Mainship Preferred Diesel- Catapillar or Yanmar?

Riverguy said:

Never heard this before, so I checked...and it's apparently an urban myth (what we used to call an 'old wives' tale).

1) The 5.1 litre Yanmar 370hp 6LYA in our MS390 weighs 1,168 lbs. The 5.9 litre Cummins 370hp 6BTA "Diamond" engines in our 4788 weigh 1,140lbs.


So, since the Yanmar is actually a smaller displacement engine than the Cummins, and the Yanmar is actually --heavier-- therefore one should presume beefier construction on a "lbs-per-displacement" basis. These engines are virtually identical (with a slight edge to Yanmar) on a 'lbs-per-horsepower' basis. In any case, I don't think either of these is valid basis to trash an engine for 'theoretical longevity', but in any case, the notion of a "much lighter weight" Yanmar" is totally false.

2) The 5.1 litre 6LYA is rated for 370hp at 3,3000, the 5.9 litre Cummins is rated for 370hp at 3,000 rpm. Two takeaways here -- first, the rpm difference is nearly meaningless. Second, as we've learned over the last 40 years, smaller displacement engines running at faster RPMs to achieve similar horsepower result in --greater-- reliability, because they develop less torque for any given horsepower. This reduces the load on bearings, piston rings and everything else in the engine. Combine this with the incredible advances in engine oils, metal alloys and precision machining and it's easy to see why new, faster-spinning engines are more reliable, not less.

Sorry...I don't mean to contradict so flatly, but if we are going to trash a particular brand of engine, I expect we all want to get our facts straight first.

I own both the Yanmar and the Cummins. Both great engines. Slightly less troubles with the Yanmar...

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I don't think I was trashing Yanmar. My comment was based on the fact that what was referred to by the salesman as the preferred engine was a CAT 3216, and the title of the thread was a comparison between that CAT and a Yanmar. The 3126 marine engine weighs just over 1800# and produces 250 HP at 2400 rpm. https://www.google.com/search?q=cat+3126+specs&oq=cat+3126+specs&aqs=chrome..69i57j69i60j69i61j0l3.25269j0j4&client=ms-android-google&sourceid=chrome-mobile&ie=UTF-8#imgrc=sWP5ZS3EN0RThM:

The Yanmar 6Lya marine engine weighs a lot less, turns faster and produces more HP, so my expectation is that it would not last as long as the CAT, all other factors being equal. Perhaps that is what the salesman meant.

"The 5.1 litre Yanmar 370hp 6LYA in our MS390 weighs 1,168 lbs. The 5.9 litre Cummins 370hp 6BTA "Diamond" engines in our 4788 weigh 1,140lbs."

I have a hard time believing these numbers. As you said the Yanmar is dry and maybe the Cummins weight is with full fluids. Also some manufacturers leave out stuff like exhaust mixers. The Cummins sure looks bigger and heavier.

"Second, as we've learned over the last 40 years, smaller displacement engines running at faster RPMs to achieve similar horsepower result in --greater-- reliability, because they develop less torque for any given horsepower. "

It is often sometimes valuable to test a hypothesis at its extremes. Do you really believe that the 4,000 rpm Styer and Yanmar 4BY engines can last longer putting out 90 hp per liter than a Gardner putting out 127 hp or 12 hp per liter at 1,500 rpm?

You are correct that high rpm engines produce less torque to make the same hp as a slow NA engine. But the NA compensates with more beef, much more beef. Also high rpm does wear engines. Better metallurgy, cooling and oil helps, but....

David

djmarchand said:

"The 5.1 litre Yanmar 370hp 6LYA in our MS390 weighs 1,168 lbs. The 5.9 litre Cummins 370hp 6BTA "Diamond" engines in our 4788 weigh 1,140lbs."

I have a hard time believing these numbers. As you said the Yanmar is dry and maybe the Cummins weight is with full fluids. Also some manufacturers leave out stuff like exhaust mixers. The Cummins sure looks bigger and heavier.

"Second, as we've learned over the last 40 years, smaller displacement engines running at faster RPMs to achieve similar horsepower result in --greater-- reliability, because they develop less torque for any given horsepower. "

It is often sometimes valuable to test a hypothesis at its extremes. Do you really believe that the 4,000 rpm Styer and Yanmar 4BY engines can last longer putting out 90 hp per liter than a Gardner putting out 127 hp or 12 hp per liter at 1,500 rpm?

You are correct that high rpm engines produce less torque to make the same hp as a slow NA engine. But the NA compensates with more beef, much more beef. Also high rpm does wear engines. Better metallurgy, cooling and oil helps, but....

