Wide Open Throttle

[psneeld]

Good and bad on both sides. Hard to know who to trust sometimes.

--------------------------------------------------------

That is exactly my point. . . [/QUOTE]

But you made it sound like blindly following manufacturers recommendations was where it was at.

 

[markpierce]

Ran my JD at 1800 RPM for several hours recently, and near the end of the run, opened the throttle wide momentarily to reach maximum-governor-regulated RPM of 2400 (engine rated for maximum of 2500). This time the engine had a hard time reaching 2400 and the engine "bounced" between 2200 and 2300. Felt like a fuel-supply problem, solved by switching between the two Racors. Time to change that filter!

 

[RickB]

Yes but several other engine manufacturers say the same ...

Your thoughts on the pros/cons????

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.

Marin might be a bit overly conservative in his approach but it works for him and it avoids the condition where a problem is most likely to occur, during acceleration or deceleration. An engine is less prone to mechanical damage if it operates in a steady state condition, steady speed, steady load, steady temperature. It is when the hardware is stressed by acceleration, temperature changes, and increasing or decreasing load that a failure is most likely to occur.

Marin's description of his mentor's advice is sound, it falls under the "local knowledge" umbrella. Sometime the user base learns things about an engine that the manufacturer didn't or couldn't predict. If the user base is large enough and old enough the users figure out what to do and what not to do.

Marin's often mentioned P&W 985 is a great example, there have been many improvements to that engine based on user experience and it serves them well. The users and caregivers of those engines may be a bit more technically sophisticated than many recreational boat drivers but that doesn't mean that the collective experience of Lehman (or other engine) owners and users is not worth considering.

 

[FF]

Full throttle no load should probably be checked (15 seconds) each year on comissioning.
With a warmed up engine. It is a problem finding tool.

Running on the pin underway should cause no hassles for 10min every so often also as a check ,10 min will find any problem.

A realistic high cruise is down 10% (in RPM) or usually 300 rpm down from the RPM found on the full throttle in gear.

EG engine 2700rpm no load, 2500 full tilt underway , 2200 rpm is your get home , damn the fuel burn or wake speed.

"High Idle" is a special condition used on coaches and some machinery to operate heavy loads like an air cond unit .

I have never heard the term used to describe the no load gov setting.

FF

 

[Moonstruck]

"High Idle" is a special condition used on coaches and some machinery to operate heavy loads like an air cond unit .

I have never heard the term used to describe the no load gov setting.

FF

It's in my Cat manual.

 

[jleonard]

It is also called high idle by Cummins.

 

[Marin]

Marin might be a bit overly conservative in his approach but it works for him and it avoids the condition where a problem is most likely to occur, during acceleration or deceleration.

I'm sure I do take a more conservative than "normal" approach to operating engines. But fixing them is expensive, or if I do it myself a time-consuming pain in the ass, and replacing them is even more expensive. So my objective in operating an engine--- any engine--- is to maximize its service life and the time between when something has to be fixed or replaced.

That's not to say I don't use them as they are designed to be used. I use the full rated manifold pressure in the radial when I take off, I drive my car at 70 or 80 mph when I can. But I don't ask more of an engine than I actually need to accomplish something.

I consider myself very fortunate that I have been in aviation and boating at the tail end of what I consider to be their "golden ages" in terms of the people in it. Guys like Bob Munro who started Kenmore Air Harbor and did more with floatplanes--- both flying and fixing them--- than most other men in the same business. On the boating side, it's been people like Bob Lowe who founded the Grand Banks owners forum and who made a successful career as a shipwright and boatyard owner fixing, restoring, upgrading, and maintaining boats like Grand Banks, wood and glass. And our acquaintance in the UK who became an absolute master at diagnosing, fixing, and overhauling diesel engines.

These were people who did what they did through common sense, an inherent ability, self-reliance, and who worked at at time when one was required to do a lot on their own. Bob Munro was a brilliant seaplane pilot, but he was also a brilliant powerplant mechanic. Whatever happened to his plane during a flight he could fix when he got back. Or on the spot if necessary. As opposed to people today who are forced down a limiting path by countless regulations and requirements and with whom the attitude is often "it's someone else's problem." I have learned to have a tremendous respect for these "old guys" because today, when they say something having to do with their field of expertise, they are almost always right even if it flies in the face of the armchair theorists.

