38 - 40ft SeaRay which diesel engine is best?

Ok guys,

I'm sick and BROKE over these 8.1's now that I bought TWO replacements in 5 weeks!!! Which diesel engines are most reliable and efficient because I'm starting my research for the next boat.

I'm back and forth between a 2005 and newer Sundancer 380-400 and a 2005 and newer Sedan 40-42. I just have no hands on with diesels so that's why I ask the question to others that might have a little more experience on running them

Thanks in advance guys

Hi John,

I'm so sorry to hear about your 8.1 issues. Those owners here will be interested in your details.

I don't know what years/styles you are considering and this may turn into a "is a Honda generator on the swim platform OK" kind of thread, but here goes. Without trying to turn it into a Ford vs. Chevy truck argument - it seems like your choice would be CATs or Cummins, with an outside chance of Volvos - I've seen one or two of those in 460's. Now that I've said that, not many 38's had diesels. More 400/410 DAs did however. Are you looking to go any larger? If its 400/410 DAs in the '97 - '03 range, you'll be looking at CAT 3116/3126's. The 40-44 DBs had these engines or the Cummins 6B or 6CTA (I think - I'm not a Cummins expert, so I'll let them chime in here).

I'm a believer in maint records and annual oil samples to review prior to purchase. CATs (3116/3126) had problems early on with soft blocks and valve issues - those have all been fixed by CAT long ago. I've owned 3126s and love how economically and reliably they run. Service and parts for me were right across the street at the local CAT dealer; consumable parts were cheap - filters, belts, hoses, oil sample kits, etc. There are a lot of articles here on them.

I think you might want to list the specific years/styles of Sea Rays that you are looking for and you might get more detailed answers.

Maybe boating is not for you.......Seriously, Diesels can have problems too.......bigger boat, bigger problems......Properly maintained, gas and diesel engines should both be reliable - yes, maintenance on the diesels will be more, but the payoff is longer engine life......I wouldn't get a bigger boat just to have diesel engines....

I wouldn't either, but I haven't experienced failures like that either. That's extreme and I think would send any reasonable person in another direction.

carterchapman said:

Hi John,

I'm so sorry to hear about your 8.1 issues. Those owners here will be interested in your details.

I don't know what years/styles you are considering and this may turn into a "is a Honda generator on the swim platform OK" kind of thread, but here goes. Without trying to turn it into a Ford vs. Chevy truck argument - it seems like your choice would be CATs or Cummins, with an outside chance of Volvos - I've seen one or two of those in 460's. Now that I've said that, not many 38's had diesels. More 400/410 DAs did however. Are you looking to go any larger? If its 400/410 DAs in the '97 - '03 range, you'll be looking at CAT 3116/3126's. The 40-44 DBs had these engines or the Cummins 6B or 6CTA (I think - I'm not a Cummins expert, so I'll let them chime in here).

I'm a believer in maint records and annual oil samples to review prior to purchase. CATs (3116/3126) had problems early on with soft blocks and valve issues - those have all been fixed by CAT long ago. I've owned 3126s and love how economically and reliably they run. Service and parts for me were right across the street at the local CAT dealer; consumable parts were cheap - filters, belts, hoses, oil sample kits, etc. There are a lot of articles here on them.

I think you might want to list the specific years/styles of Sea Rays that you are looking for and you might get more detailed answers.

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I'm back and forth between a 2005 Sundancer 380-400 and a 2005 Sedan 40-42. I just have no hands on with diesels so that's why I ask the question to others that might have a little more experience on running them.

I've run big blocks in Trucks and Cars for many years so I'm also good there, but take you car / truck engine and put the pedal to the floor every time you leave a red light and leave it 3/4 of the way there for a couple of hours on a trip and see how long the engine holds up. Diesels however will run all day long in that environment and more economically.

Ididntdoit said:

Maybe boating is not for you.......Seriously, Diesels can have problems too.......bigger boat, bigger problems......Properly maintained, gas and diesel engines should both be reliable - yes, maintenance on the diesels will be more, but the payoff is longer engine life......I wouldn't get a bigger boat just to have diesel engines....

Click to expand...

I've been boating since I was 4, owned 7-10 boats in my personal life and did a full stint in the Navy so I'm pretty good with boating in general LOL.

I have no issues with proper & regular maintenance I can send you a spread sheet that would boggle your mind. Its been an open wallet for upgrades and top notch parts no skimping here EVER.

The only reason why I'd go a little bigger is for more room to extend our liveaboard time, right now we get a little cramped after a week.

Might be a conversation for a different thread, but what happened to the 8.1's?

