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Old 05-29-2018, 03:14 PM   #1
City: Cedaredge
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Detroit 6BT-5.9 Diesel

Wondering if anyone has had experience with the Detroit 6BT-5.9 engine?
I know people who have Detroit engines and have had pretty good luck
with them. But no knowledge of the turbo marine ones. Appreciate
any comments.

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Old 05-29-2018, 03:40 PM   #2
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Detroit doesn't make a 6BT-5.9 engine..

on the other hand..

Cummins does make a 6BT-5.9 engine.. and it can be a very good engine...depending on the HP rating and previous maintenance.

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Old 05-29-2018, 03:59 PM   #3
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As far as I know a 6BT-5.9 is a Cummings engine. Cummings makes good engines. That engine is a light to medium duty engine. Meaning it can't be run at rated hp for more than 2-6 hours in a 12 hour period. The issue is heat build in the cylinder/head parts. Even at reduced speeds, turbo engines wear faster than non turbo. While a turbo increases engine efficiency, it creates higher temps in the cylinder and head, wearing parts faster. But today almost all new engines have turbos. The reason as I see it it to have a smaller engine and more hp in most sailboats and smaller yachts. New non turbo engines are hard to find.
My Detroit 671 naturals (non-turbo) engines are 70 years old, are heavy duty and can be run at full hp 24/7 and I do cruise like that. You find them rarely in boats built after about 1995. I rebuilt them for their 1st time a few years ago. But I won't have to do it again, nor the owner after me or the one after him, and so on.
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Old 05-29-2018, 03:59 PM   #4
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Thanks for the reply! Guess that is why I couldn't find any info. Will check further
and see what I can find out about the engine.
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Old 05-29-2018, 04:10 PM   #5
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Cummins 6BT. Used everywhere, Dodge trucks, motorhomes------even boats.
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Old 05-29-2018, 04:54 PM   #6
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Originally Posted by Lepke View Post
As far as I know a 6BT-5.9 is a Cummings engine. Cummings makes good engines. That engine is a light to medium duty engine. Meaning it can't be run at rated hp for more than 2-6 hours in a 12 hour period.

Not to split hairs here; close, but not exactly so. The Cummins (no "G" in Cummins) 6BT is made in a range of configurations, among which you'll find continuous, heavy duty, government service, medium continuous, intermittent, high output ratings.

The 180HP 6BT in my boat is rated at medium continuous. That rating limits full power to 6 hours out of every 12 hours of operation where the reduced power is at least 200 rpm below the rated full power rpm, and intended for use accumulating 3000 or less hours annually. Perfect for a trawler. 6BT's with a continuous rating are used where uninterrupted and unlimited service at full power is required. The serial number on a Cummins tells the story, a dealer can tell you anything you need to know about that engine based on that number.

Tony Athens is the go-to guy for Cummins Marine, he knows his Cummins line. Lots of info on his website.

As far as reliability, the Cummins enjoys a reputation for longevity, repairable, and trouble-free if cared for. Mine is at 7000 hrs. uses no oil, no smoke, and efficient. It's a turbo, but has no seawater exchanger (keel cooled) and no aftercooler. Fully mechanical. Less is more.
If you want technical information on things diesel, check out
Steve Sipe
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Old 05-29-2018, 05:20 PM   #7
City: Cedaredge
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Thank you Steve. Looking at a Cheer Man 38 with 2 of the 6BT-5.9 engines. I think
they have between 4000 to 5000 hours. They look well kept. But will get the serial
numbers and try to check the out that way. Probably go look over the vessel sometime
in the next few days. Thanks again for the info!
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Old 05-29-2018, 08:48 PM   #8
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Had a 6BT-5.9 210 HP in my charter boat till switching to a 300 C for more HP / speed. Ran the B @ 2,400 for hours on end, maybe 100 trips per year. Rock sold at that HP.

Have a 6BT-5.9 220 HP in my Dodge pickup. It has 447,000 miles (9,000 +/- hours) on it. Never been inside the engine except to check valve adjustment. Hope the truck lasts as long as the engine.

I'm tired of fast moves, I've got a slow groove, on my mind.....
I want to spend some time, Not come and go in a heated rush.....
"Slow Hand" by The Pointer Sisters
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Old 05-29-2018, 09:07 PM   #9
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Thank you Ted!. By the way, you have a cool boat. I like what I am hearing about

the Cummings. Want to hang out in the Bahamas, so do not need a lot of extra

speed or power.

Take care and thanks

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Old 05-29-2018, 10:01 PM   #10
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The CUMMINS 6BTA are a great engine. We had twin 370hp 6BTA's in our last boat and loved them. Take Steve's advice and have a look at Tony Athens web site . Some good technical articles about the 6BTA and general advice like marine age on engines and advantages of running at low power setting,

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Old 06-01-2018, 07:08 AM   #11
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Almost anything branded or made by Cummins(sorry for bold just been misspelled a few times) is top notch.

The old ram's with the 12 and 24 valve cummins 5.9 engines are doing 500k miles and hold their value very well. They also get "turned up" to make more power in trucks and at the drag strip can hurt some feelings. My neighbor has a 99 Ram with a 5.9 cummins 12v with over 500hp and has been ran that way for years without fault.

Of course you'd be a fool to turn up one in your boat with the demand for constant power but still is worth knowing.

Doesn't hurt that they have the most reasonable asking price for parts and sources worldwide.
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Old 06-01-2018, 07:34 AM   #12
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Old 06-01-2018, 08:34 AM   #13
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Cummins is an interesting company. All they make is engines (and supporting systems). Other companies make engines AND make tractors, cars, bulldozers, etc as their primary products. As an aside they might sell some engines.

When your only product is engines, you better make good engines!! And for the most part, they do.

Founded by Clessie Cummins, an Indiana bicycle mechanic, around 1920, with help from a banker friend. Purpose was to refine the diesel engine. Developed his own Pressure-Time (PT) injection system. Was not super successful in the market until after WW2 where the N series started to be adopted by heavy trucks. Sales took off and the N series held big market share from the 50's well into the 90's. That success financed development of several other series which include the B, C, L and M popular in our size boats.

Cat was their big competition on road tractor engines, but like ten years ago they seem to have been caught flat footed when emission regs got tight. I think they got into a "patent pickle" of some sort and withdrew completely from the market. Cummins pretty much owns the road tractor engine market in the US now, although there are some viable competitors.

They make much larger engines (K series, 19 to 95liter) but those are not really appropriate for the go-fast sportfish market dominated by Cat, MTU and MAN. Cummins in that HP class are too big and heavy for the zippy boats. But the commercial marine market are happy with the Cummins machines where weight is not a big deal.

If anyone has run an old N series in a boat (mostly 14liter, 200-400hp) you know what a delightful machine that is. So smooth and quiet for a diesel, especially if you ever spent time around Detroit two strokes!!!

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