David

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Having owned a 370 hp Yanmar 6LYA in a 28' Albin and a 270 hp CAT 3306 in my current boat, and worked on both, it just doesn't seem plausible that the Yanmar will outlast the CAT, all things being equal in terms of maintenance and usage. The Yanmar is, IMHO, a 5,000 hour engine and the CAT is a 50,000 hour engine. Perhaps that is why, even though Yanmar makes industrial engines you won't see many large pieces of equipment sporting Yanmars.

Not having owned or worked on a Cummins, I have no opinion on that.

djmarchand said:

"The 5.1 litre Yanmar 370hp 6LYA in our MS390 weighs 1,168 lbs. The 5.9 litre Cummins 370hp 6BTA "Diamond" engines in our 4788 weigh 1,140lbs."

I have a hard time believing these numbers....

David

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Ok...happy to help you with that.

Fifty-thousand hour Cat3306?

Delfin said:

...IMHO, a 5,000 hour engine and the CAT is a 50,000 hour engine.

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Wow. That's incredible! I'm interested in what you saw after owning both that led you to believe that the Cat 3306 would last 45,000 hours longer?


One thing to bear in mind is that the Cat 3306 is a very different engine from a 3116/3126.


By the way, there is a "confidential" recall on Cat 3306 engines with bad connecting rods. Thousands of engines, as I understand. Might want to see if yours is affected.

Low Engine Hours = Buyer Beware?

jefndeb said:

Thanks much...so as far as hours go,..... what would be considered low. medium or high...or is that another question that is really objectionable....
Thanks

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No...it's a very good question.


Having been burned when I thought I was getting a steal on a 'low hours' boat, I've come to the conclusion that (in boats) "low hours" should be a warning flag, rather than a selling point.

First, you should read Tony Athen's article on "Marine Age" of engines. Several of us here have referenced it.

So, taking Tony's analysis a short step further...why would "low hours" be a cause for concern?

Most marine diesels fail because of neglect...and engines that are underused are very frequently neglected. After reading up on "Marine Age", remember that 'rust never sleeps', and that includes all forms of marine corrosion, electrolytic, galvanic, impressed current and crevice corrosion all take their toll and in many cases, it is >>underused<< engines that get the worst of it.

Here's an example.


A 20 year old boat is advertised as a "one owner" boat and it only has 480 hours on the engine(s). That means that this engine has been used an average of 24 hours per year or two hours per month. Two hours is barely enough time to get the engine and transmission thoroughly warmed up. Moreover, it is highly unlikely that this engine was run regularly once a month -- far more likely that this engine has had extended periods of disuse. Hmmm...so was anyone checking the anodes every month? Very unlikely. Was engine oil that "only had 24 hours on it" getting changed once a year anyway? Also unlikely. What are the chances that the owner understood the concept of "Marine Age", and maintained the engine accordingly? You get my drift...

A couple of observations:

Lower-priced, mass market boats (including Mainship) have always been especially attractive to first-time, less knowledgable owners in both the new and used markets. Moreover, an under-used boat (of any brand) may have been a wealthy person's status-toy. These boats are also very frequently underused. Over forty years of boat ownership, I have known dozens of boat owners that fit into either of these classes. The common theme is that they are 'boat owners' but not really 'boaters'. Boaters who own boats USE them, and boaters who use their boats tend to MAINTAIN them.

To me, this means that it is quite likely that an under-used boat was also under-maintained.

Any time I see a boat with less than 50 engine hours per year, I have to ask why, and I am very skeptical as to whether this boat was 'used enough' to ensure that it was getting regular attention and maintenence. Unless there is a known reason for extended periods of underuse (like sitting on the hard seven months per year in New England), a 'low hours' Mainship would scare me, no matter what engine it has.

If you are looking at 20 year old boats, you should be seeing somewhere between 1,500-2,000 hours minimum. Anything less should raise suspicions.

I am not saying that there are no underused marine engines that were properly maintained anyway. I am saying that the liklihood is "underused is under-maintained".

If you are seeing substantially more than 100 hours per year, this should not necessarily concern you. The "design goal" (intended use-case) for 'MP' (marine pleasure) use diesels is typically 250 hours-per-year across all manufacturers. When properly maintained (and setting aside any 'known' problem engines), any of the diesels you see in these boats should easily last 7,000 hours or more before rebuilding, if you are remaining within the performance envelope the engine was built for. In many cases (and depending on how hard you run it and how well you maintain it) you could see 10,000 or 20,000 hours.

https://www.sbmar.com/featured-article/marine-age-the-real-age-of-a-marine-diesel-engine/

Riverguy said:

I presently own both the Yanmar 6LYA-STP and the Cummins 6BTA "Diamond". The Yanmar is 5.1 litres and weighs 1,169lbs. The Cummins is 5.9 litres and weighs 1,140 lbs. These are from the factory spec sheets. Yanmar specifies the weight as "dry", the Cummins sheet doesn't say wet or dry. Either way, the Yanmar is HEAVIER.



