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Volvo D6 vs Cummins QSB 380 (No Dealer Service for 1000 miles

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Volvo D6 vs Cummins QSB 380 (No Dealer Service for 1000 miles

Old 10-13-2019, 06:30 PM
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Default Volvo D6 vs Cummins QSB 380 (No Dealer Service for 1000 miles

I read many pages of posts about these two motors, but with no marine diesel dealer on the island (We do have a Yanmar dealer, however my understanding is that they do not have a single full service level person on staff for over 18 months.) I want to make the best choice.

Buying a boat to bring to the USVI to charter. I have narrowed it down to two boats same age with twin Diesels with shafts (no drives that require more $ and expertise to maintain/repair)
The choice is a pairs of Volvo D6 vs Cummins QSB 380. Both boats only have about 500-600 hours on the motors. I am planning to put several thousand hours on these engines and do the basic services myself, if I need to. I would prefer not to do it all the time, but I am capable as long as the key parts are accessible.

The boat with Cummins has two years left on the factory warranty. This sounds great, except there appears to not be a dealer in the USVI. The closest one is in Puerto Rico, after that it's Miami or dealing with a non-US dealer.

The alternative: The only other boat I found acceptable has a pair of Yamaha F350's. We have a full service Yamaha dealer, but without mentioning the brand/model of boat, it can only fit Yamaha 350s. The current motors on this boat are 2012 models. I have basically not gone in this direction because outboards are no match for diesels in longevity and I am not in needing high HP to get anywhere in a rush.

I am open to all thoughtful suggestions.

Thank you!
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Old 10-13-2019, 06:44 PM
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read the maintenance schedules, see if you are capable of all the maintenance

look up the engine models for known issues/failures, see if there are any, and if there are if its something that can be handled where the boat will be

warranty is worthless unless there is a dealer you can bring the boat to for service.

can you get parts? whats the cost? that is probably the real question.

ps. i have a feeling whats left of that warranty wont apply if you are using in a commercial application
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Old 10-13-2019, 07:58 PM
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Cummins all the way. Compare the prices of parts for either one. I have had experience with both brands and found Volvo to be way more expensive to maintain. Compare service points. The QSB has the raw water pump up high and easy to get at.
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Old 10-13-2019, 08:16 PM
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Maintained properly a QSB will not require any parts other then service for 1000’s of hours. My sister boat needed a pump at 800 hours, no other hard parts. My boat with 440 hrs , nothing yet.
Make sure installed correct or that changes everything. And don’t fall for that 80% load running. Back off and get 8,000 hours easy.
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Old 10-13-2019, 08:25 PM
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Cummins for price of parts and availability.
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Old 10-13-2019, 08:28 PM
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Volvo too expensive for parts .
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Old 10-13-2019, 08:54 PM
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Cummins are the pick for diesels in this size range, no question.

Basic maintenance and servicing can be done by yourself easily - oil changes, air filters, fuel filters, zinc anodes.

More advanced items can be done without too much problem - aftercoolers and heat exchangers can be removed and serviced by yourself, with a good basic tool kit.

If you get the Cummins, I have two suggestions. 1 - Buy two complete new seawater pumps from Seaboard Marine (SMX models), replace the stock units and keep them as spares. 2. Buy and install the multistage fuel filter kit that Seaboard Marine also sells.
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Old 10-13-2019, 10:58 PM
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I’d pick the Cummins over Volvo, even without looking at them!
Even better would be mechanical Cummins 370s, you can work on them without tech training or electronic diagnostic tools.
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Old 10-14-2019, 02:23 AM
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Hello, based upon experience with both engines in various applications, I would go with Cummins all the way. The Volvo D6 is a decent engine, however, going on the ones we have in service here (and there's a lot of them), the simply do not have the longevity of the Cummins, so much of the Volvo is electronically controlled and requires the Volvo Vodia diagnostic software and fairly regular updates, a tool that Volvo charges dealers a lot to have so the costs have to get passed on, also much of the controls of the EVC system are electronic and very sensitive to battery power. The Cummins although later models are also electronic but for some reason are far more robust, parts are cheaper, the tie up with Mercruiser worked well also, Cummins Mercruiser Diesel, the Vesselview is a really handy tool. If electronic throttles and gears, Glendinning are very good. There is no doubt the Cummins are more vocal that Volvo, much more of a diesel noise but IMHO a small pay off, as another poster said the water pumps are easy to get at, although we have had a few that start to leak earlier than we would have expected, if memory serves they are made by Sherwood and are easily available, also if I remember rightly when the Coastguard or navy were testing replacement motors Cummins came out top. One thing to look out for in a particular install is that all services are handed, that is dipsticks, filters etc are mounted inboard to make life easier, also make sure the engine mounted gauges work well. Hope this helps.
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Old 10-14-2019, 06:46 AM
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Originally Posted by kapnD View Post
I’d pick the Cummins over Volvo, even without looking at them!
Even better would be mechanical Cummins 370s, you can work on them without tech training or electronic diagnostic tools.

