 22, 2021 at 8:46 am #14067
If I were having that issue, I would post a detailed question with lots of good photos on Tony’s forum (sbmar.com) and/or phone them for advice. It could be the belt tensioner?? I did replace the idler pulley as a preventative measure, as they have been known to fail (due to an undersized bolt) with said failure causing overheating often resulting in engine failure.
Luckily we never had any belt issues with our engine.
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