This WOT topic comes up from time to time on the Grand Banks Owners forum. Bob Lowe had a response fairly recently that has stuck with me so I went back and found it. Here is what he had to say in response to a member who advocated taking the engine in his GB to WOT for five minutes every time the boat was run. ---------

"The purpose of the WOT runs is to stress test the engine components for weakness. Same as when you go to the doctor and he puts you on the treadmill and stresses your heart. Of course, some people have a heart attack while doing the stress test.

"My personal opinion is that I do not want my boat to have a heart attack when I am out cruising so I make sure to properly maintain those components that can fail, such as raw water pumps, water pump, fuel pump, and so on and make sure to change oil and filters as needed and maintain the cooling system, hoses and belts to keep the engines in top condition. I believe that is the best insurance against premature failure.

"The added wear and tear of the WOT runs may give one confidence that the engine is in good condition, but is it worth it if it also stresses the engine components to near failure and results in premature failure?

"Just as I don't go to a doctor for stress tests on my heart to satisfy his curiosity, I don't do stress tests on my engines to see if they will fail. Instead, I try to keep all components in top condition and I also carry plenty of spares to fix any but the most severe failures."

 

[RickB]

Bob Lowe had a response ...
"The purpose of the WOT runs is to stress test the engine components for weakness."

I don't necessarily agreee with that. If the manufacturer rated the engine to produce 99 horsepower continuously, then it is designed to be run that way 24/7 until it wears out. If it is rated at 110 for 1 hour out of 24 and 99 for the other 23 then it can be used that way.

If WOT delivers the rated ouput or less and is within the specs there is no valid reason to self-impose some other restriction based on docktalk. There may be real world conditions such as Marin mentioned with the Minimec fuel pump but that one seems to be related to frequent speed and load changes, not continuous operation.

The question was "For how long and how often should you operate the engine at WOT?" The answer is as long as the manufacturer says you can run it at that power or until you get tired of buying fuel. Operating at rated output is not conducting a "stress test." That has already been done in the manufacturer's test cell so he could develop the charts you need.

 

[Marin]

You're correct, but..... The issue, at least for me, is not will an engine run continuously at WOT but for how long? Absolutely, it can run at rated power 24/7 until it wears out but in the case of a powerplant like an FL120, that "wearing out" is going to occur pretty soon if it's run that way. As opposed to going 12,000 to 14,000 hours in recreational boat service given proper operation, servicing, and maintenance, which is the reputation that particular engine has when it's run in the 1500-1800 rpm range.

Engine manufacturers all provide the maximum rated power of the engine, but I've only ever had two owners manuals say that "this engine is rated at x hp continuously for y period of time."

The radial in the airplane I fly is rated for full power (450 hp) for exactly one minute. If you don't back the power down to METO (Maximum Except Takeoff) or less at that one minute mark, all bets are off as to the longevity of the engine. In the Cessna 206 I used to fly, its Continental IO-520 was rated at 300 hp for five minutes at which point the power had to be backed off. In both cases these limitations are spelled out prominently in the operators manuals.

But there is nothing in our FL120 manual that says how long the engine can be run at maximum power. So it's a crap shoot if you choose to operate that way. You can do it, but I suspect you will soon be on the phone to Bob and Brian Smith at American Diesel.

As to newer engines, I'm sure they can do it, too, for at least as long as the warranty is in force.

 

[skipperdude]

A friend of mine is a mechanic. For Chrysler.

the engine computer has an ap that records the ammount of time a diesel truck is used as it is intended.

There is seldom greater than 2% of the time a diesel pickup actually is under load.

SD

 

[skipperdude]

Aren't airplane engines Gas.

World of difference between the two.

The governor will not let the engine run any faster than it can before damaging the engine.

That is the maximum governed throttle rating.