^^^^^^ This

Mechanical injection Cummins 6B or 6C series all day long, very simple and robust.
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Old 10-14-2019, 12:28 PM
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80% Load?
Are you saying that I should not run at 80% or exceed 80% of WOT?
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Old 10-14-2019, 12:31 PM
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Thank you very much!
I think the boat with the Cummins engines is the boat for me. I am going to find more information about doing the services myself, including servicing the aftercoolers and heat exchangers. It sounds like if I can get to them, it should not be too difficult.
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Old 10-14-2019, 12:39 PM
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I’m suggesting constant 80% load running will not yield hours like I mentioned. Back off , watch your fuel consumption and compare it to Cummins data sheet and you will be fine.
a customer of mine just bought a hi end boat with a QSC single 600hp. He ran it for 120 hours exactly how the dealer recommend. The boat is 23,000 lb, running 26kn . That’s a lot of pushing for a single . I check out his engine and the paint is changing color already. Not a good sign yet the computer shows <80 load.
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Old 10-14-2019, 12:43 PM
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Second the Cummins plugs. I'm in the marine diesel business and the Cummins QSB 380 has been a solid machine. Can things go wrong? Yep, but it is rare. Been around some D4 and D6 that have blown for no apparent reason. Buy parts for a Volvo and you will cry. Cummins parts expensive too, but not nearly as bad.

Edit: and yes, no need to run 80% on a high output diesel. Find the boat's "sweet spot" and if it is 65-70%, better yet. These engines could run 20% power and live forever. Old wive's tale, that 80% thing. Maybe on old huge NA beasts, not the new modern stuff.
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Old 10-14-2019, 12:49 PM
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Thank you very much for this advice!
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Old 10-14-2019, 12:50 PM
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Understood!
Thanks
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Old 10-14-2019, 12:52 PM
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The Volvo's are great engines. Very impressive. Very high-tech. I've owned some (D4 and D6). However, when it comes time for service and or repair, they are a train wreck. Very expensive parts. The Cummins, which I have also had experience with, are hands-down the better choice.
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Old 10-14-2019, 01:05 PM
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These hi load #’s came in when boat manufacturers wanted high speed from small displacement diesel. No one wants a 20kn cruise when they can get 28kn. So the dealer goes to the engine builder and has them test engine life figured on 100-300 hours of use per year. They just need to get past a reasonable time frame. Let’s say 10 years. Now you are past the warranty and onto the second or third owner. Just check YW and see how many 1500 hours cruises have not had any major engine work or even new engines. Cat,Cummins, Volvo it doesn’t matter. Small displacement just can’t handle that type of loading long term. So how does a Lobsterman get 30,000 hours out of a Deere, cat, Volvo, cummins? It all about load , fuel consumption and maintenance.
No matter how you figure it a diesel can burn just so much fuel before it wears out. This is enhanced by excessive heat from high percent loading.
Back off load by 20% and get 200% more life
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Old 10-14-2019, 04:20 PM
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Going a bit from memory here cause I don’t have the specs in front of me, so the details may not be quite right.

Those 5.9 Cummins were made in a wide range of outputs from around 220hp up to 480hp. I think the 380hp version is the lowest of recreational ratings. Different ratings achieved by tweaking exhaust, turbos, fuel systems, and higher max rpm.

Cummins rec rating is no more than 400hrs per year and no more than 1 hour in 8 above 80% load. Load is a calculated value but great thing about QSB’s with VesselView displays is you can easily see the engine load in the engine display pages.

What the other guys are saying is that if you regulate load and max RPM well below the limits you are effectively turning the engine into a commercial spec and you should get very long life.

One very important aspect in achieving that which hasn’t been touched on yet is propping. Be very conservative in prop selection which will help immensely in managing engine load.
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Old 10-14-2019, 04:47 PM
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Originally Posted by Conchyjodyoos View Post



^^^^^^ This

Mechanical injection Cummins 6B or 6C series all day long, very simple and robust.
The C-Rail is so much more fuel efficient and quieter.
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