I would love to know where this myth about the Yanmar engines being 'light' came from???.


Tony Athens (whom I have hired in the past and worked with personally) is truly a wonderful resource, but he is a Cummins factory guy (even though he no longer works for Cummins). Certainly he is knowledgable across all brands, but I don't think his opinions on Yanmar serviceability are the definitive last word.

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"The Yanmar is 5.1 litres and weighs 1,169lbs. The Cummins is 5.9 litres and weighs 1,140 lbs. These are from the factory spec sheets. Yanmar specifies the weight as "dry", the Cummins sheet doesn't say wet or dry."

FWIW - the Cummins weight is for a dry engine.

When I bought Sonas in early 2016 she had just under 5000 hours on her engines. So for a 14 year old boat, that averages 357 hours per year. She had been cruised through the Caribbean, loop, north east, Gulf. Basically all over. Based on her logs and the half ton of marked charts on her. She also had maintenance logs and an extensive spare parts inventory. The boat was laid up every year at American Custom Yachts in Stuart and maintained there. I had Shearwater do the engines surveys.

I had no qualms buying her.

A lot of that was the above, but also I had been crawling around target boats for a couple of years, including Selene and SeaHorse. Some of the conditions of the vessels themselves and the ERs were deplorable.

There are a lot of things that indicate a well maintained engine, add to that quality engine surveys and you can make yourself comfortable.

Riverguy said:

Wow. That's incredible! I'm interested in what you saw after owning both that led you to believe that the Cat 3306 would last 45,000 hours longer?

.

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Talking to a CAT engineer who helped in the initial design of the motor, and whose experience with it on the North Slope exposed him to genset applications that got that many hours without much difficulty. Those number of hours translates to around 2.5 million miles on a truck engine, which is strong mileage, but not that unusual. By the way, since Yanmar makes industrial engines, any thoughts on why you never seem to see one in an 18 wheeler, bulldozer, etc? Maybe there are some, but they seem kind of rare.

Delfin said:

Talking to a CAT engineer who helped in the initial design of the motor, and whose experience with it on the North Slope exposed him to genset applications that got that many hours without much difficulty. Those number of hours translates to around 2.5 million miles on a truck engine, which is strong mileage, but not that unusual. By the way, since Yanmar makes industrial engines, any thoughts on why you never seem to see one in an 18 wheeler, bulldozer, etc? Maybe there are some, but they seem kind of rare.

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"By the way, since Yanmar makes industrial engines, any thoughts on why you never seem to see one in an 18 wheeler, bulldozer, etc?"

Same thing with the Cummins 6B - only in light duty pickups. Any of the bus and heavier applications you see the 6c series.

smitty477 said:

"The Yanmar is 5.1 litres and weighs 1,169lbs. The Cummins is 5.9 litres and weighs 1,140 lbs. These are from the factory spec sheets. Yanmar specifies the weight as "dry", the Cummins sheet doesn't say wet or dry."

FWIW - the Cummins weight is for a dry engine.

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Thanks, I had guessed as much. So then Yanmar is indeed heavier. Quite a bit heavier in terms of lbs-per-litre of displacement. The 6LYA is 229lbs-per-liter and the 6BTA is 193lbs-per-liter -- that's about 20% heavier.

Riverguy said:

Thanks, I had guessed as much. So then Yanmar is indeed heavier. Quite a bit heavier in terms of lbs-per-litre of displacement. The 6LYA is 229lbs-per-liter and the 6BTA is 193lbs-per-liter -- that's about 20% heavier.

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lbs/liter of displacement is hardly a measure of "heavy", if heavy somehow translate to longevity. The reason is that in order to get the hp out of a lighter engine, Yanmar, as do many manufacturers, made it turn faster. All other factors being equal, higher displacement to achieve required hp while turning at a slower max rpm with the same weight of metal will run longer than a smaller displacement motor turning faster of the same weight. The OP asked about a CAT 3126 and whether the salesman was correct that it was the "preferred" engine for the Mainship. Whether his use of the term is just sales speak, or whether he was referring to the empirical fact that the CAT 3216 has higher displacement than the Yanmar, turns slower than the Yanmar to produce its rated hp and weighs a lot more might have been what he was thinking.

Perhaps the reluctance with Yanmars is it's not American Iron same applies to Hinos both are surprisingly good motors...

You might want to check the exhaust raw water injection point. Based on solid advice from others here, it was a real issue on turbo Yanmar 4cyls, potentially leading to standing water affecting risers/angles and turbos. ? affects 6cyl versions.

