Engine Hours

I'm searching for a 40 to 50 ft trawler. All of my experience is with gasoline engines. Looking at a few mid-2000's boats. At what point should I start getting concerned about the number of hours on the engines? I'm seeing some in the 1,000 to 1,500 range and others in the 3,500 to 4,500 range. Unfortunately the boats that I like are on that higher end. When would you walk away just based on engine hours?

For example, one is a Grand Banks, Caterpillar engines, 3,200 hours. Another is a DeFever CMY with over 4,000 hours. It seems that the prices are somewhat taking into account the number of hours in comparison to other listings but not dramatic discounts.

I guess that at some point the engines need to be re-built? What does that entail for a diesel?

Appreciate any thoughts on this.

Frank60 said:

I'm searching for a 40 to 50 ft trawler. All of my experience is with gasoline engines. Looking at a few mid-2000's boats. At what point should I start getting concerned about the number of hours on the engines? I'm seeing some in the 1,000 to 1,500 range and others in the 3,500 to 4,500 range. Unfortunately the boats that I like are on that higher end. When would you walk away just based on engine hours?

For example, one is a Grand Banks, Caterpillar engines, 3,200 hours. Another is a DeFever CMY with over 4,000 hours. It seems that the prices are somewhat taking into account the number of hours in comparison to other listings but not dramatic discounts.

I guess that at some point the engines need to be re-built? What does that entail for a diesel?

Appreciate any thoughts on this.

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I am generally ignorant about all things related to engines, so I won't try to answer your question. However, the article below I think does a good job of addressing some aspects of your question and may be a good place to start thinking about it.


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

That sbmar article is a good start. Most marine diesels fail due to lack of maintenance of the marine parts, not the core engine. And even a badly taken care of engine can get a full marinization rebuild for a fraction of the cost of a replacement engine and you don't have to pull the engine to do it, just replace external stuff like the main heat exchanger and after cooler. But that only works if salt water hasn't gotten to the core engine.

So look at how the engine has been cared for. You can trash the marinization stuff in 1,000 hours and it can ruin the core engine or you can maintain it properly and it will be good for 10,000+ hours.

One way to tell how an engine has been cared for is to look at the zincs on the main heat exchanger. If they are gone, well probably nothing has been done in ages to the rest of the marine parts.

David

It really depends on the engine. 4000 hours on a 270hp DD671 is nothing. 2500 hours on a 480hp DD671 is too many.

Care and usage are far more important than meter hours. Run 'em hot and hard and they won't last long. Run 'em easy keep up on the maintenance use them regularly and 4000 hrs isn't anywhere near the life span. Run them rarely and ignore routine maintenance or perform it on engine hours alone and they will have a short life span in meter hours. In other words there is no firm answer.

For a rough idea on overhaul costs, and keep in mind this is a very rough idea, use $2,000 per cylinder for a diesel. Yes, I know, a lot here are going to debunk that rough estimate. Keep in mind it is a rough number but I did get it from a life long boat diesel mechanic I trust. I found it a good place to start rebuild estimates on work boat engines. That does not include the costs of removing and re-installing if there is not sufficient access in the engine space on the boat.

Next if you're considering a boat that may need rebuild look at age of the engine in calendar years which affects parts availability and finding mechanics that are familiar with the age engine you are considering rebuilding.

I think the best approach is to find a good mechanical surveyor. Make absolutely certain he gets to witness a cold start. That is the engines have not been run for at least 24 hrs, longer is better. Oil samples are nice but not all that great unless done on a regular basis to establish trends. A lot of the time you will find a boat listed for sale has had the engine oil changed recently so you're sampling fresh oil. A nearly useless effort.

For a rough idea on overhaul costs, and keep in mind this is a very rough idea, use $2,000 per cylinder for a diesel. Yes, I know, a lot here are going to debunk that rough estimate.

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I would agree with that "assuming" the add on parts like heat exchangers, manifolds, etc are in reusable condition.

