Wide Open Throttle

[bobofthenorth]

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.

 

[psneeld]

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.....

 

[rwidman]

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.

 

[Edelweiss]

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.
Larry B.

 

[RickB]

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.

 

[Pineapple Girl]

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.

 

[Marin]

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.

 

[Nomad Willy]

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.

 

[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.

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.

 

[FF]

"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.

 

[rwidman]

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.

 

[rwidman]

...............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.

 

[RickB]

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.

 

[Marin]

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.

 

[skipperdude]

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?

SD

 

[Marin]

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.

 

[bobc]

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?

 

[RickB]

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.

 

[Marin]

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.

 

[bobc]

Egt

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.

 

[RickB]

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

It is important to know where the temperature is taken if comparisons are to be made.

 

[Marin]

Our EGT probes are mounted in the exhaust elbows just aft of the connection to the exhaust manifold and prior to the water injection point. Our EGT sensors and gauge are by ISSPRO.

 

[sunchaser]

This summer the after cooler on one of our Perkins Sabres developed a leak allowing sea water into the induction air. I bypassed the after cooler and ran about 1000 miles with no ill effects on either EGT or a variety of engine temps as measured with an IR gun. On advice of the designer I limited max RPM to an EGT of 600 F or about 80% of full rated load equating to 2000 RPM. 2000 RPM I never hit anyway with normal cruise about 1750 RPM and 400 F EGT.

This issue caused me to once again visit the belief that unless a marine engine can achieve max rated RPM without over heating, something is amiss whether in engine health or prop size. For sure, one of the boxes to be checked when buying or selling is "Max rated RPM achieved OK?"

In my pre-retirement years, the last big diesels I bought were 4000 HP and rated for full RPM at 15,000 feet for a 30 minute climb out of an open pit. This is how the engine designers have built most diesels for decades if not 70+ years or more.

So my thoughts, run them hard now and then to assess engine well being. The next owner sure as heck will prior to finalizing a purchase decision.

 

[Nomad Willy]

When I repowered I made a big deal of getting sea water off the engine completely. Never regretted it.
Wish you were down the street so we could swap sea stories Tom.

 

[Edelweiss]

This summer the after cooler on one of our Perkins Sabres developed a leak allowing sea water into the induction air. I bypassed the after cooler and ran about 1000 miles with no ill effects on either EGT or a variety of engine temps as measured with an IR gun.

___________________________________

Have you had any issues with the engine since leaking salt water through the air intake?

I had a dripping exhaust elbow joint over the air intake, 6.354 n/a, that went undetected for several weeks on a trip. After the joint was repaired, everything was fine for a while. Then we started hearing a slight compression hiss at idle. Thinking it was a head gasket, we pulled the head and found two of the hardened valve seats on the intake side had severe pitting.

Anyway something to watch for.
Larry B

 

[Delfin]

Thanks Marin. That is one for sure.

So anyone with an FL120 should follow your advice.

It seems that it is going to be an as per engine.

The Cat dealer is of a mind that it is a good thing to do once in a while.

Any others?

SD

SD, we don't run up to WOT because we can achieve a nice hot EGT at around 1750 rpm, and while there may be a reason to put a greater load on the engine, I don't know what that reason would be. So we cruise around 1375 - 1400 rpm at 550 degrees EGT (out), which probably means around 700-750 degrees inlet temperature, and 775 to 800 degrees (out) and probably 1100 degrees inlet temperature at 1750 rpm. I get a little visible smoke when I first spool up (which I do every 4 hours or so for 15 minutes), but that dissipates to being almost invisible after 5 minutes or so of loading. I don't know if this is the best way to manage the engine, but it seems to match what most experts recommend.

 

[honeybadger]

Talking to my local commerical guys, They refered me to a manual one of them had with the specs that the perkins should operate at 80% of max rated RPM during use. I know that all our military equipment " diesel " crank and after about 45 seconds runs up to almost WOT. Some times for 10 days at a time to provide power for the FOB's. they would fuel them and about every 10 days they would shut them down check coolant, Check the oil, Take a sample of the oil, Service it if hours were in range then fire them up again. i Never seen any of them fail running WOT one was at a FOB i worked at on two deployments so it had been there over 3 years doing its job. So i guess it's all in what the MFG says about the 80% range .

 

[Nomad Willy]

honeybadger,
Are you sure they spec'ed 80% of rpm? That would seem a dangerous thing for them to do as many boats are'nt propped right. The load on an overpropped boat would likely be WAY overloaded at 80% rpm. Also 80% of rated rpm on a correctly propped boat is about 50% engine load. This is a very low load for a max continuous rating. A 37 Plymouth could probably do that.

 

[Adelaide]

Don't forget that he makes a living selling engine parts.

A freshly washed car always seems to run a little better too.

Don't start rumors now.

 

[honeybadger]

The Yanmar FAQ area on the web says this:
Q- What is the definition of a LDC (Light Duty Commercial) application?


A- Any engine used in a revenue producing, government service or rental use is considered a non-recreational craft application and is not covered by the Yanmar Recreational Limited Warranty policy. Rental use is defined as a vessel used for pleasure charter, typically sailboats, sailing catamarans, power catamarans and trawlers. For an engine to be considered for a Light Duty Commercial application it must fall within the following guidelines:

• Engine is operated at maximum output for less than 5% of total operation hours.
• Standard operation is at less than 90% of the maximum output RPM.
• Wide open throttle RPM’s, under load, must reach rated speed in any operating condition. post rpm is max 3000 max load ,Continuous rating rpm listed as 2900. So as i say Who knows ??