Engine loading

[cardude01]

Reading an article on engine loading where it recommends folks with lightly loaded engines should try to run the engine at around 75% of continuous rating to prevent glazing. Or if you can’t do that run it for high RPM/high loading every once in awhile to prevent cylinder wall glazing.

Excerpt:

“OK, now we know to run our engines hard to make them last, but how hard? Here I will defer to boat mechanical guru Steve D’Antonio, who recommends that diesels should be run regularly at about 75% power.

(By the way, you need to set the RPM at way higher than 75% of wide-open throttle RPM to actually load your engine at 75%.)

Now that doesn’t mean that to keep our engines healthy we must run them all the time at exactly 75% power. We don’t need to fixate on an exact number here. Rather we need to:

run at high power settings regularly,
and avoid running at less than about half power for long periods.”

I think I knew all this at one time, but I guess I forgot, because after installing the steady sails I have found myself pulling the throttle WAY back when I have some good wind to reduce engine noise and fuel burn but keep the same speed, usually around 6.5 knots at around 1800 RPM.

The problem with this (according to the article) is 75% of my continuous rating of 3100 RPM is 2325, so I’m not doing my engine any favors going so slow evidently. I’m heading for the Bahamas in June so I don’t want to run it too slow for long periods of time like I have been.

If I still want to enjoy my slow, quite 1800 RPM cruise how often (and what duration) should I run the engine up to a higher RPM, and what is that higher RPM? I really hate running it at 3000 plus.

What about changing the pitch of the prop to load the engine a little more? Dangerous I know if I decide I want (or need) to run faster for some reason after overpropping, but just wondering if any here have considered this?

I have a 110hp Yanmar 4jh4-HTE with max RPM of 3200 and a continuous rating of 3100. My boat weighs about 24000 LBs and has a 35’ LWL so a hull speed of 7.9 knots.

This engine seems to be way too big for this boat IMO, since trying to run at hull speed digs a big hole and it’s way too damn noisy with the engine right under the PH.

 

[DavidM]

I disagree that marine engines should be run at 75% power regularly.

Take an extreme case of the QSB 5.9 480 hp engine. 75% is 360 hp. That engine would be lucky to last 1,000 hours at that rate which is 61 hp per liter.

Let me paraphrase Tony Athens who runs the biggest marine diesel shop on the west coast: “I have never seen a marine diesel damaged by running slow”.

He goes on to say that a modern high output marine diesel can usually be run continuously at up to 40 hp per liter and get decent life.

On the lower end most experts say that running hard enough to get the coolant and lube oil up to operating temps is sufficient. That usually takes about 10 hp per liter. Running slow can cause soot buildup and a run up to 75% for ten minutes every day or so will blow it out. Common rail engines because of their more precise fuel injection rarely need to do this.

So for your engine which is 2 liters I think, you can run at 20 hp up to 80 hp. But I would keep it well below 80 continuously.

David

 

[cardude01]

Oh ok. So at 1800 RPM it’s putting out about 40HP, so that won’t hurt it long term? As long as I run it up to 75% for ten minutes per day to blow out soot or “deglaze”?

And I’ve not noticed any smoking issues on my engine or anything, so I don’t *think* it’s been hurt.

 

[BIG CAT]

There are a lot of variations from mfg to mfg when it comes to diesel engines. So you will want to refer back to the recommendations of the mfg. At cat we generally recommend they be loaded to 30% or higher to prevent glazing. That doesn't mean you can run lightly loaded for say 8 hrs or longer. I primarily do generators and they typically see 20 to 30 hrs a year at most and those hrs will be at light to no load. when we ramp them up to full load. It normally only takes about 15 min. for the stack to clean up. So you will need to find a happy medium between normal operation and running it at higher load to prevent glazing. I will say newer electronic engine handle light loading better than the older mechanical engines.

 

[Nomad Willy]

Dude,
Look at the thread about repowering. It’s actually in General Discussions ??

There’s two JH Yanmars.
One is rated at 3800rpm and the other at 3000. If you have the 3000 engine you’re underpropped and if you have the 3800rpm engine you’re significantly overpropped.

I’d de-pitch re the latter right away and just run the 3000 rated engine. Since adding 1” of pitch would probably give you a 2800rpm WOT engine speed (overpropped) and the prop shops don’t do what’s really best for your engine (to add 1/2” of pitch) can’t be done I’d just stay w the 3200rpm top engine speed. With a little fowling on the prop and some on the bottom (typical condition) you’d probably be propped just right. This is assuming you have the 3000rpm rated engine.
With the 3800rpm rated engine you need to get the WOT rpm up to 3700 rpm minimum and 4000 max or very close to.