Most surveys need to operate at wot to determine if the boat is propped correctly or if some other issues are at play such as excess exhaust back pressure.

It should even tell you if the bottom is clean and how much extra weight you are carrying.

I have heard that somewhere between 3 to 4 hundred RPM"s within rated RPM.

One of the reasons that to increase RPM you reduce pitch on the prop.

You can't tell these things without running at WOT.

SD

 

[Marin]

You can't tell these things without running at WOT.

SD

We ran at WOT for a few minutes to get the data our prop shop needed. So I'm not saying never do it. I'm saying that I believe there is no point in shortening the life of the engine by doing it unnecessarily. If our FL120 manual said "You can absolutely run this engine at 2500 rpm continuously for 14,000 hours" we'd do it. As I've said before, slow sucks, and running our engines at 2500 rpm gets us some 11 knots or a bit more.

But I don't see anything that says that in our FL120 manual.

What I do have is people with direct experience with this engine in all sorts of uses telling me what a failure this engine is when run hard and fast.

So I've got a theoretical, unknown longevity running at WOT on one hand and a very well known poor record of longevity at high power settings on the other hand. Guess which one I'm going to base my engine operation on?

 

[skipperdude]

I'm with you all the way On this.
You have a unique situation as indicated by information gleaned from reliable sources.

I am not saying you or anyone else should run at WOT.

Just saying it is a diagnostic tool that should not damage the engine.

And a lot of information can be learned by operating at WOT occasionally.

You just should not be afraid to do so. There are benefits

SD

 

[RickB]

But there is nothing in our FL120 manual that says how long the engine can be run at maximum power.

Ah, you must not have the right manual. According to the Lehman manual 4C61J dated June 1986, the normally aspirated 6 cylinder engine is rated at the old and outdated BS Overload rating of 120HP@2500 rpm. The continuous rating under B DIN 6270 conditions is 114.5 hp at 2500 rpm.

So, the bottom line is that engine can be operated 24/7 at 2500 rpm as long as the power extracted doesn't exceed 114.5hp.

You can choose to use less but that is a self-imposed limitation and may or may not extend the operational life measured as power produced over the engine's life. I suspect that if you operated it at constant speed and load at full continuous power it would last just as long as it would the way you are using it.

I used to run a trio of those engines driving pumps on a fuel barge where they ran at full WOT for an average of 14 hours a day for several years that I was around it without requiring much work other than routine maintenance.

 

[Tom.B]

I run mine up to WOT (under load) a couple of times each season. I usually keep it there for (about) 2 minutes or so. I watch for exhaust smoke, steam, and monitor coolant temp.

I do this for about 5 minutes returning from trips over a few hours.

 

[Marin]

So, the bottom line is that engine can be operated 24/7 at 2500 rpm as long as the power extracted doesn't exceed 114.5hp.

Our manual has similar wording. But nowhere does it define how long the engine will run in hours at its continuous rating. 1,000 hours? 5,000 hours? 10,000 hours? More?

Considering everything will be running at near its maximum temperatures and pressures, is the manual saying my engine will run forever at that rpm and load? Will it run 20,000 hours? Are they saying there is no more wear and stress on the engine components at 2500 rpm as there is at 1500 rpm? Or 1650 rpm which is where we choose to operate them?

If there is no value in running an engine at anything less than maximum continuous rpm (other than fuel burn, and in the 1950s when this engine came out fuel cost was not an issue) then why isn't everyone running the engines in their boats at maximum continuous rpm all day, every day? Because the theory seems to be saying that in the case of the FL120, we'll get the same 14,000 hour life out of the engines running at a continuous 2500 rpm at maximum load as we will at 1500 rpm.

Reality doesn't seem to bear that out and reality is the only thing I'm interested in.

 

[Nomad Willy]

Rick,
I had a 120 Sabre (same Ford eng as the Lehman) and I seem to recall the 114hp continuous load rating.
I like to prop to rated speed at WOT but to insure I can't overload the engine I prefer being 25 to 40 rpm under propped. But one inch of pitch change changes the rpm on my boat 200rpm so one cal only come close unless you're willing to carve away a little blade area to change 50 to 100rpm.
Re the fuel pump problem Marin spoke of it seems to me that if there was something wrong w the design or parts used people would have fixed the problem long ago. Marin have you ever asked a marine propulsion engineer about this Lehman weakness?

