How many hours can an engine last ?

[gulfislandfred]

With a sail drive, it doesn't matter how long the motor lasts. The sail drive will be shot in a season or two


Most pleasure boat engines die from lack of use and lack of maintenance. Very few get enough hours of use to wear down the rings and bearings.


Different brands of engine are more or less durable.
My top picks are Isuzu, Kubota/Universal, and Yanmar, in that order. Lehman and Perkins for 40 hp and bigger, but lower on the list than the first three.
I've owned, maintained, and repaired all of the above.
I would always prefer naturally aspirated to turbo, for fuel economy and longevity.

[bilgolabands]

If that 55hp Volvo is the Perkins based engine 6000 hours is very acceptable. One in our marina has 8700 hours and with good service and attention to the heat exchanger the owner has no fears re. his motoring future
Bilgolabands

[Tillikum]

With clean oil of the right weight kept at the correct pressure and clean fuel an engine can last decades.

"Clean" in that sense means sub-micronic filtration via a centrifugal oil "filter".

Why change oil when it is only dirty, not "worn out"? Instead of the sawtooth graph of oil cleanliness and engine wear which results in the typical run-change-run-change type scenario, keep the oil as clean as new all the time and there will be almost no engine wear.


Such filters can also remove water/condensate.

[merrydolphin]

Higher reving engines tend to go 9-12,000 hrs. Slower ones can go over 20,000. Eg, the older Perkins. My last boat had a Perkins 4-236 and when I sold it with around 20,000 hrs. The buyer took it from Cabo to HI to Vancouver, to S Pacific and back to Vancouver. Same engine on a heavy cruising boat. And the boat carried 270 gals of diesel so it go used! All he did was upper end, valves etc. a lot has to do with how it’s used. If you mainly use it just to get in and out of harbor. You may only get 5K or so hrs. But if you USE it to cruise, much better on it. This is all considering good maintenance of course. The boat before, a KP 44, had a Perkins 4-154. I bought to boat with 4300 hrs and worried that it was a lot. I sold the boat 8 yrs later with over 10K hrs. The buyer had a Perkins man do engine survey with analysis and said the engine showed as an engine with 10K hrs and with the same maintenance it had been getting could go another 10K.

[icemate]

Originally Posted by henris

Hello,


I am planning to buy a sailboat with a volvo-penta 55HP engine with a saildrive. The motor is running fine and was apparently well maintained. But... it has more than 6000h.
Should I consider it is at its end ?
What is a reasonable amount of hour to consider the replacement of the motor ?
What are the alternatives ?

I had a volvo penta on a tayana. Great boat , lousey motor and transmission. The volvo as I was told while sailing in the Pacific by someone who had worked for volvo told me it was a marinized Tractor engine. After having trans rebuilt 3 times I replaced the with a Yanmar. Cleaner, lighter, quieter, better mileage. Negotiate the price to allow replacing the moter.

[daveandsara2016]

When I purchased my boat last year, the surveyor said my Volvo Penta 55hp motor has a life of 10,000 hours.

[Icarus]

A well maintained diesel engine on a boat can easily last 10.000 before a rebuild is warranted.
ISome truck engines have a million km on it

[Dockhead]

Originally Posted by gulfislandfred

. . . I would always prefer naturally aspirated to turbo, for fuel economy and longevity.

Little quibble here -- naturally aspirated diesels may have better longevity than turbos on motorboats with planing or semi-displac hulls which are used at high power outputs for long periods of time.


But for sailboats and trawlers, which are usually operated at fairly small percent of maximum power, turbo engines will generally last longer, because they are better loaded in their usual operating regime with better cylinder temp.


Turbos are almost always more, not less fuel efficient, than naturals. On the boost, they are recuperating energy which would otherwise be lost out the exhaust. Off boost they are more efficient than naturals of the same horsepower rating and greater displacement, because less friction. But the differences are not large; almost all small four stroke diesels have efficiency in a fairly narrow range.

[gulfislandfred]

I appreciate the comments about turbos.
I will freely admit to a prejudice in favor of simpler machinery that runs at lower RPM.

Could you please elaborate on how a turbo engine, off boost, has less friction? It seems counter intuitive that an engine with more parts will have less friction.


My main issue with turbo engines is breakdowns. From old 5 cylinder Mercedes cars, to engines on modern yachts, my observation (purely anecdotal) is that the turbo components fail more often than the rest of the system. This may be due to long periods of inaction, and minor corrosion in the turbo bearings, in the salt air, that leads to problems as the cycle repeats over a few years.


2 stroke Screaming Jimmy diesels seem to have less turbo issues than more modern engines. Again, anecdotal input from one biased observer

[rslifkin]

Originally Posted by gulfislandfred

Could you please elaborate on how a turbo engine, off boost, has less friction? It seems counter intuitive that an engine with more parts will have less friction.

For a given power output, the turbo engine will be smaller displacement. So smaller pistons and cylinders, shorter stroke, etc. That all leads to less friction and also lower pumping losses to move air through the engine. There's a reason that outside of fairly small engines, most diesels are turbocharged at this point. It gives a significantly better power vs size/weight relationship and also improves efficiency.

[gulfislandfred]

Thanks,
I hadn't thought of smaller engine, more power extracted.


