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Old 08-27-2015, 10:01 AM   #1
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Cummins 6BTA 350HP

Anyone running these engines?

I would be interested in any feedback regarding performance, quality, maintenance, issues, positives etc.

Will be on a 44,000 pound full keel, semi displacement vessel.
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Old 08-27-2015, 10:33 AM   #2
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I have twin 370 6BTA's. I just did a tour of the local Cummings dealer's rebuild center, who explained that the only weak point, in an otherwise brilliant engine, is the aftercooler. They had a pile of them in a crate with varying degrees of deterioration. They MUST be checked and cleaned every two years. Pulling them is easy enough but cleaning them is done in a three stage pickle and then neutralized, so is best taken to a dealer.


My boat is around 35,000# and I cruise at 8.5 kts and get 3mpg, which I find pretty awesome.
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Old 08-27-2015, 10:50 AM   #3
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Not aware of a 350hp model, there was a number of models, from 210hp to 370hp, the one that you are talking about is most likely the 330hp one. Exceptionally good diesel, parts availability is excellent and on the lower cost side, in addition many service yards can easily handle. Get a good survey, oil samples and make sure it achieves max RPMS. Also truck load of info on boatdiesel dot com as well, become a member and search, well worth the cost of admission!
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Old 08-27-2015, 10:56 AM   #4
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My typo - they are 370s (my current engines are 350s!)
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Old 08-27-2015, 10:58 AM   #5
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Quote:
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My boat is around 35,000# and I cruise at 8.5 kts and get 3mpg, which I find pretty awesome.
Just to clarify: at 8.5 kts you get 3mpg or 3kpg? Or is it that you cruise at 8.5kts and use 3gph (= 2.8kpg)?
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Old 08-27-2015, 11:01 AM   #6
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We have the 6CTA, its larger horsepower relative. It's a workhorse for sure.
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Old 08-27-2015, 11:11 AM   #7
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I have had several of the 330 HP version of these engines in boats over the years.

It is a great engine, but has its weak points.

The older ones had an issue with the sea water pumps, so look at those carefully.

The engine is also susceptible to damage caused by over propping, and manufacturers tend to over prop to make claims regarding faster cruising speeds.

For example EVERY Bayliner 4788 that left the factory is over propped with realistic owner load out. Every One.
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Old 08-27-2015, 11:19 AM   #8
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For example EVERY Bayliner 4788 that left the factory is over propped with realistic owner load out. Every One.

Curious what you mean by "realistic owner load out"? Also how did you deal with the over propping in your situation?


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Old 08-27-2015, 11:26 AM   #9
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Curious what you mean by "realistic owner load out"? Also how did you deal with the over propping in your situation?


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OK, from the factory the Bayliner 4788 will make it's WOT RPM target.

Once the owner adds things like a nice skiff, an nice inverter with it's larger supporting house battery bank, and all the other "stuff" the average owner adds to a boat this size the boat will then not make it's RPM target at WOT. This added weight may not seem like much, but the deck crane is rated at 750 lbs and many use a 5-600 lb skiff. The factory house bank is a single 8D battery and most upgrade that adding probably a thousand pounds to the boat.

What I did, AFTER replacing the two Cummins 330 HP engines with factory reman units (the old ngines had high blow by at 900 hours) was to drop the prop pitch from 24" to 22".

This brought my WOT RPM back over my 2800 RPM target and kept my fast cruise EGT at <= 900 degrees, anlong with my fuel consumption right at the factory performance curves for the engine.
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Old 08-27-2015, 11:37 AM   #10
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Very good. Thanks for your explanation. Now I understand.


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Old 08-27-2015, 11:53 AM   #11
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Just to clarify: at 8.5 kts you get 3mpg or 3kpg? Or is it that you cruise at 8.5kts and use 3gph (= 2.8kpg)?
At 9 - 10 mph (1250 rpm), I get 3 miles per gallon (ICW).
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Old 08-27-2015, 11:55 AM   #12
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"For example EVERY Bayliner 4788 that left the factory is over propped with realistic owner load out. Every One."


Kevin - FWIW it is not just Bayliners as we cruise with a bunch of other brands that have similar issues with these Cummins. Sea Ray, Silverton, Tiara are just a few of the many that had these with props that were very aggressive out of the dealers.


Hope this helps
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Old 08-27-2015, 12:51 PM   #13
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"For example EVERY Bayliner 4788 that left the factory is over propped with realistic owner load out. Every One."


Kevin - FWIW it is not just Bayliners as we cruise with a bunch of other brands that have similar issues with these Cummins. Sea Ray, Silverton, Tiara are just a few of the many that had these with props that were very aggressive out of the dealers.


Hope this helps
Thanks Ron!

I always suspected, but never knew that other brands had the same agressive propping issues from the factory.
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Old 08-27-2015, 01:10 PM   #14
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Aftercoolers need to be serviced. The OEM waterpumps(Sherwood) have a tendency to fail early. I think the concensus is that if they are used regularly then you may get decent service out of them. But if the boat has sat around unused for awhile then the pump shafts spin while the seals do not....and that is not good. Anyway, keep a close eye on whether the pump leaks....or evidence of leak(rusted motor mounts). Even if you do not want to join Boat diesel dot com you can peruse the website Tony's Tips - Information about Marine Diesel Engines and Boats from Tony Athens and get TONS of information on these engines.
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Old 08-28-2015, 02:47 AM   #15
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Seaboard Marine website is sbmar.com, has much of the info you need to read.
Specifically look for aftercooler maint and raw water pump upgrade.
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Old 08-28-2015, 08:25 AM   #16
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Those are superb engines when used and propped properly. However at 44,000# that is a heavy boat. Nor problem at all at bow down speeds but if by semi displacement you mean it planes then I wonder if they are big enough.
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Old 08-28-2015, 08:30 AM   #17
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Those are superb engines when used and propped properly. However at 44,000# that is a heavy boat. Nor problem at all at bow down speeds but if by semi displacement you mean it planes then I wonder if they are big enough.
Thanks.

7-9 knot cruise is the boat spec, mid teens max. So it will be hull down for the vast majority of time.

If we decide to proceed there will be a full survey including oil analysis for lugging etc.
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