Engine TBO

In buying a used trawler type vessel, what would be the maximum operating hours or years in service of the Diesel engine beyond which an overhaul would be considered necessary for reliable service? I know that you can perform SOAP samples and cylinder compression tests as a aid in diagnostic analysis but these will not necessarily show the degree of corrosion on the internal components. As these marine diesels are very expensive to overhaul, a low time, thirty year old set of engines might not be such a good bargain.
With aircraft engines, I look very carefully at an engine with more than 10 years of service. Aircraft with more than 20 years since a new or overhauled engine, I consider “runout” no matter what the number of hours are.
I understand that aircraft and marine diesel engines are very dissimilar power plants but the marine environment is a tough act. Many of these power plants are pushing 40 years without being opened up for inspection. Commercial vessels often go 30K-60K hours between overhaul, but they are run hundreds if not thousands of hours a year. A 1985 trawler with 3500 hours has been run an average of less than 100 hours per year. Sitting idle for extended periods without the manufactures preservation instructions having been accomplished is never good for any engine.

The hours makes no difference If it has had proper maintenance and regular oil and filter changes it will last many many years but if it is neglected it wont last long at all

I agree.

"proper maintenance and regular oil and filter changes"

So when first looking at a boat take a look and see what the owner has on the shelf.

Car oil or diesel rated ?, car antifreeze or diesel with SCA if needed?.

A bit of eyeballing will tell a lot about the maint.

Someone that keeps an engine maint log might be a better investment that a "what me worry" owner.

Airplane engine life is an entirely different situation than marine engine life. Airplane engines operate in a narrow power band and by law undergo annual inspections. Also no operator in his right mind would skimp on maintenance.

There is a wide variety of good, bad and ugly maintenance and operation of marine engines which makes engine life impossible to predict. If you maintain it by the book (and then some) prop it and operate it reasonably then it can last 10,000+ hours or enough that the vast majority of recreational owners will never see the end.

David

For buying an older engine, I think I would check blow by, and otherwise just check for smoke and all the usual stuff. Then go cruising.

In my completely unscientific observation, marine diesel engines that require rebuilding are 99% of the time a result of abuse of high output engines or sea water intrusion because of crappy exhaust designs. And 1% of the time because the engine actually failed or wore out.

I do engine surveys (or call it assessments, inspections, whatever) and the above posts have it about right. Run time hours have little bearing on engine condition, well until you get up in to the super high hours. 3500hrs is no where near that. What takes these engines out is corrosion both inside and out, running outside of the desired operating envelope, and sudden catastrophic death from things such as overheats or loss of lube.

Wear from hours almost a non issue, unless you are talking about a boat that runs on plane for a big part of the duty cycle (sportfish, fast cruisers, etc).

The condition of the engine can be assessed to about an 80% level of confidence regarding its condition. Real hard to get that last 20% without tearing it down and inspecting each part, but that is simply not practical.

Since the consequences of an engine failure on a boat are no where near as severe as on an aircraft, it is usually ok to roll with knowing 80%.

Different brands and models of engines have different weak spots so no way to tell what to look at except in the most generic terms.

Post what model engines you are looking at. Most likely someone here owns the same and can tell you what to look for.

djmarchand said:

Airplane engine life is an entirely different situation than marine engine life. Airplane engines operate in a narrow power band and by law undergo annual inspections. Also no operator in his right mind would skimp on maintenance.

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General Aviation aircraft suffer from the same condition as many privately owned boat, the owners can buy them but they can't afford the maintenance. You would be shocked to see the condition many of these airplanes are in with owners continuing to fly them.

And you see the same thing at marinas, boat after boat that hardly ever sees and preventative or routine maintenance.

"sea water intrusion because of crappy exhaust designs."

No question , but how many folks carry 3 oil changes aboard so the engine can be flushed and operated after the problem is repaired?

Mostly only ex long distance sailors.

I've always wondered why engine run hours is used as the basis for maintenance (oil change every XXX hours) or remaining life. Wouldn't 100 hours at 3600 RPM be a lot more wear than 100 hours at 1800 RPM?

aboatman said:

I've always wondered why engine run hours is used as the basis for maintenance (oil change every XXX hours) or remaining life. Wouldn't 100 hours at 3600 RPM be a lot more wear than 100 hours at 1800 RPM?

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Yes, definitely. Manufacturer's recommended oil change intervals are just an approximation that fits everyone. When I cruised a twin catamaran long distance with 36 hp Yanmars, I didn't think twice about extending the oil change interval to 200 hours rather than the manufacturer's recommended 100 since I was running moderately loaded and put a lot of hours on it every month. I did run an oil analysis once at the end of 200 hours and fuel and soot were fine.

In fact on our new Mini Cooper the engine's ECU integrates load over time and tells you when to service the engine, supposedly between 10,000 and 15,000 miles or every 12 months. I think you will see more of this on automobiles and maybe electronic marine diesels. The data is there to figure it. You just need to get customers used to this plan. The operating manual didn't say anything about the 12 mo limit, so I had to call the dealer to figure it out when the message came on at 12 months even though the miles were less than 10,000.

David

aboatman said:

I've always wondered why engine run hours is used as the basis for maintenance (oil change every XXX hours) or remaining life. Wouldn't 100 hours at 3600 RPM be a lot more wear than 100 hours at 1800 RPM?

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Actually what the manufacturers would prefer to use is fuel burn. However, long ago hour meters were installed, not floscans, and so hours became an approximation. i'm not convinced fuel burn would be better.

djmarchand said:

In fact on our new Mini Cooper the engine's ECU integrates load over time and tells you when to service the engine, supposedly between 10,000 and 15,000 miles or every 12 months. I think you will see more of this on automobiles and maybe electronic marine diesels. The data is there to figure it. You just need to get customers used to this plan. The operating manual didn't say anything about the 12 mo limit, so I had to call the dealer to figure it out when the message came on at 12 months even though the miles were less than 10,000.

David

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My 2011 truck (diesel) does the same thing. It tells you what % "consumed" your oil and fuel filters are. I don't know exactly how it's calculated, but it might be fuel burn. Unlike days gone by, the ECU in a fuel injected engine knows exactly how much fuel has been burned, so that would be an easy way to do it.

I found an article by Caterpillar that recommended engine overhaul at 30,000 gallons of fuel consumed. This was for a 3208 engine in a motorhome chassis. They seem to be the most concerned with the rod bearings as the recommendation was to replace these bearings at 25,000 gallons. I would imagine that the motorhome installation would present a similar operating load history as the installation in a trawler.
30,000 / 4.5 GPH = 6,666 hours. No mention of time in service, only fuel consumed. If you ran it hard, like a DeFever 53 POC on plane, you could realistically average 10 GPH? 30,000 / 10 GPH = 3,000 hours.

Measuring engine life by gallons consumed is by far the most accurate method.