I will try to explain engine life. First we have to assume no damage was ever done to the engine. 1 overheat and that could add 3000 hrs. to a head. Suck in seawater by way of turbo and you can kill it quick. Don’t service a intercooler and you can kill the rings. But suppose these things never happened? Then it’s all about burning fuel. A light duty diesel will burn 70,000to 150,000 gallons before any significant overhaul. It doesn’t matter much how you burn it as long as you never overload the engine and stay in the operating range. So if the boat runs at 1,400 rpm for 20,000 hours that might be the same as running 2,400 rpm for 5,000 hours. [ just an example. ] proper calculations can be made if you have the ships log. Therefore hours by themselves mean very little.
I have serviced Deere’s with 38,000 hours and never touched the guts. I have also condemned a yanmar with 1,700 . Not the fault of the engine, but more the operator.

.50-.75 horsepower per cubic inch on a well maintained (more than just oil and filter changes) diesel should give you between 15-20,000 relatively trouble free hours before needing a rebuild. The oid Detroit’s in naturally aspirated form are very reliable engines and can generally go past 20k hours and still have reasonable compression. Start going past 1-1.2hp per cubic inch and life expectancy is generally greatly reduced. 2hp+ per cubic inch engines are generally grenades that require rebuilds between 1500-3000 hours and even before rebuilds they usually have big ticket expensive things that brake constantly, also the blocks generally only have 2-3 rebuilds in them before the block is bad, the blocks will literally stretch and go out of spec so you can’t put in new sleeves The low hp-cubic inch engines can generally be rebuilt almost indefinitely . Keep this in mind this is generally true. But there are exceptions to the rule, and a lot of it has to do with how the boat is ran through its life. That’s why it’s important to have maintenance records, also generally a good idea to talk to the mechanic who fixes and services the engine on a regular basis, if he is good he will be able to tell you how the boat is ran on a regular basis as well as if the maintenance has been done properly. So far the best engine I have seen yet in a boat is a jd6068, I’ve seen a 275hp pair hit 43,000 hours without ever having the heads off, in that time one took 3 idler pulleys, one water pump, and valve adjustments every 5,000 hours. The other just the 3 idler pulleys and valve adjustments. They were both keel cooled btw. After one week of use you would need to turn them off and they would both take 1 gallon of oil. Compression was still acceptable and they did not smoke at all, so high hour engines properly maintained can go a long long time, and generally the newer the engine designe the less maintenance is needed... generally. Pretty much most things designed after the late 70s in low hp forms are fairly reliable. I’ve also seen brand new engines grenade within a couple months. And I’ve seen brand new rebuilds last 2 min.

Arc is correct on the fuel burn stuff but for a non mechanic or improper log keeping that’s much harder to calculate. Also in the lower hp ratings of engines they are generally 100% duty cycle engines meaning you can run them to the pins and still get high hours out of them. I’ve seen 12-71s in 500hp configuration last 25,000 hours and they were run to the pins for weeks on end sometimes.

But keep in mind that 12-71 even in 500hp trim that motor was still only at .58 hp per cubic inch.

That same motor run to the pins if it was 800hp+ would prob be a 3000 hour engine.

dhays said:

I am generally ignorant about all things related to engines, so I won't try to answer your question. However, the article below I think does a good job of addressing some aspects of your question and may be a good place to start thinking about it.


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

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If you go to sbmar.com, there's another article there to read, one on 'Marine Age', which is the effect of a saltwater environment on the life of an engine, even one with relatively few hours.

So the answer like everything related to boats is 'it depends'. As we all know, the challenge when buying a boat is you don't know how it was run. You can ask for records to see how it was maintained, but you likely don't get the whole story on a 15 year old boat with several owners. A survey can tell you only so much on the condition of the engine, but maybe that's all you have to go by.

I wasn't so much asking about the components that come in contact with saltwater: raw water pump, heat exchanger, aftercooler. Those are expensive to replace, for sure, but not nearly the cost of a rebuild or repower. That's what I was trying to figure out.

I guess this is a question that just can't be answered definitively. From the responses, it sounds like I shouldn't necessarily worry about 4,000 hours on a 7.2L, 450 hp engine as long as it was properly maintained.

Frank60 said:

I'm searching for a 40 to 50 ft trawler. All of my experience is with gasoline engines. Looking at a few mid-2000's boats. At what point should I start getting concerned about the number of hours on the engines? I'm seeing some in the 1,000 to 1,500 range and others in the 3,500 to 4,500 range. Unfortunately the boats that I like are on that higher end. When would you walk away just based on engine hours?

For example, one is a Grand Banks, Caterpillar engines, 3,200 hours. Another is a DeFever CMY with over 4,000 hours..