The above is my opinion and many will disagree but I think all the engineers in the field will agree. I am not an engineer. The engineers you would be best listening to are employed by engine manufacturers.

 

[Rufus]

So let's say the engine bores become glazed over time. What's the procedure to fix it? Is it as "simple" as pulling the head(s), pulling the pistons and running a hone down the bores? Would the rings have to be replaced to get them to bed or could they be reused? I believe this is likely a common issue with boosted engines like the 3208TA idling along at trawler speeds. An in-the-boat procedure would sure beat engine removal...but what is it?

 

[cardude01]

Dude,
Look at the thread about repowering. It’s actually in General Discussions ??

There’s two JH Yanmars.
One is rated at 3800rpm and the other at 3000. If you have the 3000 engine you’re underpropped and if you have the 3800rpm engine you’re significantly overpropped.

I’d de-pitch re the latter right away and just run the 3000 rated engine. Since adding 1” of pitch would probably give you a 2800rpm WOT engine speed (overpropped) and the prop shops don’t do what’s really best for your engine (to add 1/2” of pitch) can’t be done I’d just stay w the 3200rpm top engine speed. With a little fowling on the prop and some on the bottom (typical condition) you’d probably be propped just right. This is assuming you have the 3000rpm rated engine.
With the 3800rpm rated engine you need to get the WOT rpm up to 3700 rpm minimum and 4000 max or very close to.

The above is my opinion and many will disagree but I think all the engineers in the field will agree. I am not an engineer. The engineers you would be best listening to are employed by engine manufacturers.

This is my engine

 

[bayview]

Some people used to pour ajax in the air intake to scuff up cylinders.

 

[bayview]

Loading is related to prop demand and not linearly related to RPM. It is an exponential curve. Load = (RPM/maxrpm)^2.5

 

[Ski in NC]

Often the glazing is not really wear on the liner, but the hone grooves get packed with carbon. Oil control gets sloppy. Often a good hard run will burn the carbon out of the grooves and all is well. An hour or so at 75% should do it.

A 2liter engine at 1800 and making 40hp is not going to have a glazing problem. Even at 20hp at 1800 it will be fine.

It can be a real problem on gennies that run all night and all day at almost zero load at 1800, day after day.

But the issue still is rare. Running a Yanmar JH at hull speed is NOT going to have this problem.

Still good to run it hard once a day. But no need to go to full power, 75% should be fine. Even 50% should clean it up.

CD, don't worry about this.

 

[cardude01]

Often the glazing is not really wear on the liner, but the hone grooves get packed with carbon. Oil control gets sloppy. Often a good hard run will burn the carbon out of the grooves and all is well. An hour or so at 75% should do it.

A 2liter engine at 1800 and making 40hp is not going to have a glazing problem. Even at 20hp at 1800 it will be fine.

It can be a real problem on gennies that run all night and all day at almost zero load at 1800, day after day.

But the issue still is rare. Running a Yanmar JH at hull speed is NOT going to have this problem.

Still good to run it hard once a day. But no need to go to full power, 75% should be fine. Even 50% should clean it up.

CD, don't worry about this.

Excellent! Thanks!

I will cross this off my worry list. [emoji23]

 

[Rufus]

Often the glazing is not really wear on the liner, but the hone grooves get packed with carbon. Oil control gets sloppy. Often a good hard run will burn the carbon out of the grooves and all is well. An hour or so at 75% should do it.

A 2liter engine at 1800 and making 40hp is not going to have a glazing problem. Even at 20hp at 1800 it will be fine.

It can be a real problem on gennies that run all night and all day at almost zero load at 1800, day after day.

But the issue still is rare. Running a Yanmar JH at hull speed is NOT going to have this problem.

Still good to run it hard once a day. But no need to go to full power, 75% should be fine. Even 50% should clean it up.

CD, don't worry about this.

But let's say you have a big turbo 3208 like in my example, and the bores are indeed "glazed" ...not just loaded up with carbon in the hone grooves. The 3208 is not a sleeved engine. Would honing the bores with the engine in the hull be a viable procedure (assuming the bores are still round)? If so, would the rings have to be replaced or would they bed OK? (I don't have 3208s, but always wondered about the mid 80's oversized, mechanically controlled turbo engines slobbering around at hull speed).