 

[RickB]

Our manual has similar wording. But nowhere does it define how long the engine will run in hours at its continuous rating. 1,000 hours? 5,000 hours? 10,000 hours? More?

Do you seriously expect it to?

Considering everything will be running at near its maximum temperatures and pressures, is the manual saying my engine will run forever at that rpm and load?

They are simply saying you can run it at that speed and load until it won't run anymore. When that is depends on things they can't control and aren't foolish enough to define.

If you ran it at constant speed and load, it might well run "forever" ... they do in some applications.

If there is no value in running an engine at anything less than maximum continuous rpm (other than fuel burn, and in the 1950s when this engine came out fuel cost was not an issue) then why isn't everyone running the engines in their boats at maximum continuous rpm all day, every day?

Some people do in some applications. You choose not to, no one is saying you have to, just that you can if you want to. It's your engine, run it however you like. The point is that the engine is designed and rated to deliver a specified continuous output and the only reason not to take advantage of that output is personal, not technical.

If you run it at varying speeds and loads then you might not get as long a life out of certain components, as your acquaintance advised you. That doesn't mean running it at maximum rated power is going to wreck the engine or shorten its lifespan which is measured in horsepower hours or weight of fuel burned.

I doubt that many readers wake up in the middle of the night wishing others would run their engines differently. I know I don't.

 

[markpierce]

JD gives my 4045DFM70 an "M2" rating, but I'm not too sure how to apply it when choosing how to operate:

M2
Typical load factor≤ 65 %
Typical annual usage (hr)≤ 3000
Typical full-power operation (hr)16 of each 24

 

[Marin]

They are simply saying you can run it at that speed and load until it won't run anymore.

So it's basically a meaningless discussion because what I'm interested in is maximizing the service life of the engine. Speaking about the FL120, which is the only marinized diesel I have any experience with, there is a ton of evidence that this engine will go and has gone 12,000 to 14,000 hours in recreational boat service when operated in the 1500-1800 rpm band and zero evidence that I've ever seen or heard about that it will go any specific length of time at all when operated as a boat's propulsion engine continuoulsy at 2500 rpm. Yes, Ford of England said it would run this way until it fails. But "until it fails" doesn't tell me anything of any value in terms of maximizing the service life.

Which gets us back to the WOT test topic. As Bob Lowe said, "I don't do stress tests on my engines to see if they will fail." Because one never knows when Ford's "until" will occur. Even Ford had no idea apparently although they soon learned their design was not up to the task they designed it for.

How other people operate their engines is of no concern to me. And my comments and the reasons we do what we do with our engines apply only to the Ford Dorset engine (base engine for the FL120). That's the only engine about which I have researched its development and history and have talked to people in the engine business about. Whether any of what I learned applies to other engines, even other Ford engines marinized by Lehman like the Dover, I have no idea.

Understand, Rick, that I have no argument with the points you've been making about engines and their rated power. You have forgotten more about marine diesels than I could ever hope to know. My perspective on the matter is solely geared toward maximizing the service life of the engines in our boat. While I won't live to see it, my focus is on having these engines reach that 12,000-14,000 hour mark. Even if we re-engine the boat down the road here a bit, that does not change our desire to maximize the service life-- and thus minimize the problems---of the engines we have now.

Which is why we follow the advice and recommendations of people who have dealt with the Dorset "back in the day" and who know from direct experience what shortens its life and what keeps it going and going like the Energizer Bunny and his damn drum.

 

[Edelweiss]

Maybe there is some confusion here. My sense is that the "red line" of a gas engine and the "manufactures rated output" of a diesel (which is ideally within a couple hundred rpm of WOT) are assumed to be the same thing?? They really are two different measuring sticks for different engines and applications. Run an engine at "red Line" for extended periods and it will come apart sooner than later.

