Under loading.

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"It sort of sounds like the old adage to “blow it out…” I do this as it seems like cheap insurance and probably does no harm."

The only harm could be from , Blowing them out" and then shutting down too soon.

IF the EGT is really hot , the turbo will also be really hot.

It takes 3-5 min for the turbo to cool down to the temperature that will not cook the oil on shutdown.

Most folks entering a marina have lots of cooling time as they manuver,.so no problem.
 
Something that occured to me;

Keeping the oil temp up is the key to running w low loads but the most direct source of heat in the lube oil is not from fire in the hole or load on the engine. It's from friction. The oil goes to all the places where there is friction .... bearings and cylinder walls.

I wonder if one ran a diesel engine at high rpm and no load would the oil temp come up as high or higher than an engine under significant load at much lower rpm?

Lets say I under propped my boat 300rpm (3000rpm engine). In order to get enough power to push the boat I may need to run the engine much closser to max rpm. Maybe 2800. There would be very low forces on engine parts like crank bearings and cylinder walls but many more strokes to deliver the same power. Torsional vibration would be less as there would be more power strokes of lesser intensity. But the heat that gets into the lube oil would get there directly as friction on the bearings where the oil is in contact with the heated (from friction) bearings.

So rpm and the resultant friction may not be a better source for lube oil heat than combustion heat. The friction probably dosn't create enough heat to make upping the rpm a good way to keep one's oil warm.

If I was a serious underloader I'd be thinking of an oil cooler by-pass and as FF suggests very frequent oil changes. If an engine is well broken-in just keeping the oil temp up to 180F or so could insure a healthy engine despite almost constant low power output.
 
dhays said:
Given my general level of ignorance, I have thought membership at boatdiesel.com would be worthwhile.
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Dave & others...

To clarify for anyone considering BD
Membership is not req'd to access the website - you can even use the search function to see what articles / forum posts etc are available you are limited in the ability to open the actual articles, manuals, etc.

This allows you a "peek in the box" before committing to the membership.
My opinion agrees w/ others - even w/o specific engine info there is a wealth of info if you are looking to learn more about marine diesels.
 
Don,
And for me just thinking about all the information that was added after I left is motovation. Thanks for the reminder.
 
As for me, I went ahead and spent $25 enjoying BD. I am buying a new boat and want to make sure I understood as much as I could about larger diesel engines. I am a sailboat her and trawler engines are considerably different, not just larger. I think the $25 investment has handsome returns. Just reading the articles on the exhaust system and aftercooler alone will probably save me thousands of dollars.

My two cents

Gordon
 
Gordon J said:
As for me, I went ahead and spent $25 enjoying BD. I am buying a new boat and want to make sure I understood as much as I could about larger diesel engines. I am a sailboat her and trawler engines are considerably different, not just larger. I think the $25 investment has handsome returns. Just reading the articles on the exhaust system and aftercooler alone will probably save me thousands of dollars.

My two cents

Gordon
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Gordon, just FYI.....I am pretty sure when tony talks about your model of engine(and mine) he refers to them as 315hp because that is what it makes. Cummins did some weird metric power rating that they rated at 330. But I think SAE they make 315. There are older engines that people will say 315hp and are in fact 315hp...they are the same exact engine as ours except for a few accessories. You will also see the C series Cummins suffer the same nomenclature issue. Are they 450hp? I don't think so. I think they are 417. And some people round up to 420. Ski would be the one to clear this up.

And I think the Cummins manual says to load up engines one hour out of every eight hours if you are under loading. Again, I agree with Tony and everything said here. But just to give you an idea of what Cummins says under the pressure of warranty and marketing.
 
Gordon J said:
As for me, I went ahead and spent $25 enjoying BD. I am buying a new boat and want to make sure I understood as much as I could about larger diesel engines. I am a sailboat her and trawler engines are considerably different, not just larger. I think the $25 investment has handsome returns. Just reading the articles on the exhaust system and aftercooler alone will probably save me thousands of dollars.
Click to expand...

Gordon, I am in exactly the same situation. So far in my boating life an engine has been a necessary evil. I paid more attention to sail shape than engine performance and maintenance. That is going to change.

The boat I have an offer on has a Cummins QSB 5.9L 380hp engine. It is a high output engine with aftercooler and turbocharger. I found lots of information on not only this type of engine, but this specific engine on boatdiesel.com. So for me, it was worth the $25 for a year. To put it in perspective, that is less than the cost of one anode for me future engine. I figure it is a cheap resource to help further my education. May or may not renew it in a year, we will see.
 
