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Diesels to Avoid?

Old 05-25-2020, 08:08 AM
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Default Diesels to Avoid?

Looking at twin diesel expresses in the 32 to 36 range, Most likely late 90s to 2010, what diesels should I avoid? How many hours until a rebuild is necessary assuming they have been serviced well?

My last diesel boat was powered by D4s, great motors until you needed parts, $$$

Thanks up front.
Old 05-25-2020, 08:26 AM
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Age is more important than hours.
https://www.sbmar.com/featured-artic...diesel-engine/
Personally I think you're going about it the wrong way. Find a good boat first in good condition. Then consider the engine model only after you've noted how well they were maintained. 80% of the boats you find won't be worth a survey. Sad but people don't take care of their boats.

Cummins and Yanmar would be my first pick. But you might
not have much choice with the crappy boats out there for sale.
Old 05-25-2020, 08:29 AM
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Theosea,

CAT, Cummins, and Yanmar are your best bets.

Detroit 92 series suck and Volvo parts are $$.

MAN makes good motors but $$ to keep running.

CAT tells me that knowing when to rebuild is a function of how much fuel the motor has burned, rather than hours- that being said, I was told to expect around 9K hours out of my C12's the way I use them.
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Old 05-25-2020, 08:32 AM
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Originally Posted by theosea View Post
Looking at twin diesel expresses in the 32 to 36 range, Most likely late 90s to 2010, what diesels should I avoid? How many hours until a rebuild is necessary assuming they have been serviced well?

My last diesel boat was powered by D4s, great motors until you needed parts, $$$

Thanks up front.
In that size and power, Cummins are probably the top pick. Any of the 6BTA/QSB or 6CTA/QSC engines are good.

Engine life will be impacted by loading/propping, total fuel burn, quality of filtration (air/oil/water/fuel) and other factors like exhaust riser design (to eliminate water in turbos) as much as good servicing.

Old 05-25-2020, 08:41 AM
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2nd on Yanmars. I had the 500 hp’s in my Luhrs and they were great motors. I had Volvo’s ( 2 sets) in my Phoenix and loved them until it was time for parts, many$$$$. We had about 2000 hours on the first set of TMD 40’s and repowered to get some speed in the boat. WithTAMD 41’s, cruise went from 18 to 26 knots. Those little motors loved to run. The Yanmars had about 2000 hours on them when I sold the Luhrs, and that was about 40% running and 60% trolling. That boat cruised at 27 knots and was 30 knots WOT. The Yanmars never used a drop of oil and the only repairs needed in 5 years was the replacement of the exhaust gaskets once per engine.
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Old 05-25-2020, 08:42 AM
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CAT is my first (and only) pick in that range. I bought my first set of 3116 @ 350 HP in 1992 & ran them to 3500 hours with only minor issues. I sold them in 2003 and the guy is still running them. I bought 3126 @ 420 HP in 2003 and now have 1900 hours of flawless performance. I sure there are other diesels that have performed just as good. But based on my 28 years experience, u cant go wrong with CAT


Old 05-25-2020, 08:49 AM
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Everybody says Volvo parts are expensive

I have 1,400 hours on my D6's and I wouldn't know because I've only bought 1 sensor for my fuel filter
Old 05-25-2020, 08:55 AM
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Originally Posted by tvguy243 View Post
Everybody says Volvo parts are expensive

I have 1,400 hours on my D6's and I wouldn't know because I've only bought 1 sensor for my fuel filter

I agree. My 1st annual oil change on my D4 300's was cheaper than my oil changes on my Yamaha 4 strokes. I was shocked.
Old 05-25-2020, 08:56 AM
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In the 32' to 36' range, you are covering a broad spectrum of HP requirements from 300 hp on the low side to 600 hp on the high side.
In the 300-425 hp range, CAT (3116, 3126 & C7) & Cummins (B330, B370, QSB 380 & QSB 425) are good motors and inexpensive to service and repair, Yanmar is a little more expensive on both maintenance and repair.
In the 425-600 HP range CAT offers the C7 at 461 hp and the C9 at 575 hp and Cummins has the QSC in 450-600 hp ranges.
CAT rates all their motors in gallons consumed before overhaul, and doing the math, for an E-rating (high performance pleasurecraft) if you ran them at full cruise speed 100% of the time, it would be 4,000 hours, and for typical running 75% of the time at cruise speed and 25% at displacement speeds, would net you about 6,000 hours; most people end up running about 50/50 cruise and displacement speeds and that gets you to about 8,000 hours as the TBO. I expect some of the lower hp per size Cummins (i.e. not the 425/440/480 QSB 5.9 or 550 & 600 hp QSC) would garner similar type of hours before overhaul/replacement. But, all those hours assume maintenance is done by the book, and some of those 1,000, 2000 & 3,000 hour service run into the thousands of dollars, even on CAT & Cummins.
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Old 05-25-2020, 09:06 AM
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What ever you buy be sure to get common rail diesels, why throw today's money at yesterday technology. I am on my third set of Volvo diesel, presently have D4's@210, really don't know if parts are expensive never had to buy any, a sensor here and there, engines run like the precision machine they are.
Old 05-25-2020, 11:26 AM
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Really great stuff gents. Much appreciated.
Old 05-25-2020, 11:55 AM
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If you are DIY then the choice is wide. If you need a dealer to service them then chose by what they can handle. There is no point in owning something that can not get serviced. All mid size diesels seem to do a good job. Installed wrong in boat and you’re out $100k.
Old 05-25-2020, 01:12 PM
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Originally Posted by tvguy243 View Post
Everybody says Volvo parts are expensive

