Under loading.

[FF]

. "Am I running 30% load or 10% load? Does the engine really care? .

The load is defined by the power an engine might produce at That operating RPM.

We have all seen the HP/RPM graph of an engine and it climbs as the RPM is increased.

A "proper" load is one that uses a good percentage of the power available at THAT operating RPM.

Cruising at say 1600 the engine might be well loaded ,might not be,

but a comparison to WOT is not valid , as you are not operating at WOT .

The attempt to match engine load to the prop is best done with a CPP , or perhaps a 2 speed tranny.

For most recreational boaters it is meaningless.

A good 8000 hour diesel will suffer massive abuse and still operate for 4,000 hours.

At the norm of 200 hours underway a year , its a LOT of years!

 

[Ski in NC]

Dhays- That qsb should be happy down at low load for hull speed running. One advantage is that the common rail injection has full control of injection timing, rate and duration... which the computer tweaks for the best burn. Something the mechanical engines could only dream about controlling, hence their smoke. If an engine is not making smoke, it IS burning clean, and qsb's are super clean burning.

It's a very nice engine, worry not.

Also much quieter at low power than it's mechanical predecessor. Really quiet.

 

[Nomad Willy]

But Ski,
Clean burning is only a small part of the question.
I thought it was mostly about lube oil temp.

 

[Ski in NC]

Lube oil temp on a Cummins is controlled in a fairly tight band by a coolant to oil heat exchanger. Oil temp will be around coolant temp at light load, about 15-20F higher at heavy load. You don't have to worry too much about oil temp on these. Not the same cool oil issue you get with sea water oil coolers on Yanmar, Volvo, Lehman, etc.

 

[dhays]

Ski,

Thanks for the input. As a newbie, one of the things that was a bit confusing is that there is a big difference between the older engines and the newer common rail diesels. I have only begun to figure that all out.

 

[Nomad Willy]

Thanks Ski,
Tom and I brushed on that a bit ago.
I think he mentioned a "plate exchanger"?

Wouldn't that be fairly easy to put such a heat exchanger on an old engine?

 

[RT Firefly]

Greetings,
Mr. mb. "Wouldn't that be fairly easy to put such a heat exchanger on an old engine?" Why on earth would you want to go through the hassle of doing that when it has been more than amply demonstrated that "underloading" is a non-issue with the older engines or in ANY engine, for that matter?

Erroneous statements such as "You have to run at 75% load" for example are simple fear mongering with no factual basis what-so-ever. KISS.

 

[psneeld]

Greetings,
Mr. mb. "Wouldn't that be fairly easy to put such a heat exchanger on an old engine?" Why on earth would you want to go through the hassle of doing that when it has been more than amply demonstrated that "underloading" is a non-issue with the older engines or in ANY engine, for that matter?

Erroneous statements such as "You have to run at 75% load" for example are simple fear mongering with no factual basis what-so-ever. KISS.

...the ONLY reason I thought about switching the oil cooler to coolant is to make it last longer.

After 10,000 miles and 2000 hrs of perfect oil analysis on my severely underloaded engine (and as you said....hundreds of Lehman or similar testimonials of rampant underloading) the backyard or even professional guidance has little merit.

Even a top engineer giving background guidance here (which I posted) blasted the worries about oil temp and incorrect friction analysis that was brought up.

 

[koliver]

After years of reading here about underloading, I believe I am guilty. After 1500 hrs on my replacement engines, I had occasion to see inside the cylinders. My mechanic pointed out the total lack of any of the loudly claimed effects of underloading.
now I will relax about my habits and just enjoy the ride.

 

[psneeld]

"hundreds of Lehman or similar testimonials ....." now hundreds +1....

 

[Ski in NC]

Yea, hard to argue with the success of the Ford/Lehman. Underloaded or not, they just putt-putt along.

