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Old 08-16-2012, 08:02 PM   #61
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This is a long thread so maybe this concept has already been proposed. I've seen it suggested (and tend to support) that the life of any engine is related more to the amount of fuel run through it than it is to hours of service. So you can run a lot of fuel in a short space of time or a lot of fuel over a longer period of time but either way when you hit the total fuel consumption your time is up.
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Old 08-16-2012, 08:17 PM   #62
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Originally Posted by bobofthenorth View Post
This is a long thread so maybe this concept has already been proposed. I've seen it suggested (and tend to support) that the life of any engine is related more to the amount of fuel run through it than it is to hours of service. So you can run a lot of fuel in a short space of time or a lot of fuel over a longer period of time but either way when you hit the total fuel consumption your time is up.
I have heard the same from Cat Engines.....
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Old 08-16-2012, 08:24 PM   #63
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This is a long thread so maybe this concept has already been proposed. I've seen it suggested (and tend to support) that the life of any engine is related more to the amount of fuel run through it than it is to hours of service. So you can run a lot of fuel in a short space of time or a lot of fuel over a longer period of time but either way when you hit the total fuel consumption your time is up.
I would think wear (and engine life) would be more related to the total number of revolutions and have often wondered why modern engines don't count the number of revolutions to determine routine maintenance schedules rather than engine hours (which could be at 1K RPM or 4K RPM). Cars and trucks would have an even greater range.
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Old 08-16-2012, 09:56 PM   #64
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Fishermen are like old ladies when it comes to spreading bad news or rumors. If the Lehman 120 was a subpar engine they would have been ripping them out right and left many years ago. As a broken down boat is lost time and lost money. One of my old boats, built in 1965, wood, dry exhaust, stern picker, is still fishing out of Blaine, Wa. Boats name is "Summer Sun." Still running the same engine, no idea how many hours (no meter), they did a valve job on her this Spring and they fish both crab and salmon. That's nearly 50 years of use! How much more service life can you expect??

Unfortunately, many opinions and rumors become "truths" in peoples minds over time. I'm sure there was at least some grain of fact to this discussion at one point. But I agree with the previous post that no one is likely to change their mind or opinion based on what was discussed here.

I just hope someone doesn't walk away from here thinking Lehman's are weak, have to be babied, or doomed to fail engines. That's just not the case. They're in thousands of boats and one of the more dependable power plants that I have experienced. Don't be afraid to run them as they were intended.
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Old 08-16-2012, 10:08 PM   #65
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I would think wear (and engine life) would be more related to the total number of revolutions and have often wondered why modern engines don't count the number of revolutions to determine routine maintenance schedules rather than engine hours (which could be at 1K RPM or 4K RPM). Cars and trucks would have an even greater range.
Mostly because the wear is more related to load than simply number of revolutions.

An engine that is overloaded may operate a low number of revolutions for a given period but the stress is very high and results in damage that might show up immediately or later. A moderately loaded engine can do the same number of revolutions with no problems.

A generator or compressor engine might rack up a jillion revolutions but never see anything but light loads and run for years while a rock crusher engine might go from no load to overload and back again within minutes or every few thousand revolutions and break something pretty quick.
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Old 08-16-2012, 10:34 PM   #66
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Originally Posted by bobofthenorth View Post
This is a long thread so maybe this concept has already been proposed. I've seen it suggested (and tend to support) that the life of any engine is related more to the amount of fuel run through it than it is to hours of service. So you can run a lot of fuel in a short space of time or a lot of fuel over a longer period of time but either way when you hit the total fuel consumption your time is up.
This reminds me that I have heard we have a finite number of heart beats and once you hit your limit, you are done. Of course, I have only heard this from people using it as an excuse not to exercise and get their heart rate up.
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Old 08-16-2012, 10:34 PM   #67
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Don't be afraid to run them as they were intended.
Larry B.
We do. We run them as though it was the 1950s when the POS was designed.
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Old 08-16-2012, 10:57 PM   #68
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Marin,
The engine manufacturers rate these engines to run continuously at near full load and near full rpm and they are said to last 10 to 15000 hrs. If you run your engines at 75% load for 10000hrs or if you were to putsy around for 10 to 15000hrs you'd prolly be 147 years old by the time you achieved the engine time and usage and either engine would still be in good shape given the maintenance I think you do. Maybe you could run most engines at WOT for 10000hrs? Our boat engines just don't wear out. They get killed instead.
Did you know it would take $240,000. to run a Lehman 10,000hrs at WOT?
And it would take 20 years at 500hrs a year to do 10Khrs.
You're going to need lots of time and money. But if you're right Marin maybe you'll need something like a couple million $ for fuel and 40 to 50 years.
I don't see much difference myself. But then I'm old.
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Old 08-16-2012, 11:18 PM   #69
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The engine manufacturers rate these engines to run continuously at near full load and near full rpm and they are said to last 10 to 15000 hrs.
Maybe today's engines, I don't know. But not the FL120. The reputation of going 12,000 to 14,000 hours in recreational boat service is based on them running in their "normal" rpm band of 1500 to 1800 rpm. So say the people with the most experience with these engines in marine service, anyway.