I have 1,400 hours on my D6's and I wouldn't know because I've only bought 1 sensor for my fuel filter
You've had great luck with those engines so far, which proves Volvo makes a great engine. I've heard those D series engines have problems with exhaust manifold problems. (I don't recall the hours were when they started having problems..sorry). When you do need a part for those engines, you will find out just how expensive volvo parts really are. People have wondered, for over 30 years, if volvo parts have gold in them...The price Volvo charges for parts go up every year....way faster than the rate of inflation.
Old 05-25-2020, 01:19 PM
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Detroit 92 series suck
They suck a lot of air to run, but unless someone has juiced them up too much and run them on the pins all the time, they are great engines, I know I had a pair of 8v92"s for several years and a few thousand hours, plus know a bunch of people who have them. When I see comments like this I tend to write off anything else the poster has to say as it's obvious they don't have much experience and just trade in urban (or should I say dockside?) legends.
Old 05-25-2020, 02:27 PM
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Agree on the Detroit’s, they will be running long after we are gone. I’ve had a couple boats with them, actually three. Some who have never owned them pass on rumors I think.
Old 05-25-2020, 02:51 PM
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Originally Posted by caltexflanc View Post
They suck a lot of air to run, but unless someone has juiced them up too much and run them on the pins all the time, they are great engines, I know I had a pair of 8v92"s for several years and a few thousand hours, plus know a bunch of people who have them. When I see comments like this I tend to write off anything else the poster has to say as it's obvious they don't have much experience and just trade in urban (or should I say dockside?) legends.
yep, link I posted above explains why DDs are great engines.
Old 05-25-2020, 02:56 PM
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Shake N Bake did have a lot of issues with a pair that I read in other threads so that is real life experience. I believe they were run a lot in a charter boat and even rebuilt once. Usually that equates to long engine life but it seems on the 92 series (I have a pair in my 46) is overall a good engine for pleasure craft. I only run mine at around 1800 RPM. Zero issues in the almost 2 years I have run them. Not saying they are not good commercially but most pleasure boat guys seem happy with them. Do agree with shark and Caltex that there is more to the story. But shake n bake is not reporting rumors either.
Old 05-25-2020, 02:59 PM
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Guess I got to add my 2 two cents, because no one mentioned John Deere. I have a 6068SFM50 RATED AT 265 horse power. Love it, its a work horse and 4100 hours and nothing major. My advice would be no matter what you go with, make sure you can get parts and service in you home port, Can you get something if you cruise up or down the coast and break down away from home? It would suck to be stuck in another port for days waiting on parts. Tightlines and good luck,
Old 05-25-2020, 03:10 PM
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Originally Posted by CaptnJuff View Post
Age is more important than hours.
https://www.sbmar.com/featured-artic...diesel-engine/
Personally I think you're going about it the wrong way. Find a good boat first in good condition. Then consider the engine model only after you've noted how well they were maintained. 80% of the boats you find won't be worth a survey. Sad but people don't take care of their boats.

Cummins and Yanmar would be my first pick. But you might
not have much choice with the crappy boats out there for sale.
This is the most important factor posted so far. Then brand, parts/tech availability. Price on parts also is a big factor but not if they don't need them that often. But they will need them for sure to some degree. Best way to ward off the parts boogyman is maintenance up front.

Use it or lose it also comes into play. They need to be run on a regular basis.
Old 05-25-2020, 04:19 PM
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Cummins, Deere, Yanmar, Cat, Volvo, in that order. Volvo SUCK's, will never own another one.

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