This has already been said, buy I didn't want it to get lost in the other discussions. For Mainship the recommended engine is the Yanmar or cummins. Cat did in fact have issues with the 3116/3126 blocks built in France and they did have a recall on them. Whether the boat you look at has had it replaced or not should be a concern. For the seller to say the 3126 is recommended is just plain wrong. When I was looking at 2003 390 Mainships this was always something you had to look out for.
John
2003 MS 390

BruceK said:

You might want to check the exhaust raw water injection point. Based on solid advice from others here, it was a real issue on turbo Yanmar 4cyls, potentially leading to standing water affecting risers/angles and turbos. ? affects 6cyl versions.

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Common problems with Yanmar in Mainships and other boats. The problems were due to installation issues. Because the 4 cylinder Yanmar is a low profile engine it was easy to stuff into small spaces which were low on the waterline. Yanmar recommendations a 13 inch rise from waterline to the spillover point of the exhaust elbow. I have seen installations where the rise was 1/2 that. (My own boat) This results in salt water intrusion through backflow from the exhaust. This caused damage to the turbo or worse. The builders were too cheap or did not leave space to install a proper riser. No fault of the engine.

Another common problem is people putting the wrong antifreeze in the engines which can cause cavitation damage in the exhaust manifold. Again user error.

Easting said:

Common problems with Yanmar in Mainships and other boats. The problems were due to installation issues. Because the 4 cylinder Yanmar is a low profile engine it was easy to stuff into small spaces which were low on the waterline. Yanmar recommendations a 13 inch rise from waterline to the spillover point of the exhaust elbow. I have seen installations where the rise was 1/2 that. (My own boat) This results in salt water intrusion through backflow from the exhaust. This caused damage to the turbo or worse. The builders were too cheap or did not leave space to install a proper riser. No fault of the engine.

Another common problem is people putting the wrong antifreeze in the engines which can cause cavitation damage in the exhaust manifold. Again user error.

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Easting (and others),
The exhaust install issue is a common problem with many boats and many engine brands. When looking to purchase, this is an issue that should be considered as the costs of ignoring (or just not knowing) could be very large! (worst case - new engine). Replace these exhaust setups with improved "custom" setups where possible, and avoid boats where it is not (when purchasing). Ensure your mechanic pulls the exhaust and check the exhaust side of the turbo as part of your survey and factor in the findings in either price or in your buy (or no buy) decision.

Fanbois debate?

Delfin said:

Talking to a CAT engineer who helped in the initial design of the motor, and whose experience with it on the North Slope exposed him to genset applications that got that many hours without much difficulty. Those number of hours translates to around 2.5 million miles on a truck engine, which is strong mileage, but not that unusual. By the way, since Yanmar makes industrial engines, any thoughts on why you never seem to see one in an 18 wheeler, bulldozer, etc? Maybe there are some, but they seem kind of rare.

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Ok, this is starting to sound like a fanbois debate, not much different from debating politics or religion.

The question Jeff and Deb asked was about the >>available<< engines in a Mainship single engine configuration.

There are ONLY three choices, Cat3116/3126, Cummins 6BTA and Yanmar 6LYA.

Of these three, the Cat 3116/3126 engines have a bad reputation -- especially in marine propulsion. That doesn't mean that that whatever flaws they had or have can't be fixed. It just means that of the three choices, the 3116/3126 have a bad reputation, and the resale prices of Mainships with these motors reflect that. The problems with the 3116 and 3126 are widely known and don't need re-hashing here. Let it suffice to say that if you are buying a Mainship with a 3116/3126, you need to be careful and know what the specific risks are associated with these engines.

I'm not a fanboy. I think Caterpillar makes many great engines, but they've made some real stinkers too. I'm sure the same is true of Cummins and Yanmar, but the 6YLA and the 6BTA are widely regarded as "among the best" of the Yanmar and Cummins breeds. I don't think any knowledgable Caterpillar person will tell you the 3116/3126 engines were anywhere near the top of the heap in the Cat lineup. Most caterpillar people (including the big rebuilders) agree that these were among the worst Cat motors made.

http://www.capitalremanexchange.com/best-diesel-engine-list/

The Caterpillar 3126 Engine

https://www.yachtforums.com/threads/class-action-lawsuit-bought-against-caterpillar.6341/

https://www.capitalremanexchange.com/best-diesel-engine-list/

Delfin's Caterpillar 3208's might be a great engine, but since these are not among the choices for Mainship buyers, they are not relevant in this thread.

re: "any thoughts on why you never seem to see one (Yanmar) in an 18 wheeler, bulldozer, etc?"

Sounds like a purely rhetorical question, but maybe I'm wrong, so I'll try to answer.

1) It may have something to do with the fact that Yanmar has never tried to enter those markets. Since 1912, Yanmar have focused on the small engines markets. Meanwhile, Caterpillar no longer makes any marine propulsion engines less than 6-cylinders or less than 7 litres.