Baker,

Thanks for the info. I was wondering why on BD I only found a 6BTA5.9 315 HP motor. Was not sure if that was mine. I need not worry about warranty as the boat is 13 years old with 1080 hours on the engines.

Dhays, which boat are you getting? Is it on Yacht world? I have not yet bough any zincs for the engines, but am prepared for sticker shock. My current volvo engine has no zincs, nor does my panda fisher 6KW genset. I have one zinc on my max-prop.

I learned after joining BD that the surveyors I used are the same he used when he brought a boat from Florida to the Virgins. He posted the results. I can tell you that the engine survey at $1000 made me blink, but I think well worth the money -- by a wide margin.

On renewal, I am having the same thought. We'll see how much I keep refering back to the site after closing on the boat.

Gordon
 
Gordon,

The boat I have an offer on is a North Pacific 43 located in Puget Sound. It is having a survey next Wednesday. I haven't bought zincs for the engine but I have priced them. My current Yanmar on my sailboat has no zincs in the engine.
 
Gordon:


Buy your engine zincs and your hull zincs from boatzincs.com. They don't have to come from Cummins. You just need to know the size- 1/4", 3/8", etc. Buy the zinc only rather than the zinc plus brass cap. And tighten the zinc with pliers so it won't unscrew and get stuck inside the exchanger.


David
 
Ski, a TF member and a mechanical engineer who now practices as a marine diesel mechanic, posted the following in reply to Gordon's thread on boatdiesel.

We now have two full time professional mechanics who are saying that under loading is not a problem on propulsion engines.

"Second Tony on this. In 20+ years in the engine business I have never seen a propulsion engine that suffered from light load running. Only two gensets that had high blowby from glazed cylinders, those probably never got any decent break in. But never seen an issue on a propusion engine.

Advocating 75% power is nuts. Most engines 20-30% keeps them happy. 75% is usually considered an upper limit for long term use, not a minimum. 75% is a good number for the end of the trip "clean out", though. No need at all to go to 100% unless you want to check for correct max rpm.

Running light will gunk up the exhaust manifold, piston crowns and turbo. But one hard run will clean that right up. Not an actual problem. It is cured when that cloud of smoke on power-up goes away.

If you power up and see little or no smoke, then engine was NOT gunked up from your previous light load run.

I have seen dry stack mufflers clogged with soot from light load running, enough to choke the engine and require muffler replacement or worse, a stack fire. But that only applies to dry stack, is rare, and usually causes no engine problem. Sometimes with careful hard runs we can "burn them clean", but have had to replace a couple mufflers."


David
 
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djmarchand said:
Only two gensets that had high blowby from glazed cylinders, those probably never got any decent break in. But never seen an issue on a propusion engine
QUOTE]

One thing I've always been told on marine engines is to go 100% by the book on break in and that's in many ways the most critical time in the life of your engine.
Click to expand...
 
BandB said:
One thing I've always been told on marine engines is to go 100% by the book on break in and that's in many ways the most critical time in the life of your engine.
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You are absolutely right. Here are the break in instructions from Northern Lights:

BREAK-IN PERIOD​

1. The first 100 hours on a new or reconditioned

engine are critical to its life and performance.
2. Operate the engine under various conditions,
particularly heavy loades with minimal idling, to
help seat engine components properly.
3. Constantly check the engine temperature and oil
pressure gauges (sets with Series 3 or 4 panels).
4. Oil consumption is greater during break-in as
piston rings take time to seat.​
​



These are fine as far as they go. But I really appreciated Jeff (I think his name was- at Bayshore Marine) cautioning me about maintaining load on the genset during break in and suggesting ways to do it as well as advice afterwards.

It was Jeff who told me that he keeps one guy busy removing gensets and honing the cylinders to fix those that have been run 24/7 in the Carribean over the winter when it really isn't needed. Maybe an exaggeration based on Ski's experience, but worth noting in any case. Gensets are different because while they run at decent rpms, there is often zero load on them.​



Nothing beats hands on practical experience from guys like Jeff, Tony and Ski.​

David​


 
All this talk about the unknowns of underloading. I suppose overloading isn't such a mystery since the mfg's post relatively clear guidelines regarding M1, M2 ratings, etc.
 
makobuilders said:
All this talk about the unknowns of underloading. I suppose overloading isn't such a mystery since the mfg's post relatively clear guidelines regarding M1, M2 ratings, etc.
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Underloading in the trawler world. Overloading in the performance boat segment.
 