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Photo below - 1971 Perkins HT6-354 - 20,000hrs when I rebuilt it. It didn't really need a rebuild, I just had nothing to do one winter.

A 3208 natural at 220hp with 3500hrs is barely broken in. A 3208 turbo boosted to 425hp may well be in it's last stretch at 3,500hrs.

Oil analysis is your best bet for judging the condition of a used engine.

tiltrider1 said:

Oil analysis is your best bet for judging the condition of a used engine.

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With some significant caveats.
Oil_Analysis_on_Diesel_Boats

Both are potentially fine. Ask for maintenance records, look carefully at the engines for evidence of loving care & regular maintenance. CAT rates their longevity on gals of fuel burned, in keeping with previous posts. In general most diesels come in different HP ratings for a given block. Their duty cycle (how many hrs/day they can run full output) reflects their reliability with good maintenance. Unfortunately, the higher duty cycle versions give less HP/lb. everyone wants more speed so the more powerful versions (T, AC etc.) usually get ordered. My boat has JD6068T’s - 225 hp A silly upgrade since the extra HP can't help a 66,000 lb. boat. My 2004 had 4000 hrs on them when I bought her but full maintenance records so I decided to live with the whine & increased cost of the Turbo motors. Doing the math that’s only 2-300 hrs per year. Running at cruising speed, long coastal cruises, AICW etc. better for engines than sitting at the dock with occasional hard runs to the Gulf Stream. So most trawler style boats don’t plane so tend be run at around 1500-1700rpm +/-. Grand Banks are “semi displacement & many newer CPMY, have planing hulls. With higher HP engines, these boats are often run harder & faster unless the owner cared about fuel costs.
CAT turbo engines require significant ($$$) scheduled maintenance every 1500-2000 hrs. AfterCooler’s and Less used boats, more frequently.

tiltrider1 said:

Oil analysis is your best bet for judging the condition of a used engine.

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Maybe. Samples could show coolant in oil. But metal levels would mean nothing without 3 samples in a row with ample running time on each. Very impractical.

Not so much in my opinion. An oil sample taken from oil with, say, 100 hours on it that shows elevated metal level that would be highly indicative of bearing failure would certainly say a lot. Sure, you wouldn't have a trend but if those levels were really, really high one could very well draw a conclusion from the result. I would pass on a boat on which the oil was just changed unless the owner could show me a recent test.

Arc said:

Maybe. Samples could show coolant in oil. But metal levels would mean nothing without 3 samples in a row with ample running time on each. Very impractical.

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Oil samples are a useful, yet imperfect tool. I have reviewed hundreds of marine diesel oil analyses. Their value really varies with the type of engines. I have seen Detroit two strokes that had absolutely worn out liners and rings, yet perfect oil samples. I have seen Cummins with flagged (by the lab) high wear metal numbers, yet checked out perfectly and went on for several years of good service.

I tend to focus on Na and K (salt or coolant getting in oil), soot content (oil not changed enough), viscosity, fuel dilution, flags for glycol or water. The wear metals (Fe, Al, Cu, Pb, Tn, etc) get some attention, but these can be really skewed by lots of sitting time.

Forget hours.
Just get a very good survey w compression check by a locally well known surveyor w a good rep. Engine condition is the bottom line and what really matters. And lots of bad stuff happens to low time engines.

Back to the OP’s question. I don’t think there is enough data in the world to answer the question of how many hours are too many. Years appears to be a better indicator than hours but even that is full of exceptions. When I look at the boneyard, I don’t see boats with crazy high hours. I see abused engines or obsolete engines(cheaper to replace than to repair).

Would I walk away from a 10,000 hour engine? No, but I’m going to assume a rebuild is in the near future but then I might get lucky.

AS A simple rule of thumb 3 cubic inches per hp will keep one out of troubble.

Sure HD industrial engines can be worked harder , but boats seem to get farm tractor engine , bulldozer engines , light truck and taxi cab engines .

On the DD 6-71 the rule was between 20hp (forever) and 30hp (almost forever) per cylinder works with Natural engines.

I would be very wary of a older boat with low hours. Engines that have not been routinely (monthly) run and brought up to temp will have more problems than a higher hour motor that has been run and maintained.