2) Or it may have something to do with vertical integration...and the fact that the major manufacturers of semi-trucks and heavy construction machinery (like Caterpillar) are also their own engine manufacturers.

3) Or maybe it's because Yanmar is more focused on Marine and small-engine applications overall. Perhaps this is why you never see a Caterpillar (or Cummins) engine on a saildrive?

Lastly, 50,000 engine hours achieved in a landside genset application (on the North Slope or anyhere else) have absolutely nothing to do with hours in marine propulsion applications. For most of us, this will be obvious so I won't go into details.

firehoser75 said:

Ensure your mechanic pulls the exhaust and check the exhaust side of the turbo as part of your survey and factor in the findings in either price or in your buy (or no buy) decision.

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As nice as it sounds, tearing engines down for a pre purchase survey is not common. I wouldn't allow an unknown wrencher to do anything on my vessel during a survey except to take oil samples - and often these are done wrong.

A good engine guy (and many surveyors) can spot a haywire exhaust riser layout in a second while noting other mechanical visuals. Coupled with sea trial and a review of maintenance records that is largely the mechanical inspection.

Any problems found can then become a further discussion.

I have found the 3116/3126 to fare poorly if they have to run hard to do the job. Like running cruise at 2400 with top end 2800. In some applications, the boat runs great at 2100 and under, and there it can really shine. This applies to the 3116 at 350hp and 3126 at 420. There are lower ratings out there that can run harder. Been involved in several local 31XX series that have "popped" (usually a piston or valve problem) when run hard. Also the injection system takes some elaborate tooling to properly set, and few mechanics are so equipped.

The Yanmar 6LY is a nice engine, about the only complaint I have is the aluminum exhaust manifold and sea water oil cooler. Very few in memory have "popped". Some wrecked by overheat or water ingestion or bad coolant rotting the manifold. Or corroded steel oil lines (WTF?).

6LY2 has the hardened bores to get more diameter, I don't recommend those. Not very repairable.

The 6BT and 6BTA have a very good reputation. There are some weak spots depending on the model rating, but with a little common sense these can be handled. Not as compact a layout as the Yanmar (kudos to them there), but you can get to everything and parts are much less expensive. No aluminum in cooling system on the Cummins!!

All three brands can do the job very well, provided you understand the weak spots and apply common sense regarding maintenance and operation.

Riverguy said:

3) Or maybe it's because Yanmar is more focused on Marine and small-engine applications overall. Perhaps this is why you never see a Caterpillar (or Cummins) engine on a saildrive?

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Or perhaps because they don't make one, unlike Yanmar that makes engines with sufficient hp to power a Kenworth. Yet, no truck mfg uses them, at least in the US...

Riverguy said:

Lastly, 50,000 engine hours achieved in a landside genset application (on the North Slope or anyhere else) have absolutely nothing to do with hours in marine propulsion applications. For most of us, this will be obvious so I won't go into details.

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You're right, it isn't apples to apples. Gensets run at continuous rpms, and if designed for the North Slope, have to be able to run at very low loads for long periods. In other words, kind of like a boat.

I was at the CAT dealer yesterday to get filters and asked the service manager if he had seen 50,000 hours out of a 3306 in a truck and he said, no, 40,000 without being touched was the max he had seen.

But you don't really need to defend Yanmar so emphatically. It's a great engine and will last as long as most people need a marine diesel to run. And you're right, the 3116 and 3126 are probably the most finicky engines CAT made, but assuming one in a Mainship doesn't have the known issue of French cast blocks, and assuming the POs have used the oil CAT specifies, my guess is that the 3126 CAT will outlast the Yanmar 2:1, minimum. Heavier, slower turning, higher displacement than the Yanmar - it is kind of what you would expect.

Caterpillar recall mythology?

johnma said:

This has already been said, buy I didn't want it to get lost in the other discussions. For Mainship the recommended engine is the Yanmar or cummins. Cat did in fact have issues with the 3116/3126 blocks built in France and they did have a recall on them. Whether the boat you look at has had it replaced or not should be a concern. For the seller to say the 3126 is recommended is just plain wrong. When I was looking at 2003 390 Mainships this was always something you had to look out for.
John
2003 MS 390

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Thanks John, I totally agree.

Re: "Cat did in fact have issues with the 3116/3126 blocks built in France and they did have a recall on them..."

I have heard this too -- that Caterpillar did a general recall, but I personally saw two of them (based on the code on the casting) when I was looking at used 350/390's in 2011-2013. The code was cast into the block, and the Caterpillar dealer I called told me they couldn't tell from the serial numbers.

Now, I also heard that the whole 'general recall' story was a myth propagated by Caterpillar and their dealers...