I’m gratified that this subject has generated so much dialog and exchange of information and opinions. I have the greatest respect for Tony, I have corresponded with him on several occasions and I have been a commercial member of BD for many years. I respectfully disagree with some of his tips, including propeller nut installation order, it flies in the face of ABYC, USN, USCG and SAE guidelines (I write an entire column on this subject). I completely agree with his assessment of exhaust system issues being very problematic, (especially for heavily loaded engines). His website is a trove of valuable, practical information.

He acknowledges but downplays under loading issues, and I don't doubt what he says is accurate. His experience is with west coast vessels, mostly Cummins and a lot of commercial/fishing vessels, few of which putt about at low load, and because there are far fewer places to do this in that region. While on the east coast the intracoastal ww and many tributaries are low load havens.

I'm on different vessels every week with many different engines, Deere, Lugger, Cummins, Cat, MAN, MTU, 2 stroke DDs, Perkins, Westerbeke, Yanmar, Volvo, the gamut. All are recreational, most displacement some planing (and these run at displacement speeds most of the time), some dry stack, a few sail. Again, different than Tony’s experience and perhaps that of other cited diesel mechanics.

The effects I'm seeing, when I see them, the effects I write about and photograph, don't typically stop an engine per se, they are more insidious, they lead to rough running, smoking, poor fuel economy, fouled injectors and turbos and long term potential for oil starvation and thereby premature wear of lubricated parts, that are often not directly attributed to chronic under loading.

These aren't offset by the occasional high speed run, you can't turn the clock back on hundreds of hours of low load soot and varnish accumulation with one high speed run. I advocate a periodic heavier load for 10 mins out of every 4 hours. This is in no way harmful to any diesel engine unless it has other issues. BTW, Cummins and other manufacturers make continuous duty engines that are designed to run at 100% load 100% of the time, other ratings limit 100% load to 10 minutes, it varies from engine rating to engine rating.

You can cast about for opinions until you find the one that fits your view and experience, I don't fault anyone for doing this, it's reasonable. I'm simply reiterating that my observations, and the articles I write based on them, are based on my own first-hand experience, which I’ve only augmented in this case with input from engine manufacturers and volume re-builders.
 
Hi Steve,

From the little that I understand, I don't think that you would get much of an argument from Tony Athens on a higher loading for 10 minutes every few hours. Few of us have the luxury of specifying the engine that is in our boats. We buy a boat that will best meet our needs and it is an exercise in compromise.

I am looking at buying a boat and the one that I have an offer on has a larger engine than I wish it did. However, the Cummins QSB 5.9L is very common in SD hulls of this size. As an owner, I will be balancing a number of factors when selecting a throttle position. Fuel burn will be an important one. The prior owner ran the boat at typically 10 knots from what he told me. He would have burned 3-4 times the fuel as he would have at the more sedate 7 knots that I anticipate. He has, literally, money to burn. I don't. So as a future owner I will have to balance current operating costs, with potential future rebuild or maintenance costs. So while it might be "best" for engine life to run at 50-70% loading for most of the time, I will likely end up running at about 30% load much of the time. However, based a lot on what I have been learning from folks with actual experience like you, I will also try to modify my use in ways to try and be a little easier on the engine.
 
Dave you're in the drivers seat now as a shopper. When you actually buy a boat you will no longer be in control. For the most part. Of course you can buck up and run 50 to 65% load w no need to blow out any black stuff or whatever you want but the fallout will be on you. I'm not that familar w what boat you're looking at and what the options would be if you bought it. And there are few SD boats out there power loaded ideally for slow running. The single engine GB36 or 42 comes to mind. When boats are bought new the people buying them have plenty of money for fuel at any speed but as they get old and cheap people who buy them have limited money for fuel.

But there are boats out there that are propperly powered for slow running. Even some from the 70's. You gotta shop rather hard to find them though. If I were you, and of course I'm not, I'd find some boats that are powered for what you want to do. And when you buy such a boat participation in discussions such as this thread you can participate w nothing to loose. Just take part because it's interesting.
 
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dhays said:
Hi Steve,

From the little that I understand, I don't think that you would get much of an argument from Tony Athens on a higher loading for 10 minutes every few hours. Few of us have the luxury of specifying the engine that is in our boats. We buy a boat that will best meet our needs and it is an exercise in compromise.