We owned four commercial gillnet fishing boat, three with the FL120 Lehman engines and one 6.354M Perkins. (Stove oil was only about .35 cents per gallon then and that is what we burned.) The boats were usually run near WOT to and from the fishing grounds, usually at least 2 hours each direction with 8 to 10 hours of idling in between and a few minutes of WOT every couple of hours while running the nets.

They were used boats when we bought them in 1970 and still running fine 10 - 12 years later when we sold them. We had starters and batteries fail, fuel filters plug, water pumps wear out, impellers fall apart, hydraulic pumps leak, belts and hoses wear out, etc, etc. but never an internal engine or injector pump failure. These engines were and still are rock solid. I would doubt that there are many applications which test the guts of an engine more than commercial fishing or a work boat.

If you want to run faster or a little slower, do so!! You're not hurting the engine. Choose the speed you are comfortable with and can afford to cruise at, but do it because that is what you want to do. Change the oil and filters as recommended and they will literally out live you.

IMHO
LB

 

[FF]

Most of the engines in our sized boats are marinizations of something.

Every truck will be at WOT for a while climbing hills , with no long term problem.

Yard impliments frequently run gov. WOT to power their PTO .

 

[Nomad Willy]

Very good discussion Rick, Edelweiss, Marin and FF,
It's not a "meaningless discussion" Marin though the meaning isn't clear to you. I understand why you say that though. And I don't think anyone will change their ways over this discussion but that dosn't make it meaningless. The meaning is in the path that we take uncovering all the stones that relate to the elements of the topic at hand. If everyone said running my engine above 2000rpm is bad for it I'd prolly still be running at 2300 but I'd know a lot of opinions and information both good and bad about the possible bad effects that could emerge. Marin is being a bit stubborn about this high load business but he HAS run at WOT for testing his engine and it's load and w the Lehman 1650rpm is probably fine. But I don't believe the Lehman is anywhere as weak as Marin says it is.
Another thought/concept I'd like to add to this WOT stuff is that a meaningful way to look at the correct way to run at WOT is that the engine needs to burn the fuel correctly that the engine is given to be propped right. If propped right the engine can burn any amount of fuel that it can be given. At high throttle settings the overpropped engine cannot.
But still running their engine at WOT for any reason under any conditions will still be so distasteful and scary that there will be many here that will never do it. Running an engine at very high speeds and loads that sounds like it's connecting rods are loose will be scary to those of us that are so very used to quiet gas engines. And we started that highly ingrained relationship when we were almost babies. But they now know a great deal about what can be learned by doing it and that one's engine MAY not come flying apart in many pieces and this is why this discussion is NOT meaningless Marin. The meaning is what's in our heads after the discussions and the experience we've had in the discussions. The love you have for your wife when she dies isn't nearly as important as the millions of experiences you've had w her over the years.

 

[RickB]

Considering everything will be running at near its maximum temperatures and pressures ...

The thing is those limits are imposed by the manufacturer as the top of what they allow for longest lifespan at the highest output power they describe as continuous.

They determined that the loads and stresses at max rated power, temperature, pressure, and rpm are OK to operate continuously for what they are comfortable will provide adequate engine life that will not trash ithe company reputation.

The "redline" does not mean the point where the thing detonates. It is a limit beyond which the manufacturer will not take responsibility for long life and happiness.

Self imposed operating limitations may or may not contribute any more to long life than operating at the limits may shorten the life. There is considerable anecdotal information to the contrary ... why do you think so many folks are scared to death to operate at low loads? Now we have people who are fearful of operating at rated loads ... the operating envelope seems to be getting smaller by the day.

As far as high idle is concerned, in practice there is little reason to run an engine that way for more than a few seconds, it proves nothing other than the governor is set correctly. An engine that runs at max rpm and no load is doing nothing other than converting fuel to noise and heat ... there are cheaper ways to do that then run a diesel.

 

[Marin]

But I don't believe the Lehman is anywhere as weak as Marin says it is.

Eric--- I think you missed the point a bit. I don't say the engine is weak because I have no way of knowing this not being an engine designer or manufacturer or repair shop owner. I'm simply repeating what people who are these things have told me, as well as what I have read about the Dorset engine's development and operational history.