My understanding is that Caterpillar replaced blocks that failed within the first 1,000 hours, and they replaced some others when the customer demanded it, but that there was never a 'general recall'. Customers did not get a letter or any proactive notification, and so the rest of the French blocks are still out there.


Does anyone have any hard evidence of a general recall?

Here's the thing....it has always seemed bizarre to me that somehow, Caterpillar could not tell folks if they had a defective block from France just based on the engine serial number. It is completely unbelievable that somehow Cat just unloaded these French blocks from the shipping containers, dumped them into their assembly plants, mixed them in with the domestic blocks inventory and didn't keep track of which engine S/Ns got the French blocks! That's not how manufacturing or Q.C. works. Back in the early '90's, Caterpillar made a huge deal about being one of the first ISO 9000 certified manufacturers in the U.S., so when they say "we can't tell by the serial number", it stinks to high heaven.

Re: "Whether the boat you look at has had it replaced or not should be a concern."

Exactly, but how do find out for sure if Caterpillar can't tell you if your engine has a French block or not, either as an original or not? AFAIK, Caterpillar is also saying that (somehow) they haven't kept track of which engine serial numbers got new blocks.


I feel bad for all the boat owners with Cat3116/3126 motors who are suffering from crappy resale value because Caterpillar won't come clean.



CAT 3126 Oil Consumption Issue? | Club Sea Ray

Ski in NC said:

I have found the 3116/3126 to fare poorly if they have to run hard to do the job. Like running cruise at 2400 with top end 2800. In some applications, the boat runs great at 2100 and under, and there it can really shine. This applies to the 3116 at 350hp and 3126 at 420. There are lower ratings out there that can run harder. Been involved in several local 31XX series that have "popped" (usually a piston or valve problem) when run hard. Also the injection system takes some elaborate tooling to properly set, and few mechanics are so equipped.

The Yanmar 6LY is a nice engine, about the only complaint I have is the aluminum exhaust manifold and sea water oil cooler. Very few in memory have "popped". Some wrecked by overheat or water ingestion or bad coolant rotting the manifold. Or corroded steel oil lines (WTF?).

6LY2 has the hardened bores to get more diameter, I don't recommend those. Not very repairable.

The 6BT and 6BTA have a very good reputation. There are some weak spots depending on the model rating, but with a little common sense these can be handled. Not as compact a layout as the Yanmar (kudos to them there), but you can get to everything and parts are much less expensive. No aluminum in cooling system on the Cummins!!

All three brands can do the job very well, provided you understand the weak spots and apply common sense regarding maintenance and operation.

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Ski, that is what I have heard as well with respect to trying to get long hours out of the 31x6 motor. Not hard if the engine is run with a fractional load factor but not so much if run flat out most of the time. I can't remember the details, but I am pretty sure that I saw an image of where to look on the block to see if it had one of the soft ones made in France. Can you confirm that?

Finally, the Yanmar 6lpa I had ran well but smoked like crazy - to the point where I had to avoid starting it if anyone was on the dock nearby. The Yanmar tech told me that it was pretty normal for that engine, and I could never get rid of the problem. This post refers to a known problem with all of these engines made during certain years regarding the valves, and it sounds like it might have been the source of the problem with mine. Have you dealt with this issue?

https://www.justanswer.com/boat/6ppdf-problem-yanmar-6lpa-stp-stzp-315-hp-motors.html

7 years ago, I was in your shoes when I was in the process of purchasing my Mainship 390 and wondering/researching which engine option to prefer. My research (speaking to MS390 owners as well as diesel manufactureres) led me to the conclusion that I would probably be happy with any of the 3 options. This was because most of the owners of the various engines available (CAT, Cummins, Yanmar) were generally very happy with what they had chosen regardless (including 3116 owners).
The diesel manafacturers reps that I spoke to all admitted to having had recalls on various products through the years. Caterpillar is not alone, just google Yanmar 6LP valve issues!
There are a couple of misconceptions that are being propagated here. I don't think the 3126 was affected by the soft French block issue. That was the 3116. These 2 motors are similar, but not the same.
Another point to make is that the soft French block motors have all worked their way out of the market. Those motors failed at about 500 hours. If you are looking at an 18-20 year old boat that has less than 500 hours on it, RUN! no matter which diesel manufaturer it has. 500 hours in 20 years is 25 hours a year. Such a boat is not being used enough to stay healthy. Are they changing the oil every 10 years, because the maintenance interval on these motors is 200-250 hours?
In a previous post, someone linked to a board with a 1996 Trojan owner complaining about CAT 3126s. The 3126 was introduced in 1997. Hmmm. I wonder how that works.
CAT makes more diesels than anyone else and their support and parts distribution is largest. Keep this in mind.
Also in a previous post, engine weights and displacements are discussed. This is certainly something to think about. The CAT bashers failed to mention that the CAT3126 has the highest displacement and is the heaviest motor of them all and it stands to follow that it will be the most relaxed pushing your new MS390 along at whatever speed you choose to cruise.