 

[Ski in NC]

If you have high blowby and oil use, and hard running does not fix it, then yes you can hone and get decent results. You will never get a factory hone type surface finish, but it can get close enough to bed in new rings. But you absolutely want to go back with new rings. Better yet ditch the 2-ring piston and go with the 3-ring piston.

 

[Coastal Cruiser]

I don't think Load Factor is necessarily determined by throttle position. 50% throttle, (50% of WOT RPM) is not 50% Load.

Load is fuel being burned as a percentage of maximum fuel burn at WOT. At 50% throttle, which for me is 1250 rpm, the load is less than 30%.

From John Deere:
Load Factor Defined: * Load factor is the actual fuel burned over a period of time divided by the full-power fuel consumption for the same period of time. For example, if an engine burns 160 liters of fuel during an eight-hour run, and the full-power fuel consumption is 60 liters per hour, the load factor is 160 liters / (60 liters per hour x 8 hours) = 33.3 percent.

Re periodically running at high load: From John Deere 4045AFM85 owners manual: ...in a trawler propulsion application increase the throttle to achieve break in speeds (within 200-300 rpm of WOT) for a minimum of 10 minutes every 3 hours.

To me 10 minutes every three hours is not a big deal. It allows me to confirm, among other things, that the engine can achieve rated rpm and that the cooling system is working.

 

[sunchaser]

It would be interesting to hear some first hand details and information on a 4 stroke propulsion engine that has suffered from "under loading".

My take is that if your base engine is designed for genset service at 1500-1800 RPM, operating in this RPM window and at 30 to 50% of this base engine gen set load will negate any worries about "glazing".

That said, continually operating at rated coolant temperatures with oil temps above 185F seems relevant as well.

 

[Coastal Cruiser]

More from John Deere re engine M ratings, which are based on the ISO/SAE standards cited. There is so much "lore" out there regarding this stuff.

M ratings Ratings are based on the ISO 8665/SAE J1225 standard power rating and the ISO 3046/SAE J1995 crankshaft power rating. The M rating definitions are provided as a guide to help in the selection of the engine that best fits the application requirements.
M1 The M1 rating is for marine propulsion applications that may operate up to 24 hours per day at uninterrupted full power and have load factors greater than 65 percent. Possible applications: Line haul tugs and towboats, fish and shrimp trawlers/draggers, and displacement hull fishing boats.
M2 The M2 rating is for marine propulsion applications that typically operate between 3,000–5,000 hours per year and have load factors up to 65 percent. This rating is for applications that are in continuous use and use full power for no more than 16 hours of each 24 hours of operation. The remaining time of operation is at or below cruising† speed. Possible applications: Short-range tugs and towboats, long-range ferryboats, large passenger vessels, and offshore displacement hull fishing boats.
M3 The M3 rating is for marine propulsion applications that typically operate between 2,000–4,000 hours per year and have load factors up to 50 percent. This rating is for applications that use full power for no more than four hours out of each 12 hours of operation. The remaining time of operation is at or below cruising† speed. Possible applications: Coastal fishing boats, offshore crew boats, research boats, short-range ferryboats, and dinner cruise boats.
M4 The M4 rating is for marine propulsion applications that typically operate between 1,000–3,000 hours per year and have load factors below 40 percent. This rating is for applications that use full power no more than one hour out of each 12 hours of operation. The remaining time of operation is at or below cruising† speed. Possible applications: Inshore crew boats, charter fishing boats, pilot boats, dive boats, and planing hull commercial fishing boats.
M5 The M5 rating is for marine recreational propulsion and certification for light-duty commercial Tier 3 applications that typically operate up to 1,000 hours per year and have load factors below 35 percent. This rating is for applications that use full power for no more than 30 minutes out of each eight hours. The remaining time of operation is at or below cruising† speed. Possible applications: Recreational boats, tactical military vessels, and rescue boats.

† Cruising is any operating time where the engine speed is more than 200 rpm less than the maximum attainable engine speed.

 

[BIG CAT]

But let's say you have a big turbo 3208 like in my example, and the bores are indeed "glazed" ...not just loaded up with carbon in the hone grooves. The 3208 is not a sleeved engine. Would honing the bores with the engine in the hull be a viable procedure (assuming the bores are still round)? If so, would the rings have to be replaced or would they bed OK? (I don't have 3208s, but always wondered about the mid 80's oversized, mechanically controlled turbo engines slobbering around at hull speed).

"Glazing" the cylinder walls will not make the crosshatch disappear. It they are gone it's wore out.