The fact that Ford of England came within a hair of taking the engine out of production because it proved to be such a miserable failure as a truck engine should tell you something. In truck service, it overheated at the drop of a hat, blew head gaskets, warped its head, scored cylinder walls, and that was assuming the engine even got that far since its in-line injection pump was usually the first thing to fail.

Ford of England was ready to cease the manufacture of the Dorset engine altogether when someone--- don't know who--- used it in a stationary industrial application. IIRC it was in a crane but maybe not. Anyway, in this relatively low load, relatively constant rpm application it did great. The word spread, so to speak, and the engine became popular for running pumps, generators, hydraulic systems, and so on. It also proved very good in agricultural applications like tractors and, in particular, combines. In fact in the UK the Dorset engine is still referred to by some as the Ford Combine Engine.

Relatively low and constant load (compared to trucks) at constant rpm is the definition of a lower-power marine diesel, so it was inevitable that the Dorset attracted the attention of companies which created marinization kits for existing engines. Lehman is the most well-known today for its FL120 and they probably produced the most kits but they are just one of many companies, some large, some very small, all over the world which marinized the Dorset engine.

I've learned all this over the years from research I did in the UK not long after we bought our boat because I wanted to know more about its engines as well as talking to people with a lot of first-hand experience with these engines as I've related before. These aren't conclusions I've arrived at on my own based what I knew about the engine, which before all this was nothing.

Bottom line is these people's opinions are that the Ford of England Dorset diesel is a Not Great engine as engines go. Its design and manufacture and the components chosen--- like the injection pump--- rendered it an outright failure for its intended purpose. Only in service that did not greatly tax the strength and design of the engine and its components did it prove to be reliable. Very reliable, as it turned out, so it got a new lease on life at Ford.

The Ford Dorset is the only engine I have researched and discussed with people in the engine industry. So what I have related here and earlier applies only to that engine. I know virtually nothing about the Ford Dover engine which Lehman marinized into the FL135. The Dover came later than the Dorset although I believe the manufacture of both engines overlapped. The only thing I know specifically about the Dover is that its injection pump is lubricated by the engine itself, not from a self-contained sump like the pump on the Dorset engine.

The British have a tradition of naming their engines--- Merlin, Griffon, Trent, etc. Ford wasn't as creative in naming its engines--- the Dorset and Dover diesels were named for the plants in which they were manufactured.

 

[Nomad Willy]

Marin,
Most of the time when I don't accept what you say It' because of your sources. Many of then I believe to be not objective or just passing on stuff believing it because they heard it or they think it's what the other guy wants to hear. Old wife's tales get passed along in a place like this like very readily. Stuff like a heavier anchor is better than a light anchor. Not that there's no truth in that but there is much more to it. No thinking just "yeah man that's for sure".

But in this case it sounds like you've got so many sources that if most of the facts are true (and it sounds like it) then it may be indeed it's a crap engine. I know the Sabre wasn't and it used the engine lube oil in the HP injection pump. And for those that don't know the 120 Sabre engine uses the same block/base engine as the Lehman. The 380 cu in English Ford engine. I don't have one of these Lehman engines so I'll not be doing any research but LOTS of other guys on this forum do and they will want the facts mamm noth'in but the facts. So if it's only the fuel pump one would think ther'e must be a solution. If the pump lube is independent (and I believe it is) perhaps some heavy oil mixed w synthetics may keep the pump doing it's job. But then why did the engines Edelweiss describes endure lots of heavy loading, high speeds and long hours? May be others wondering too. Perhaps just some engines were affected and others manufactured at a different time had been "fixed". And if these engines were so bad how'ed so many get sold? And before you start Marin I don't think ther'e wasn't any others available.

 

[Marin]

As I wrote, the Dorset engine proved to be a good reliable engine in relatively low load, constant rpm service. In other words, as an engine in a slow boat. Or tractor or combine or crane, etc.