Sorry to hear about your troubles John. When the family and I are out cruising they nap, relax and enjoy the ride. Seeing how you maintain your vessel and still have issues I sit there and worry about every sound that i think is out of the norm when it comes to my engines. Will be keeping a close eye on this thread as we are on the quest for diesels as well. Mostly for the reduced co emissions as well as longevity and economy.

The first one the heat exchanger went and took the head gasket out. The heat exchanger was inspected the beginning of last season and looked fine, come to find out the inside was questionable. And we blew a head gasket, so we did a full head job and re-surfaced and rebuilt them. Ran that for 29 hours and it then grenaded this season. So we did a long block on it got it all set and back and while we were out running it through its paces the Starboard's main seal goes and we lost oil pressure and shut it down but it was too late.

Irie308 said:

Sorry to hear about your troubles John. When the family and I are out cruising they nap, relax and enjoy the ride. Seeing how you maintain your vessel and still have issues I sit there and worry about every sound that i think is out of the norm when it comes to my engines. Will be keeping a close eye on this thread as we are on the quest for diesels as well. Mostly for the reduced co emissions as well as longevity and economy.

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Thanks Buddy, yeah this is a tough one to swallow. If I cut corners I would expect it but that's not the case. Every sound I hear I get a knee jerk reaction. It goes in Monday am for the next one, hopefully it will be only a week. I'm so deep in this one it might be awhile before I sell it but then again the next owner wont have anything to fix or upgrade for years LOL!

It's not just the longevity and fuel economy of the diesel engines, its the raw "grunt" they have which is especially useful when manouvering at slow speeds. Read docking.

My fellow dockmates will jokingly walk away as I back the boat into my slip, looking at each other and saying "Oh he doesn't need any help, he has diesels".

Ctsearay said:

The first one the heat exchanger went and took the head gasket out. The heat exchanger was inspected the beginning of last season and looked fine, come to find out the inside was questionable. And we blew a head gasket, so we did a full head job and re-surfaced and rebuilt them. Ran that for 29 hours and it then grenaded this season. So we did a long block on it got it all set and back and while we were out running it through its paces the Starboard's main seal goes and we lost oil pressure and shut it down but it was too late.

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Jesus. Sorry to hear that. And here I was all excited because a 340 with the 8.1's finally came to market (most of them have been 7.4 horizons with reversion issues and log exhausts)

I think I need to buy a rowboat and call it a day

Ours sat in raw salt water for its first 6 years as a floating condo, then the rest of it life it sat on blocks on dry land so I envisioned issues which the first 4 years we owned it we worked out a lot of little bugs and brought her up to better than new. This season however was a big one for costs.

If you get snake bit, definitely cheaper to address with gas. As with anything, there are always horror stories that surface.

CAT
I've heard of the block issues with CAT 3126 as mentioned by FrankW in previous posts and Carter in this one. But I personally had a great experience with the 3116's in my 410DA. Super reliable and economical. Loved 'em.

Cummins
Most people seem to have a good experience here. Although, there is guy in my marina that has a 2005 420DB that luckily bought the extended warranty when he purchased used from MM. He had three replacements in a relatively short time and they are Cummins. One failed during the sea trial by Cummins. What's up with that?

Volvo's
Dockmate has Volvo pods in a 40' Monterey. He has to pull the boat for drive service every year. On a southern lake, that's crazy. We typically pull after about 5 years, unless a problem dictates otherwise.

MANs
Nevermind, not gonna go there but so far, fingers crossed... Happy, Happy, Happy.

Since I was incompletely quoted, here is an addendum to post #14 above:

Caterpillar did have a metallurgy problem with some blocks from a French foundry....on 3126 engines only; the 3116 was not involved. This is a problem that caused early cylinder wear and was evidenced by high oil consumption and blow by in the crankcase. Cat identified the problem and replaced all the affected engines up to about 2004. By then the soft block engines were worked out of the system because they were either replaced or worn out. Any 3126 you see now is well past the time when a soft block would occur if it were going to, so this risk really doesn't enter into the buying equation today. If you are concerned, just ask Caterpillar to do a "Blow-By test" as a part of their engine survey. This is a proprietary test Cat can do which measures the crankcase pressue to see if excessive combustion gasses are getting past the piston.


My own opinion is:

I've owned 3116's for 20+ years. They are extremely reliable, never smoke and are very economical. I am spending far less maintaining 3116's than what I spent maintaining a pair of gas big blocks....and a fraction of the fuel cost as well. It would be real hard to beat Caterpillars.

I have Cummins owners all around me in the marina and while Cummins generally makes good engines, their designs require more maintenance expense, mostly because of the need to frequently clean the heat exchangers and aftercoolers. Some Cummins C series engines have had problems dropping valves, but I don't know years or models.