 

[Rufus]

So what exactly is "glazing"? Simply carbon buildup on the cylinder walls, or something wear related?

 

[DavidM]

My understanding is that glazing is a hard thin film consisting of polymerized unburned fuel and soot which sort of acts like fiberglass and resin together.

It is thin but enough to fill in the hone marks. Exactly why it results in oil burning I don’t know. I think FF had a good theory.

Running hard for a few hours sometimes burns it off, but if not a light honing will take it off.

David

 

[BandB]

Go to the engine manual. If you can't locate one then the manufacturer. Now beyond that, we are probably among the few here who consistently run high powered engines at 70-80% load, which is typically 90% RPM or so, and I think the warnings that you're going to damage your engine by not running it at 75% are greatly overstated for most engines. Have your engines shown signs of heavy smoke or soot when running where you run them or signs of buildup of carbon impacting performance? If not, you've likely done fine. Now, my recommendation is every six hours of running to run at 50-75% load for 10 minutes or so but I don't feel strongly that is a requirement, just probably helpful.

Listen to and observe your engine. Then you'll get a feeling if it needs to be run harder for a bit. But don't panic over reading that. If you were running a high performance boat, it would be essential. But not for most on here.

 

[BruceK]

So let's say the engine bores become glazed over time. What's the procedure to fix it? Is it as "simple" as pulling the head(s), pulling the pistons and running a hone down the bores? Would the rings have to be replaced to get them to bed or could they be reused? I believe this is likely a common issue with boosted engines like the 3208TA idling along at trawler speeds. An in-the-boat procedure would sure beat engine removal...but what is it?

Well Rufus,I run my ubiquitous Lehman 120s at 1400-1500 rpm, sometimes less in some specific areas, and I`ve never seen any evidence of glazing.
However, shortly after purchase in 2010, not realizing the eutectic fridge/freezer compressor had died, I ran the Onan MDKD 6.5 unloaded for an extended period and definitely glazed it, lots of blue smoke which would not go away. I fixed it using Nulon oil additive added at double strength as per it`s makers advice, and (stop that sniggering please!) it worked. I now add a normal dose at oil changes just in case I underload it. Still runs well 9 years on, it burns very little oil. If I saw a need I`d happily use it in the Lehmans, but I don`t.
I also took glucosamine(which my orthopedic surgeon terms "a placebo at best")daily for at least as long,and have enough arthritis in at least one knee to lead one day to a TKR. Not all "snake oils" are created equal.

 

[Lepke]

My current boat came with 2 generators. An Onan (Cummins 3A1-7) 3 cylinder 14kw and a Perkins 4108 14kw. One or the other had been run continuously cruising or anchored. Mostly light loads. Both were 1800 rpm sets. Both were badly glazed and burned oil. I lightly honed and crosshatch hones and installed new rings. Also had the heads rebuilt. That stopped the oil use, engines start fine in cold weather. In the past I ran several engines thru several rebuild cycles and rebuilt other engines where I knew the history.
It depends on the engine and rpm. Heavy duty engines like Detroits and bigger Cats & Cummins don't seem to be bothered by long hours at light loads. Especially 1200 rpm generators. Trollers often go days at slightly above idle. Tuna jig boats can go a couple weeks at half throttle. I've done it without glazing.
The bigger harm is high exhaust gas temperatures on turbo engines run flat out.

 

[Arun52]

I have worked on engines from many different manufacturers in all types of machines and generators.
Lots will slobber when insufficiently loaded.
On generators load banks are often installed to make them work hard enough.
I had a new crane engine recently that was particularly bad and this was the response I got.

“These comments are from Mercedes (MTU)”
“Wet stacking is when the rings have not bed into the cylinder bore and it allows oil to pass the rings and out of the exhaust.
This is common for engines that operate at low load with low engine hours.
Engines require boost pressure to push the rings against the bore and “wear in”, boost pressure is created with Revs and engine load.”
“I would recommend packing the machine up and taking it for a good drive making sure that the engine is made to work hard.”

 

[Simi 60]

That said, continually operating at rated coolant temperatures with oil temps above 185F seems relevant as well.

I have heard this mentioned but have not found any documentation stating it.

At our usual 7.5 kn @ 1150rpm we are always on temp for water but oil temp is 167f / 75c
Even running at 8.5kn @ 1250rpm temps don't go much more than 176f / 80c
Any more than this just wastes fuel big time.