I am looking at buying a boat and the one that I have an offer on has a larger engine than I wish it did. However, the Cummins QSB 5.9L is very common in SD hulls of this size. As an owner, I will be balancing a number of factors when selecting a throttle position. Fuel burn will be an important one. The prior owner ran the boat at typically 10 knots from what he told me. He would have burned 3-4 times the fuel as he would have at the more sedate 7 knots that I anticipate. He has, literally, money to burn. I don't. So as a future owner I will have to balance current operating costs, with potential future rebuild or maintenance costs. So while it might be "best" for engine life to run at 50-70% loading for most of the time, I will likely end up running at about 30% load much of the time. However, based a lot on what I have been learning from folks with actual experience like you, I will also try to modify my use in ways to try and be a little easier on the engine.
Click to expand...

To me, it's all about condition and how it surveys. The fact you'll be running it mostly at 30% load doesn't concern me. You can go faster occasionally just to keep a smile on it's face. However, there are plenty of other things to check out on the engine that are more worrisome than what load you intend to run. Just don't let all this talk discourage you from choosing it if it's the right boat for you.

And, someone mentioned all the talk about low load and none about high. Well, I lived on a lake until 2012. Far more problems there with high load. There were people who only knew wide open throttle. I've seen a dealer go through great detail on proper break in and then seen the boat out racing ten minutes after it pulled away. I know one dealer who on high performance boats wouldn't deliver them until he'd done some initial break in because he knew people buying fast boats often just couldn't wait. I was also amazed how well many of the engines took the abuse they received.
 
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Here is some interesting info from another engine expert about oil, temperature and light loading.......:D


First off, the reason a certain minimum oil temperature is desirable is because oil is designed for a certain viscosity at normal operating temperatures. Proper lube oil flow (pressure and rate) requires a certain viscosity to obtain. Too high a temperature and the oil is too thin to handle high loads. Too low a temperature the oil will either not flow or it will not flow at a rate high enough to maintain bearing clearances at high loads.

Cold oil at low loads is not a disaster. When engines are run at low loads, the internal friction of the oil itself is reduced so less heat is produced, less fuel is burned so less heat is produced and transferred to the oil but since loading is low the flow rate requirement is also reduced and oil pressure is probably higher due to the increased viscosity. Low oil temperature may mean the engine is not operating at its highest efficiency because it takes more power to move the oil around and drag created by higher viscosity oil is greater ... so less power goes to the shaft than with hot oil. So what? The engine is operating at low load, what is there to lose?
 
Why is it that turbochargers have made under loading such a problem. Eric you say that single engine Grand Banks would not be a problem with under loading at moderate rpms and I agree. These were first delivered with Ford Lehman engines and later with Cummins 6B engines. Both engines are approximately 6 liters.


So fast forward to today where Dave is considering a boat with a Cummins QSB 380, also a 6 liter engine. The only difference between it and the Lehman is a high output turbo charger and an after cooler. The only difference between it and the Cummins 6B is a higher output turbo charger and a sea water after cooler.


Why does the addition of a turbo charger and after cooler or a higher boost turbo charger and a sea water after cooler mean that the QSB will be "under loaded" at moderate rpms and will carbon up, but the two older engines won't? All three engines will produce the same power to go the same speed in a GN 36 or similar hull.


It seems that Steve is focusing on percentage of rated power to determine whether an engine is under loaded and not actual hp per liter produced which I believe is the correct way of looking at it. I believe that any marine engine loaded to 10 hp per liter will not be under loaded.


David
 
Here is some interesting info from another engine expert about oil, temperature and light loading.......:D


First off, the reason a certain minimum oil temperature is desirable is because oil is designed for a certain viscosity at normal operating temperatures. Proper lube oil flow (pressure and rate) requires a certain viscosity to obtain. Too high a temperature and the oil is too thin to handle high loads. Too low a temperature the oil will either not flow or it will not flow at a rate high enough to maintain bearing clearances at high loads.

Cold oil at low loads is not a disaster. When engines are run at low loads, the internal friction of the oil itself is reduced so less heat is produced, less fuel is burned so less heat is produced and transferred to the oil but since loading is low the flow rate requirement is also reduced and oil pressure is probably higher due to the increased viscosity. Low oil temperature may mean the engine is not operating at its highest efficiency because it takes more power to move the oil around and drag created by higher viscosity oil is greater ... so less power goes to the shaft than with hot oil. So what? The engine is operating at low load, what is there to lose?