That would mean higher rpm for equal power output?
My prejudice toward things that move more slowly jumps in here. The sound and vibration of higher rpm bothers me. I can get used to it (have done, with 53 series GMs on salmon trollers, back when dinosaurs walked the earth. It sure felt good when we got back to the dock and shut off the engine, though.)



I like bigger engines that I can run at well below their rated horsepower, to get hull speed, or a bit less than hull speed, in a displacement hull. There are times when the extra power is good to have. (I like to play tug boat) I do crank it up for an hour now and then to burn out the carbon.
I think fuel efficiency is as good or better with with my heavy old engine, running at maybe 1500 to 1800 RPM.

[rslifkin]

Originally Posted by gulfislandfred

Thanks,
I hadn't thought of smaller engine, more power extracted.


That would mean higher rpm for equal power output?
My prejudice toward things that move more slowly jumps in here. The sound and vibration of higher rpm bothers me. I can get used to it (have done, with 53 series GMs on salmon trollers, back when dinosaurs walked the earth. It sure felt good when we got back to the dock and shut off the engine, though.)



I like bigger engines that I can run at well below their rated horsepower, to get hull speed, or a bit less than hull speed, in a displacement hull. There are times when the extra power is good to have. (I like to play tug boat) I do crank it up for an hour now and then to burn out the carbon.
I think fuel efficiency is as good or better with with my heavy old engine, running at maybe 1500 to 1800 RPM.

Depending on the design, how the turbo is sized, etc. it may mean higher RPM or it may not. There are some fairly low revving turbodiesels out there as well as high revving ones.

Smoothness, vibration, and sound depends a lot on the engine design, installation factors, etc. not just RPM. For example, a 6 cylinder Cummins B series is much smoother than the 4 cylinder version with both turning the same RPM.

In many cases, an engine with smaller cylinders turning faster (less power needed each time it fires) will produce higher frequency noise and vibration, which is easier to muffle (from the exhaust as well as with sound insulation and vibration isolating mounts). So sometimes the higher revving engine is easier to quiet down when installed, even though the un-muffled noise from it may be more unpleasant.

More aggressively turbocharged engines are also less likely to suffer from under-loading, making them good for applications where you only need a fraction of the power most of the time, but occasionally need more. That's why highly turned up engines are so common in planing hulls. In that application you may need all of the power for a few seconds to shove the boat up onto plane, but once it's there, design cruise speed may only require 60% of the engine's output (so despite the engine being pushed pretty hard at WOT it never spends much time there in real world use).

[Dockhead]

Originally Posted by gulfislandfred

. . . Could you please elaborate on how a turbo engine, off boost, has less friction? It seems counter intuitive that an engine with more parts will have less friction.. .

Less displacement equals less friction, less swept area, smaller bearings, etc.

Example -- my boat could be ordered with either a Yanmar 4JH3 HTE 100hp, 2000cc turbodiesel, or a Perkins M92 natural.

Yanmar makes 100hp, Perkins 83hp.

Yanmar 2000cc, Perkins 4400cc.

At any given RPM, the Perkins is pumping 2.2x as much air as the Yanmar off the boost. It will have much cooler cylinder temp at low power settings which is bad for longevity, and will be making more friction.

The Perkins makes up for it partially with lower RPM for a given output, and by being build like a brick outhouse. But for that reason, it weighs 400kg, nearly half a ton -- without the marine gear (!). The Yanmar -- 228kg.

As to trouble -- different engines are different. Beta, Nanni, and Yanmar have good reputations. Volvo mixed. Turbochargers, at least those without wastegates, have only one moving part. I had mine rebuilt when I bought my boat 15 years ago -- it cost less than a boat buck; it takes 20 minutes to take the turbo off the engine. Not the slightest problem with it 4000 hours later.

[gulfislandfred]

Thanks Dockhead,
I'm learning from this discussion. I've never had a planing boat big enough to warrant a diesel, so lighter weight is not a concern.


Don't think there's anything over 30 feet in my future.
I'm a big fan of the 4 stroke Yamaha/Suzuki outboards. Lots of high end power for fast boats. As you say, throttle back on plane, and they're not hard to live with. Same engines with reduction gear work well on heavy stuff.
You haven't mentioned Isuzu engines. Any opinion?
They seem to have a good reputation.
I have recently acquired a Fisher 30 with a 4cyl Isuzu. After a new supply pump, and rebuilt injectors and injector pumps (1 per cylinder) it's running well, after maybe 10 years idle and neglected. It was in the boat, and able to be made to run.

[Cheechako]

Turbos today are used to squeeze more HP out of a smaller lighter engine. Longevity wise it's a deficit as a general statement. But there are a ton of "if ands and buts". Not sure one can say a faster rpm engine eeking all the hp it can out of a small format has less friction per hour as it's cycling far more revolutions.
It's a known thing in larger diesel engines that higher rpms wear engines faster, again a general statement.
Large diesel engine sellers actually reduce the specified RPM on Continuous Duty commercial applications and raise the specified RPM on Recreational use application FOR THE SAME ENGINE! So a Fishing boat engine may be specified for 2400 rpm and a Rec boat engine at 3200 rpm.