Get the Mainship 390 that you want with the motor you want and ignore the naysayers. Just make sure it has been well maintained.

rendern said:

7 years ago, I was in your shoes when I was in the process of purchasing my Mainship 390 and wondering/researching which engine option to prefer...

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Lots of what you say makes sense, but you are mistaken in a number of areas:

1) Cat 3126 motors most definitely were affected by the bad "french blocks", as were the 3116's. Numerous posters here have provided links. FYI, 3126 and 3116 were both introduced in 1995 (links with proof are below).

2) Yanmar may have had problems with the 6LPAs (can you provide a link?), but since they were not introduced until 2008, none of these ever went into any MS350/390, which was only made until 2004. So, this is not relevant to someone who is looking for a MS350/390. Link here: Yanmar delivers SOLAS compliant engine - Marine Business

3) Re: "Another point to make is that the soft French block motors have all worked their way out of the market."

NO! This is a widely propagated myth, and no one has ever been able to substantiate it. Many of us would like to have any kind of proof to confirm this. Since this debacle began in 1999-2000 timeframe, no Caterpillar 3116/3126 OWNER has ever reported being notified that their block was going to be replaced, nor has anyone ever seen a recall letter. The idea that "these have worked their way out of the market" is mere speculation. The only thing we know is that Caterpillar replaced many failed blocks.

4) Re: "someone linked to a board with a 1996 Trojan owner complaining about CAT 3126s. The 3126 was introduced in 1997. Hmmm. I wonder how that works...".

That was me, and you're mistaken. The Cat 3126 was introduced in 1995, not 1997. Among the hits you will see in the Google search below is tha Consent Degree signed by Caterpillar showing these engines were introduced in 1995. Thousands of other links are out there as well. I've added a .jpg for reference.

Don't trust Wikipedia -- 98% of the people who go there to write stuff about things like engines are 'brand-fanboys' for one engine or another, and generally know nothing.

https://www.google.com/search?q="caterpillar"+"3126"+"1996"+filetype:pdf

Bottom line -- Of the three engines that Mainship used in the single-engine 350/390, the Caterpillar 3116/3126 had BY FAR the most problems, and it wasn't all about "French Blocks". The 3116 and 3126 were among Caterpillar's first 'disposable' engines (Parent-Block design) -- meaning they were intended to be trashed when the cylinder liners wear out. Both the Yanmar 6LYA and the Cummins 6BTA are 'sleeved' engines, meaning that the cylinder liners can be replaced 'in-frame' without pulling the engine and taking it to a specialized machine shop. This means that rebuilding a 3116/3126 that needs cylinder liner(s) is more expensive than the engine is worth.

https://www.google.com/search?q="parent+block"+"3126"

As I and many have said, Caterpillar have made some fine engines for marine applications -- but the 3116 and 3126 are not among them. This is why boats that have them sell for 10-15% less than Yanmar/Cummins equipped boats.

OK, Riverguy...here we go.

Lots of what you say makes sense, but you are mistaken in a number of areas:

1) Cat 3126 motors most definitely were affected by the bad "french blocks", as were the 3116's. Numerous posters here have provided links.*FYI, 3126 and 3116 were both introduced in 1995*(links with proof are below).

***No poster has provided ANY proof that the 3126 was affected. Only links to boards like this one with semi-knowledgable folks spouting opinions (like you and I). *****

2) Yanmar may have had problems with the 6LPAs (can you provide a link?), but since they were not introduced until 2008, none of these ever went into any MS350/390, which was only made until 2004. So, this is not relevant to someone who is looking for a MS350/390. Link here:*Yanmar delivers SOLAS compliant engine - Marine Business

**** https://www.justanswer.com/boat/6ppdf-problem-yanmar-6lpa-stp-stzp-315-hp-motors.html - Again, this is just a board with semi-knowledgable folks.*****

3) Re:*"Another point to make is that the soft French block motors have all worked their way out of the market."

NO! This is a widely propagated myth, and no one has ever been able to substantiate it. Many of us would like to have any kind of proof to confirm this. Since this debacle began in 1999-2000 timeframe, no Caterpillar 3116/3126 OWNER has ever reported being notified that their block was going to be replaced, nor has anyone ever seen a recall letter. The idea that "these have worked their way out of the market" is mere speculation. The only thing we know is that Caterpillar replaced many failed blocks.

4) Re:*"someone linked to a board with a 1996 Trojan owner complaining about CAT 3126s. The 3126 was introduced in 1997. Hmmm. I wonder how that works...".

