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Old 03-24-2023, 08:12 AM   #1
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Cummins 6CTA 8.3

What is considered high hours for these engines.....roughly. (I acknowledge that a lot depends on usage, service and maintenance. For now, let's assume standard recreational use and normal service and maintenance).

Is 4,000 hrs high?

Are these engines rebuildable?

If so, what do you think a ballpark would be to rebuild?

What is a ballpark to repower? I'm guessing ($40-50K?)
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Old 03-24-2023, 08:23 AM   #2
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I don't think 4K is high, assuming good maintenance regime. Aftercoolers specifically need periodic service every 3 years or so, but otherwise they're generally pretty simple and straightforward.

We had something like 2900 hours on ours when we sold that boat in 2020... and they were still essentially perfect. We had a certified Cummins tech on site and I had him do a basic "everything" when we bought in 2005 (aftercooler and heat exchanger service, gear oil cooler service, new hoses, etc.). That also included a valve job, but afterwards he told me he didn't actually have to adjust anything as it turned out.

Were it me, I'd be inclined to do it that way again... and one of the boats we shopped on afterwards would have been exactly that. No worries (although we didn't get to survey cause somebody else bought that boat before I had a chance to see it).

After that, he was good at advising me when to do what... and doing it for me when it was something I reckoned too much work to do by myself. (Like lifting an aftercooler.)

They're wet-sleeved, so rebuildable in situ is overhead space allows.

No clue about rebuild or repower costs. I've read Cummins sells re-man versions with warranties, but have no direct info...

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Old 03-24-2023, 09:03 AM   #3
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With 7200 hrs on one, I would say 4000 is not high. If you want to read more about that specific engine go to Tony Adkins does a good job of discussing marine diesels and this engine in particular. From his perspective, it’s not the number of hours, it’s the type of hours. An engine run using a lot of boost to generate most of its rated horsepower generally will have a shorter service life.

In our application, the amount of time where the turbo is producing boost is measured in minutes a year out of 300 hours. We cruise at 1200-1400 rpm and boost doesn’t show on the gauge until 1800. Do the checks you indicated paying particular attention to the aftercooler as it’s design invites corrosion unless regularly serviced. That corrosion can lead to sea water in the intake, which is generally fatal.

Other things to consider are replacing the factory raw water pump with one Seaboard Marine designed, replacing all the hoses, being sure you have good fuel filtering, and disconnecting the start heating. The start heating heats the intake air if it’s below a certain temperature to help minimize smoking on start. It isn’t needed to start and in cooler temperatures always seemed to be on, unless you were operating with boost.

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Old 03-24-2023, 09:41 AM   #4
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It really depends on how they're used and maintained. You can find a fair number of them on Chesapeake Bay in watermen's boats with 10K plus hours. They're wet sleeved engines, so easily rebuildable. Cummins still offers them as new rebuilds (one used part on an otherwise new engine). They can only be put in older boats that were built before the required tier engine mandate.

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Old 03-24-2023, 10:23 AM   #5
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We have them in our boat. Great engines. I replaced the stock raw water pumps with the SMX pumps this winter. I have an aftercooler on order since I looks like they were never serviced. I will replace one and use the old two to make a new one for the second engine. As said above Tony Athens is the Cummins guru and he loves them. Just service the aftercoolers on a regular basis. Tony has a video on how to do it properly. We have about 1,500 hours on ours but I wouldnít be afraid of 4K hours.
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Old 03-25-2023, 07:07 PM   #6
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Great engines and wet sleeve cylinders, so rebuildable. Make sure to remove and service the heat exchanger and aftercooler every 2-3 years. Not a horrible job. Stay after the zincs on these as well. Switch the stock raw water pump to an SMX.

As others have said refer to the excellent resources and products from Tony Athens at

Some good you tube videos on these as well...
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Old 03-25-2023, 07:44 PM   #7
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There is a bunch of ‘ ifs ‘
Was the original installation correct?
Was it serviced properly [ records, receipts ]
Was it ever overheated?
Was it run over 80% power for long periods?
If everything checks out then 3k hours is fine. If you knew the history and it was run conservatively, 8k hours would be fine.
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