 

[Rufus]

Well Rufus,I run my ubiquitous Lehman 120s at 1400-1500 rpm, sometimes less in some specific areas, and I`ve never seen any evidence of glazing.
However, shortly after purchase in 2010, not realizing the eutectic fridge/freezer compressor had died, I ran the Onan MDKD 6.5 unloaded for an extended period and definitely glazed it, lots of blue smoke which would not go away. I fixed it using Nulon oil additive added at double strength as per it`s makers advice, and (stop that sniggering please!) it worked. I now add a normal dose at oil changes just in case I underload it. Still runs well 9 years on, it burns very little oil. If I saw a need I`d happily use it in the Lehmans, but I don`t.
I also took glucosamine(which my orthopedic surgeon terms "a placebo at best")daily for at least as long,and have enough arthritis in at least one knee to lead one day to a TKR. Not all "snake oils" are created equal.

I got me a TKR about a year and a half ago. Currently about 95%. My Doc doesn't use off the shelf replacement parts. Ordered up a digital scan of the original and had the new one cast and machined to original specs. Get it done, man. But be careful about using that freakin' opioid pain medication. I used it sparingly for a week and it shut down the ol' plumbing...far bigger problem than the lopped off knee. I was single handing the boat across Lake Michigan four months after the overhaul. Get it done!

Nulon additive. I've added it to my boat notebook.

 

[DDW]

There are literally millions of light trucks with diesels in them, running literally billions of miles and hours, nearly all of them lightly loaded most of their lives.

 

[sunchaser]

I have heard this mentioned but have not found any documentation stating it.

At our usual 7.5 kn @ 1150rpm we are always on temp for water but oil temp is 167f / 75c
Even running at 8.5kn @ 1250rpm temps don't go much more than 176f / 80c
Any more than this just wastes fuel big time.

Yes, it is tough to get oil temps up on some lightly loaded engines. Many articles by manufacturers and our own Steve D on the reasons for having oil temperatures in the 185 to 195 F range. Or one can use simple logic, water boils at 212F. What is in oil we don't like - things like water, fuel and acids.

Very common for better marinized engines to have a coolant to oil heat exchanger which allows oil to be heated significantly during colder water applications. My engines have these. With water temps of 55F and under light load the oil is 185F minimum. Diesel fuel begins to volatilize at 140F, rate increasing as temps rise.

Older marine diesels use raw water oil coolers, tough to get healthy oil temps this way in cooler waters for a lightly loaded diesel.

 

[FF]

So what exactly is "glazing"? Simply carbon buildup on the cylinder walls, or something wear related?

The cylinders get burnished (polished) smooth..

The problems come from the fact that the piston rings seal because of combustion gasses behind the rings forcing good contact.

This only happens hen there is a good load , the piston resists going down , and the combustion pressure behind the rings is high enough to force a good ring seal.

With little pressure the rings burnish the cylinder bore smoothing out the honed oil holding scratches.

I believe the 75% load is a correct concept ,to gain a good seal, but it must be 75% of the power available at the operating RPM , nothing to do with WOT and a screaming engine.

A look at an engine HP graph with a theory prop load shows the problem big time.

At most cruise RPM the engine is very lightly loaded on displacement hulls..Sometimes 20-30% of available power.

One costly solution would be a CPP controllable pitch prop to increase the load it lower RPM.

Almost as good would be a 2 speed transmission to speed up the prop at low RPM to increase the engine load . Either would help fuel use.I believe GB does this on some boats.

A "cruising prop " that is created to operate with better loading at normal cruise would also solve the problem ,
but an EGT gauge and some knowledge would be required to run the boat.

Simplest would be a throttle stop at a loading that would work, even in heavy weather , with no overload.

Last choice is a hard high RPM fuelish run to burn out the carbon deposits that collect behind the rings and harden and eventually seize the rings.

For most vessels if the boat assembler had chosen a less powerful engine there would be less problem with a slobbering engine where all oil control has been lost.

For those with the ability to have a boat built , the combination of a CPP with two engines coupled to a center single shaft would seem ideal.

For the military ,the needed trannys have been built for the last 6-7 decades and either or both engines can be operated as desired.


For most folks screaming the engine at WOT in bogus Manatee Zones is about all that is possible.

 

[sunchaser]

The question remains, who has first hand details on the early demise of a 4 stroke newer marine propulsion engine due to being "lightly" loaded? Myth, fact, dock talk, rare exception, reality or what?

 

[cardude01]

If I was building a new trawler or motorsailer, I think I would spring for a CPP.

http://www.kastenmarine.com/CPprops.htm#RATIONALE