That is why Ford continued its production for years after it proved to be worthless as a truck engine, which was pretty much as soon as it was introduced. I'm sure it's not the first time a product was designed to fit a specific purpose, failed at it, but proved to very good for something else.

Are you sure the Sabre you mention was based on the Ford Dorset and not the Dover engine? I don't know the answer, but that may be why its injection pump was lubed by the engine. The Dorset's pump wasn't.

From what I've read and been told, the issue with the Minimec/Simms/CAV injection pump Ford used on the Dorset is it's simply a weak design. It breaks under constantly changing rpm use, particularly at higher rpm. In other words, truck use. At a constant rpm it obviously does okay as it usually goes quite awhile on a boat engine before needing to be rebuilt.

 

[av8r]

"That doesn't mean running it at maximum rated power is going to wreck the engine or shorten its lifespan which is measured in horsepower hours or weight of fuel burned. "

If an engine has a lifespan defined by horsepower-hours then operating at 50% power should double the operating hours, which seems to be what Marin is saying.

 

[psneeld]

"That doesn't mean running it at maximum rated power is going to wreck the engine or shorten its lifespan which is measured in horsepower hours or weight of fuel burned. "

If an engine has a lifespan defined by horsepower-hours then operating at 50% power should double the operating hours, which seems to be what Marin is saying.

I understand what both sides are saying and I have seen enough in life with mechanical things to agree with both.

I believe Rick is saying that a manufacturer builds and engine, tests it and gives operating parameters that should ensure good service life...at the rated RPM...there's no exact number given before major overhaul but there are some "general numbers" thrown around for different situations.

I also understand and agree with Marin (Plus Rick reinforced it in one post also)...that "out in the field" over a given length of time, the user groups communicate and seem to find the glitches in equipment that sometimes the manufacturers don't always address. The Lehman user/repairer group realized that the Lehman couldn't cut it as a truck engine but could in some applications as long as it was mostly run at no where near it's rated RPM for long periods of time.

Depending on what scenario you are in...you roll the dice and take your chances.

For me it's easy...my primary concern is fuel economy. Running my engine trying to get a knot or two more causes more grief than help...so my decision to run my Lehman around 16-1800 is a no brainer.

But I know that reducing power doesn't necessarily mean a thing in terms of longevity for the most part except for what marin has passed along about Lehmans. When I had my Cats I ran them 200 RPM less than max and they outlived most diesels at those numbers and the Detroits in a tug I ran for years were at the pins all the time.

 

[Marin]

If an engine has a lifespan defined by horsepower-hours then operating at 50% power should double the operating hours, which seems to be what Marin is saying.

No, I'm not saying the operting hours would be doubled. Just that I believe that taking it easy, within reason, on an engine will extend its service life vs running it hard all the time. Metal is affected by heat, pressure, and so on and I think it's pretty obvious that the service life of that metal will be longer if the stresses, heat, etc. it is subjected to are lower.

Now everyone says "the engines are designed to 'take it.'" But nobody can define "take it" in terms of longevity other than to say the engines will take it until they fail. Which tells me nothing if what I'm interested in is getting the maximum service life out of the engine.

But I have-- as I'm sure many of us on this forum have---- all sorts of evidence amassed over decades of operating and in many cases maintaining and repairing engines--- aircraft, outboard, inboard, vehicle, construction equipment, gas, diesel--- some mine, some other people's. In my case these engines went for years and years or hours and hours or miles and miles pretty much trouble free because they were operated conservatively. As compared to examples I've seen or know of of the same types of engines that had much shorter service lives because they were worked hard.

I have no more way of knowing exactly how long an engine's service life will be extended by operating it conservatively than other people know how long the same engine's service life will be when operated hard. All I can go on is what I and people I know have experienced. I could list some of the examples that I've experienced personally but obviously my examples only apply to my examples. But from them, and other's examples, I have concluded without a doubt in my mind that taking it easy on an engine will yield a longer service life assuming the same degree of service and maintenance.

This does NOT mean I don't use all the power available when it's needed. But it's not needed most of the time. In fact most of the time the power needed to do the job is significantly less than full or even high power. Particularly in the case of our boat.