I am no engine guy but I do know the backyard mechanic suggestions/theories to be way off base and those suggested by engine pros and how they mirror the vessel engineers I work with on commercial vessels. Take heed of the above and what Ski and few others post. Try and sort out the guys who keep trying to match marine engines with their cars.
 
djmarchand said:
It seems that Steve is focusing on percentage of rated power to determine whether an engine is under loaded and not actual hp per liter produced which I believe is the correct way of looking at it. I believe that any marine engine loaded to 10 hp per liter will not be under loaded.
Click to expand...

Interesting point that I hadn't really thought about. The Turbo enables higher HP for a given engine displacement.

I am really not concerned about using the QSB 5.9L at low power settings at this point. This particular engine has performed very well in this application for a number of years. However, the discussion has definitely improved my understanding of diesel engines in general.
 
Interesting thread. I was rereading the operation and maintenance manual for the Cummins 6bta last night, and found a couple of things of interest. There is a warning not to operate at slow idle after a cold start for more than 10 minutes, citing the consequences discussed here. There is also a warning against extended operation below normal operating temperature, which is 181 - 203 Fahrenheit. That's all I could find regarding this subject.

One other interesting finding is that in this motor the oil cooler is in the fresh water cooling loop. So I'm not going to lose any sleep over not measuring oil temperature. In a steady state of operation oil and coolant temperature will always be very close to one another.

My conclusion from this and the various points raised here is that if I run my 6bt within the specified operating temperature (as measured by coolant temp) in steady state operation it is not going to suffer from any negative consequences related to underloading.
 
Versions of the Cummins 5.9 fitted here appear to have rated outputs from 220hp to 380hp. Is the engine underloaded if the turbo and associated tweaks to increase max output are not fully employed? It`s still the same block and head, maybe with a few power increasing tweaks.
 
That kinds of bring everything back to simply measuring temperature of the operating engine with an IR thermometer. If the oil pan, transmission, coolant jacket are all at the desired temperature in normal operation, I don't think I would lose any sleep over it. My engine has 4800 hrs on it. The last 5 years under the previous owner it never went over 1600 rpm. Rumor had it that there was a throttle block that was put in by the previous previous owner when it was in a charter fleet. Being somewhat mechanically inclined I discovered the problem was a binding throttle cable which was corrected in about 5 minutes with some spray lube (I have a spare if I need it). On the first WOT test, the engine spooled up to 2650 RPM and the boost gauge went up over 20 PSI. The previous owner didn't think the boost gauge worked. During the high speed run I didn't see any black smoke coming out the back. After running 900 miles at between 1250 and 1600 RPM I ran it up again to WOT and still no smoke.

At 1800 RPM, the turbo is just starting produce boost. The Cummins engine performance curve shows I should be generating about 150 HP at that point. Essentially the next 800 RPM gives me almost 270 HP. At 1800 RPM I am hitting about 9.0 knots or about .3 knots over hull speed. I guess you can look at loading two ways, before the turbo becomes effective and after. At 1250 RPM I am using a little less than 1/3 of the available HP before the turbo becomes effective but a little more than 1/10 of the available HP with the engine at WOT. Am I running 30% load or 10% load? Does the engine really care?

Tom
 
For heaven's sakes...all this overload, underload...what happened to the Wombling free bit, enjoying life out there..? All this talk is making everyone anal retentive OCDers..!

Just run your boat at its sweet spot, whatever that is...make sure she's up to normal temp, and enjoy..! In my case with trusty Lehman 120hp, 5000 hrs plus - don't know exactly because the hr meter died years ago - she come to 85-90ºC, ( I wish you guys would get up to speed with your units), and sits there at 1800rpm, and has done so all its life. I doubt it has had its neck wrung to WOT very often, certainly not by me, as I hardly ever do 4 hrs straight running at a time anyway, and she still runs sweetly and smokeless, and uses hardly any oil. So, what does that tell you..? Just stop worrying about it, ok..?
:nonono: :whistling: :D :flowers:
 
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Peter B said:
For heaven's sakes...all this overload, underload...what happened to the Wombling free bit, enjoying life out there..?
...
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An obscure reference that this Brit got!

And I happen to agree that we're well off into OCD territory here. But if this is everyone's biggest concern then they're in good shape!

Richard
 
Britannia said:
An obscure reference that this Brit got!

And I happen to agree that we're well off into OCD territory here. But if this is everyone's biggest concern then they're in good shape!

Richard
Click to expand...

I knew there'd be some... :thumb::D
 
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