One problem with underloading and low oil temp is moisture building up in the oil- Fortunately this is easy to check. Just look in the oil fill hole in the rocker cover and look at rocker shaft and springs and such. If shiny grey oily metal, whatever you are doing is ok. If milky sludge or rust is there, then there is a problem.

Takes 20sec to check.

I don't like engines running with too cool of oil, but if experience shows no problems like on the Lehmans, then it must not be a problem!!!

 

[Nomad Willy]

Greetings,
Mr. mb. "Wouldn't that be fairly easy to put such a heat exchanger on an old engine?" Why on earth would you want to go through the hassle of doing that when it has been more than amply demonstrated that "underloading" is a non-issue with the older engines or in ANY engine, for that matter?

Erroneous statements such as "You have to run at 75% load" for example are simple fear mongering with no factual basis what-so-ever. KISS.

No fear mongering from me RT. Just say'in what I think .. as usual. I probably would'nt run 75%. Fifty to 60% is probably best IMO. But at least most of the time w most engines 30% seems ok. A few years ago I was shopping for another boat and most of them (pridictably) were over powered and I had planed on running them at 1500 - 1600rpm propperly propped. So I was ready to go the low load route myself. But if half the boats had engines that produced 7 knots at 50 - 60% load I would'nt look at the overpowered boats. But if that's all that is availible (over powered boats) I'd buy one and make do. However if the engine croaked I'd be shopping for a much smaller engine .. w a little lower gear.

So keep on trawlering and don't mind my ideas. Your "fear mongering" comment makes me think that you must be buy'in into think'in light loads are'nt ideal. The comment came from somewhere.

 

[RT Firefly]

Greetings,
Mr. mb. 139 posts based on an article that is suggesting, or at least is being interpreted by some members that "underloading" is always bad for every engine and will lead to a shortened life and increased maintenance unless one runs every engine up to 75% load as much as possible. If one cannot even determine what the 75% figure represents, how is one to run at such a level? RPM alone is no indicator evidently. How is that not fear mongering?

Thankfully those that actually KNOW diesel engines have demonstrated that the article is pretty much a canard...not that I needed convincing.

My worry about the loading on my engines is just below my concern as to their color-red (white would be easier to spot and trace oil leaks).

 

[kulas44]

You can realistically expect about 5000 hours at that rating. But you wont run it at that rating all the time so it will likely last longer. And, 300 cubic inches at 2.2 hp per is not 180

 

[kulas44]

I should pay attention to what page I'm on.

 

[Nomad Willy]

RT,
Cool your jets. This is a forum. That's where people express their opinions. You've heard mine several or more times and if you really have been tuned in you should know by now that if you are burning 40% of maximum fuel your engine burns at wot propped correctly you're at 40% load. It's just a percentage of fuel burned compared to what would be burned at max power. Oh .. and you get the wot burn from your engine manufacturer.

Lots and lots of people on here w lots of opinions to read and consider. Too bad you and a few others have turned this into a bandwagon and as a result opposing views are less likely to be posted. But don't worry about your engine just because someone says you should. What we all should do is read all we can and make up our minds about what is most likely right and do what's best in our opinions. I know what I'm doing .. I think it's close to right and feel comfortable in my place. But there's lots of opinions to choose from and the most important opinion is our own.

 

[markpierce]

My engine reaches maximum/operating temperature at 1400 RPM, that's about 30-percent load. That's my "slow cruise" (a most-efficient and maximum torque 5.7 knots) but I normally operate at 1800 RPM (45-percent load at 6.3 knots, a knot below hull-speed).



Hull speed is reached at 2200 RPM with a 72-percent load. Maximum engine speed is 2400 RPM, with little speed increase.

 

[Nomad Willy]

Perfect Mark,
Looks like you've got some time on the clock too.

 

[markpierce]

Perfect Mark,
Looks like you've got some time on the clock too.

Averaging about 120 hours a year.