I'm sure you're right about the fact I'll never see the maximum life of our engines whatever it may be. But how I operate engines is a matter of principle with me.

What I have seen is the results of two different cruise power settings in an aircraft engine. These are engines that at the time had to be overhauled every 1200 hours. The engines that had been run in cruise at 19" of manifold pressure had noticeably more wear on some components than the identical engine that had been run for the same number of hours at 17" of manifold pressure. This was a pattern, not a one-time observation.

I know aircraft engines and truck diesels are two different things. But making metal work harder yields the same results no matter what, I think.
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Old 08-17-2012, 06:42 AM   #70
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"The engine manufacturers rate these engines to run continuously at near full load and near full rpm and they are said to last 10 to 15000 hrs."

SOME engine mfg.

IF you are able to find a graph from the Mfg of the ratings , and time allowed at the different allowed power levels GREAT.

HOWEVER

Just an advertising claim of XXX hp at YYY rpm does not mean the engine can be run there 24/7 , or even for a half hour.
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Old 08-17-2012, 08:51 AM   #71
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Mostly because the wear is more related to load than simply number of revolutions.

An engine that is overloaded may operate a low number of revolutions for a given period but the stress is very high and results in damage that might show up immediately or later. A moderately loaded engine can do the same number of revolutions with no problems.

A generator or compressor engine might rack up a jillion revolutions but never see anything but light loads and run for years while a rock crusher engine might go from no load to overload and back again within minutes or every few thousand revolutions and break something pretty quick.
But the common "every X hours" schedule is no more accurate.
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Old 08-17-2012, 09:00 AM   #72
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...............Unfortunately, many opinions and rumors become "truths" in peoples minds over time..........
Yes indeed. And web forums perpetuate these supposed "truths", especially when the more prolific or dominate posters post them every chance they get.

Whatever the subject, be it a marine engine to a TV dinner, there are those who think it's the best thing since sliced bread and those who think it's a pile of garbage.

In the end, they are nothing but opinions and pretty much only the people who don't like a product will bother to post his or her opinion. The satisfied users are just happily using the product and thinking about other things.
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Old 08-17-2012, 09:08 AM   #73
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But the common "every X hours" schedule is no more accurate.
You have to start somewhere and then go "on condition." The manufacturer just makes its best guess and lets the real world determine the accuracy of that guess.

That aircraft engine Marin wrote about that required overhaul at 1200 hours ... that was a requirement for use in commercial service, it is only a recommendation for private use. Regulators are allowing longer times between overhauls, sometimes by incremental increases in hours and more often based "on condition" because some operators in some situations can obtain far longer service life than others in different situations.
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Old 08-17-2012, 01:01 PM   #74
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Yes, you can use an "extended TBO" program and by submitting oil analyses periodiclally and keeping certain kinds of records and meeting other requirements you can extend the TBO of an engine, even in commercial service, for quite awhile as long as the engine's condition falls within the paramenters. And, in the case of the commercial operator I am very familiar with, running the engines more conservatively helps them get a much longer TBO with this program.
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Old 08-17-2012, 01:10 PM   #75
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So what about the idea of running WOT for a few minuts every so often to blow out the carbon build up.

Good idea or bad?

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Old 08-17-2012, 01:18 PM   #76
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We don't do it for the reasons I've described, and we've been advised not to do it by people who know far more about the FL120 than anyone on this forum. So that's good enough for me.

As far as other engine makes and models are concerned, I have no idea if it's good, bad, or indifferent for them. We wouldn't do it with any other type of engine simply because I don't believe it really proves anything and why run something hard when you don't have to? But others have their own opinions and beliefs and so follow whatever practices they wish: the only engines we care about are ours.