The power vs displacement limit before durability drops off varies significantly between engine designs. For example, the current iteration of the Cummins B series seems to last quite well into the 400+ hp range if operated reasonably and not abused. But the slightly larger displacement Detroit 6-71 will have lost most of its lifespan if pushed to that same power level.

Generally, staying away from the highest ratings of a given engine model will significantly help lifespan. And as you narrow your choices down, do some research on the specific engine models in question (at the power ratings in question) to get an idea of typical durability, any specific concerns to look for, etc.

Compression tests, oil analysis, etc. can all help determine if an engine is healthy, showing significant wear, or has a potential major issue. As others have pointed out, maintenance and how the engines were operated make a huge difference. Think about the gas engines you're familiar with. There are big block Chevies out there in boats with 2000+ hours still healthy and running nicely. And plenty of other people blow them up well before 1000 hours.

Lengthy discussion on a 12kw Northern Lights Generator. Has 6700 hours on it - owner feels the slight mainseal engine weep should not have shown up until 10,000 hours, with some reportedly going 15k-30k hours between major rebuilds.

Ski in NC said:

Oil samples are a useful, yet imperfect tool. I have reviewed hundreds of marine diesel oil analyses. Their value really varies with the type of engines. I have seen Detroit two strokes that had absolutely worn out liners and rings, yet perfect oil samples. I have seen Cummins with flagged (by the lab) high wear metal numbers, yet checked out perfectly and went on for several years of good service.

I tend to focus on Na and K (salt or coolant getting in oil), soot content (oil not changed enough), viscosity, fuel dilution, flags for glycol or water. The wear metals (Fe, Al, Cu, Pb, Tn, etc) get some attention, but these can be really skewed by lots of sitting time.

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Ski, you know a lot more about this subject than I do, but my feelings exactly. I had them done on our previous boat, and now this one. Their primary use is to establish a baseline, and then looking for trends over years of usage. I have mine pulled every 2 years. I just reviewed my sample results this am and one came back as yellow "abnormal" for the Trans fluid due to lead. But, the lead amounts in the sample the prior 18 months were higher, but rated as green "good". I called the testing company and turns out the sample was miscoded as far as the Trans type and everything is fine - green.

I have two 2002 Cat 3406e rated at 800hp each with 5400 hours.

These Cats have been very well maintained and upgraded per Cat recommendations. Their care is not cheap but they run extremely well and have an expected life cycle of 15,000 to 20,000 hours.

I had a Cat engine specialist do extensive computer diagnostics on these engines, including interpreted oil sampling results and detailed physical inspection of parts and components. This was part of an all day sea trial survey. Not cheap, but bad engines would have been a deal breaker.

boatpoker said:

Photo below - 1971 Perkins HT6-354 - 20,000hrs when I rebuilt it. It didn't really need a rebuild, I just had nothing to do one winter.

A 3208 natural at 220hp with 3500hrs is barely broken in. A 3208 turbo boosted to 425hp may well be in it's last stretch at 3,500hrs.

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I owned a 3208NA in my freezer salmon troller that I had rebuilt at 20,000 plus hours. She needed the rebuild as the crank shaft bearings were just starting to show through the brass.

At the time I had the unit rebuilt the company owner who's people did the re-build told me to track the fuel consumed not the hours ran to define re-build time. He said that at 30,000 US gallons a well cared for 3208 is usually needing the re-build. These were Caterpillar certified mechanics specializing in Cats.

So, as noted, as horsepower increases along with speed and fuel consumption, engine life is reduced sooner.

I suspect most diesel engines may not be the same but are similar?

Engine Hours and Condition.

Oil analysis is a good idea, but how do you know how many hours the oil has on it? It seems like it would be best done if the oil is not absolutely new and clean! Regardless of hours, does the engine start after a few revolutions? Like touch the button and she fires up? Another hint: watch the engine when you shut it down. Upon shutdown, just when she kicks over her last couple revs, the engine should stop quickly and jiggle a bit in her mounts, like shudder a bit. In a diesel that indicates good compression. If the engine continues to try to run with the shut-off button pressed, dies slowly, it is a bad sign -- low compression, running on fumes sucked up form the crankcase. General condition of the boat tells you a lot. Even if it has had multiple owners, a clean engine room without leaking accessories, a lot of oil smell, and soot and grime hanging from the overhead beams is good sign. Happy Hunting!