That was me, and you're mistaken.*The Cat 3126 was introduced in 1995, not 1997. Among the hits you will see in the Google search below is tha Consent Degree signed by Caterpillar showing these engines were introduced in 1995. Thousands of other links are out there as well. I've added a .jpg for reference.

Don't trust Wikipedia -- 98% of the people who go there to write stuff about things like engines are 'brand-fanboys' for one engine or another, and generally know nothing.

**** None of my info or comments are sourced from Wikipedia ****

https://www.google.com/search?q="c...filetype:pdf

Bottom line -- Of the three engines that Mainship used in the single-engine 350/390, the Caterpillar 3116/3126 had BY FAR the most problems, and it wasn't all about "French Blocks". The 3116 and 3126 were among Caterpillar's first 'disposable' engines (Parent-Block design) -- meaning they were intended to be trashed when the cylinder liners wear out. Both the Yanmar 6LYA and the Cummins 6BTA are 'sleeved' engines, meaning that the cylinder liners can be replaced 'in-frame' without pulling the engine and taking it to a specialized machine shop. This means that rebuilding a 3116/3126 that needs cylinder liner(s) is more expensive than the engine is worth.

**** Where to begin....

"Bottom line -- Of the three engines that Mainship used in the single-engine 350/390, the Caterpillar 3116/3126 had BY FAR the most problems" - based on what!? ...Your opinion.

**** And this...

" and it wasn't all about "French Blocks" - OK, what else is wrong with them?

**** And here's where some schooling is warranted...

"The 3116 and 3126 were among Caterpillar's first 'disposable' engines (Parent-Block design) -- meaning they were intended to be trashed when the cylinder liners wear out. Both the Yanmar 6LYA and the Cummins 6BTA are 'sleeved' engines, meaning that the cylinder liners can be replaced 'in-frame' without pulling the engine and taking it to a specialized machine shop. This means that rebuilding a 3116/3126 that needs cylinder liner(s) is more expensive than the engine is worth."

- Flat incorrect. ALL of the above listed motors are parent bore. 3126, 6LYA and 6BTA. Period. None of these motors have wet sleeves or cylinder liners. None of them are "throwaways" either. The blocks of all of them can be removed from the boat and bored out and dry sleeved. This can be done for much less than the cost of a new diesel engine.

Wow!! Lots of facts and fiction going back and forth above. Let me disprove the following misstatement with an attached pdf page from the Yanmar 6LYA parts manual showing a cylinder liner- item 26. Can we believe any of the "facts" stated above?

David

"Flat incorrect. ALL of the above listed motors are parent bore. 3126, 6LYA and 6BTA. Period. None of these motors have wet sleeves or cylinder liners. None of them are "throwaways" either. The blocks of all of them can be removed from the boat and bored out and dry sleeved. This can be done for much less than the cost of a new diesel engine."

Side comment but I have to take exception with this repeated claim that one should RUN from a low hour engine. Lots of us live in Northern climates (including Riverguy at some point). We have 4 months where you have a good shot at boating, particularly if you work for a living and can only get out on weekends. 500 hours over 20 years of 4 month seasons is plenty of time to get up to operating temperature every time, I can assure you. If I cruise a few hours out to my favorite island, anchor for the weekend and dinghy around, and cruise back I don't put on a lot of hours. But that certainly doesn't mean that I don't check and maintain the engine.

Moreover, these boats are winterized every year, which for anyone who has their engines maintained professionally always includes an oil change, regardless of hours. My oil is clean as new every season but it gets change anyway. Also for many of us Northerners, the usage is in fresh water which is far less corrosive in "marine hours" regardless of engine hours.

Especially as someone who has a super well maintained, low hour boat on the market right now, I find these claims to "run away" as silly.
BD

djmarchand said:

Wow!! Lots of facts and fiction going back and forth above. Let me disprove the following misstatement with an attached pdf page from the Yanmar 6LYA parts manual showing a cylinder liner- item 26. Can we believe any of the "facts" stated above?

David

"Flat incorrect. ALL of the above listed motors are parent bore. 3126, 6LYA and 6BTA. Period. None of these motors have wet sleeves or cylinder liners. None of them are "throwaways" either. The blocks of all of them can be removed from the boat and bored out and dry sleeved. This can be done for much less than the cost of a new diesel engine."

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OK djmarchand, I'll split this one with you. The sleeve in that drawing is a dry sleeve, which some would argue is hardly different than parent bore. I was talking about "wet sleeves" (I indicated as much) which is a whole different game. Good catch though and you deserve points.

Riverguy said:

Both the Yanmar 6LYA and the Cummins 6BTA are 'sleeved' engines, meaning that the cylinder liners can be replaced 'in-frame' without pulling the engine and taking it to a specialized machine shop.

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The 6BTA (e.g., 5.9) is not sleeved; the 6CTA (8.3) is.

-Chris