I do know that Carey, who these days runs his 420 hp Cat at fairly low rpm for a boat speed of about 9 knots (the boat's normal cruise speed is about 15 knots) periodically runs the boat at its 15 knot rpm for awhile. It's my understanding that this is more for the benefit of the turbocharger than the core engine itself.
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Old 08-17-2012, 02:08 PM   #77
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Thumbs down Underloaded engine

Most of this discussion has been about why loading increases wear, but there hasn't been a lot of discussion on why you should push the engine a bit.

Diesel engine exhaust temperature is a function of load. In a lightly loaded engine, the exhaust temperatures are low and you run the risk of wet stacking, which is where you get incomplete combustion. This can cause carbon to build up on the injectors and valves, which can cause even less efficient fuel burn, leading to more unburnt fuel.

Here's some data from my boat. This is for the new John Deere engine which replaced the 5000 hour Lehman 120. For reasons no one has yet to explain, three center cylinders were scored. However, I don't think the PO ever pushed the boat above 1650 RPM, until I sea trialed it.

The temperature data below is post-turbo, so the EGT is probably 400-500 degrees hotter at the turbo inlet.

Note that at 1800 RPM, my 34' trawler is just above displacement speed.

RPM LOAD EGT
1600 29% 274
1800 34% 425
2000 45% 510
2100 50% 534
2200 60% 568
2640 99% 680 WOT

Now that the engine is broken in, I'll cruise between 1700 and 1800 rpm. I also run the engine at 2100 to 2200 for at least 10% of every trip.

Marin, given a slightly larger boat with twins, I would guess your engines are probably operating at 25% load. Have you had any problems with injectors sooting up?
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Old 08-17-2012, 02:20 PM   #78
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I have no idea if it's good, bad, or indifferent ... It's my understanding that this is more for the benefit of the turbocharger than the core engine itself.

Post #33: "Probably can't hurt much, probably doesn't do much other than burn off the oil and stuff that condenses in the cold exhaust manifold."

If it blows the oil and crud off the turbine wheel it is a good thing. It doesn't take much to create an imbalance that will lead to reduced turbo life.

Then again, there is an operating regime on a turbo where loading doesn't produce enough boost to provide adequate valve cooling. That is normally the result of compressor wheel fouling or damage but turbine wheel fouling can create the same issue. So, there is something else to think about, maybe long term operation at moderate loads can lead to overheating of exhaust valves ... we had that exact condition on a larger engine once and it stumped all of us until the engine manufacturer's engineer evaluated a lot of air flow and temperature data that showed our valve failures were the fault of the turbo and not a material failure. We replaced the turbo and haven't had a problem since.
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Old 08-17-2012, 02:43 PM   #79
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Marin, given a slightly larger boat with twins, I would guess your engines are probably operating at 25% load. Have you had any problems with injectors sooting up?
We have had the boat for fourteen years. While we use it year round, my work and other interests pretty much confine us to weekend or three-day trips except for one longer cruise a year. So the boat gets used a fair amount but not for a lot of hours. Most of our weekend trips are three to four hours out and the same amount back.

The engines do not run any differently today than they did fourteen years ago. There is a bit of blue smoke at startup, there is the typical sheen of unburned fuel out the exhaust whent the engines are cold, and that's it. They start as soon as the starter starts to turn them, they run smoothly throughout the rpm band we use, which is idle through an occasional 1800 rpm but mostly 1650. The one time we took them to WOT they did so without protest. The engine temps (coolant temps) are where they are suppose to be at 1650 rpm. We have EGTs and they are marked for the normal temperature at cruise and that's where they continue to indicate at cruise (about 600 degrees IIRC). We have never had to clean soot off the transom, swimstep, or swimstep-mounted dinghy.

The engines use no more oil today than they did fourteen years ago, which is less than one quart per engine every 100-150 hours which is our oil change interval.

All this isn't to say they both won't explode next week but so far the engines have not changed at all.
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Old 08-17-2012, 03:24 PM   #80
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Egt

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We have had the boat for fourteen years. While we use it year round, my We have EGTs and they are marked for the normal temperature at cruise and that's where they continue to indicate at cruise (about 600 degrees IIRC).
Marin, your EGT's are probably a good indication of engine load. I have know idea of what a good temperature would be for the LH120. My JD is turbo'd, so it's not a good comparison.

Any other Lehman's out there with EGT's? If so, it would be interesting to know what you're running.
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