Volvos make good equipment, but parts and service are sparse in some areas so check in your area before signing on for the trip.

Ctsearay....my condolences from a fellow 360 owner. I thought I was having a rough year..2 batteries, battery charger, impellers, coolant leaks (age related) and an electric fuel pump problem.
Hope you are over the hump, mtc wise, and will still enjoy the boat.

I struggled with the same thing while boat shopping last year. While not a mechanic by trade, I've been fooling around with, and fixing my own, gas motors for almost 50 years. Very comfortable maintaining, diagnosing mechanical issues, and repairing gassers. Especially Mercruiser which are actually small block and big block Chevys that just about every Motörhead in the free world has experience with.
If you ever have to replace a motor, small blocks are reasonably priced, but big blocks are not. They aren't as expensive as diesels to replace, but they are pretty high up there. Factor in the added fuel costs for running 8.1's, and the diesels start looking a lot better.
I've never owned a diesel in anything before, and never put a finger on one.
I bought this boat with Cat 3126's and absolutely love it. I'm still nervous about them because diesel is a different animal, but they run incredibly well and really suit the boat nicely.
My fuel economy in this boat is about the same as it was on my 300 Sundancer with 5.7's. That alone makes diesels a no brainer for me.
One maintenance complaint I have so far with my Cats is the Zincs in the aftercooler. They are real PIA to get out of otherwise very accessible holes. I think it's a lousy design. But, I believe that Frank W's advice to change them more frequently so they don't get stuck in there is solid and I intend to follow it.
So far my verdict on the Cats is very positive. Other than a tight bilge (not the motors fault), they're a perfect match for my 410.
My friend has an 05 420 DA with Cummins in it. He just had a problem with a dropped valve seat within the last two weeks. Apparently it's a design issue that Cummins is aware of. He had the head and one piston replaced, and a new sleeve in the effected cylinder and it runs like new.
Boat is a bit faster than mine for sure, and has an unbelievable amount of room to work in the bilge. Sea Ray got that design right for owner maintenance.
That huge bilge and hardtop make me wish I could have swung one. Other than that, my 410 is a much better value for essentially the same boat.
He's going to try to recoup some of the cost for the new head from Cummins. I think they are on version #3 of the head design for those motors. Certified Cummins mechanic that did the job said they finally got it right. He wouldn't be afraid to go with those motors as long as the heads have been done on them. If not, he said he would knock 15k from the purchase price and have the heads replaced on both motors as soon as he took title to a boat to avoid possible future problems.
As far as the aftercooler and heat exchanger maintenance on the Cummins: I spent the afternoon with my friend when he did it himself. IMHO: Very easy job for a DIY'er of moderate skill level. Very easy to remove and reinstall them on the motors too. Much easier than the aftercoolers on my Cats look.
So my verdict on the Cummins is also very positive contingent on the (pre-2007?) heads having been replaced, or if the cost of that job were factored in to the purchase price of a boat.

Sorry for your pains!

You may find you have a hard time finding 38-40's in New England with diesels and if you do you will pay a huge premium. When we bought our boat there was exactly 1 Sundancer 40 with diesels for sale north of MD, it was priced less than 20k cheaper than the same year 420's from MD to MA and not in as good of condition as most of them.

That said any diesel could suffer the same pains but cost significantly more. There are plenty of horror stories including the dropped valve story mentioned previously.

Guys thanks SO much I really appreciate it. The upgrades and things I've done to this boat is exhausting just to look at the list. It truly has been an open wallet for its life. The past 3 years after purchasing her I have put in 6-8k a year just maintenance, upgrading and replacing stuff. Heck I even upgraded the speaker wires to quality stuff throughout the entire boat, inverter, 6 AGM batteries at $325 each, charging system just because I wanted to be good when on the hook. This year with the long blocks I'm easily on track for 42k and the only thing left is the fridges and freezer and that's not happening this year although they don't really need it but in my head they could be colder.

So the new long blocks have a 3 year warranty on them. I'm thinking about possibly mid year next season putting her up for sale but not pushing her hard to sell it. I don't know maybe if the right broker comes along and do a trade for the right diesel it will go. I'll tell you what I can almost guarantee the next owner won't have to do anything, my luck for a VERY long time

fwebster said:

Since I was incompletely quoted, here is an addendum to post #14 above:

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Dang Frank, it was only a reference, not a quote. With over 10,000 posts, not sure there is enough memory on the server to quote you completely. I only referenced the 3126 for soft block issues so at least it was accurate. Anyway, thanks for your technical comments and filling in the blanks, very much appreciated.