 

[psneeld]

Greetings,
Mr. mb. 139 posts based on an article that is suggesting, or at least is being interpreted by some members that "underloading" is always bad for every engine and will lead to a shortened life and increased maintenance unless one runs every engine up to 75% load as much as possible. If one cannot even determine what the 75% figure represents, how is one to run at such a level? RPM alone is no indicator evidently. How is that not fear mongering?

Thankfully those that actually KNOW diesel engines have demonstrated that the article is pretty much a canard...not that I needed convincing.

My worry about the loading on my engines is just below my concern as to their color-red (white would be easier to spot and trace oil leaks).

...

While the article may contain valid points...those points like every post have to be put into perspective.

Those here with real experience , whether repairng or driving know that generalizing has its place but obviously has exceptions.

Suggesting that others worry about the way they are operation their engines without regard to what those particular engines can or can't tolerate is just that...possibly giving the idea that others could be hurting their engines unecessarily. Not what most members want to do.

I often find myself writing long posts only to delete them as while the point may be valid...without direct application to the OP.....all I am doing is generalizing or telling many what they either already know or don't care about. I still may do that sometimes and it bothers me so I do apologize for those slip ups...

 

[Nomad Willy]

Mark,
Looked like 3000hrs ... didn't compute.
Only 300hrs?

 

[Baker]

I often find myself writing long posts only to delete them as while the point may be valid...without direct application to the OP.....all I am doing is generalizing or telling many what they either already know or don't care about. I still may do that sometimes and it bothers me so I do apologize for those slip ups...

And for this, we applaud you!!!!! Nothing like droning on and on about stuff that has been droned on and on before.... That used to happen a lot on here. Doesn't seem to happen anymore. Thanks for your participation and adherence to this behavior!!!!

 

[Nomad Willy]

HaHa ..
So Baker you think we've droned on and on about underloading enough? Many do .. but many of the many keep posting ..... and now and then something new comes up. The only thing new is blow by blow accounts of someone buying a boat or fix-it threads. If it wasn't for rehashing the main subject threads There would'nt be much "beef" here.
But if the mods want to bann underloading talk I'm OK w it. After all we have said about 98% of what could possibly be said. One thing is odd and that's that people get tired of talking about a topic and urge that we move on and/or bring out the dead horse sometimes succeed in killing a thread .. but in a short time up comes the subject again and there they are talk'in it up again.

But if other members keep talk'in about it (whatever "it" is) and I have something to say .. I'll say it. And if it's not the most popular thing on the dock I'll probably still say it. Some like .. it some don't.

 

[BandB]

Generalizations may have their place, but it's not a very large place because they so often get one in trouble. It doesn't work for what anchor or what boat to get or what speed to run it or where to get your hair cut. We're all so different and our boats and engines and generators are. The way we use them is. We have engines that the base engine is used for continuous WOT use in very large commercial ships. However, our model, has much more horsepower and is designed for light boats and light loads. Even things which appear simple or complex. What do you use to wax your boat? Well, is your boat gelcoat, Awlgrip, Alexseal, Dupont, or what? They all specify very different care and Awlgrip specifies clearly "no waxing."

I try to qualify my answers but don't always do that well. However, I do attempt to say if something is true for a rather broad spectrum of boats by saying "many" or "most" or if it's true for only specific engines, say which engines. We have our only Yanmar engine in a RIB with a jet drive. Certainly far different than a Yanmar in a trawler with a propeller.

I think then for those who promote themselves as professional writers, and I'm not aiming this at the one who was here but at the group in general, the obligation to differentiate is even more important. Similarly the Tony Athen's of the world as well, making it clear that he's talking about his extensive experience with Cummins. We recently got our first Cummins product in the form of Onan Generators. I read and I listened to learn it's differences and exactly what the manufacturer recommended. My experiences to that point were with relatively small Kohler units and with larger Northern Lights.

We also have to be discerning listeners. Take all we hear with a grain of salt. Check it out with others. Most importantly go to those with the specific expertise and go to the manufacturer. Even in the manufacturer be sure it's the technical area. Recently I knew of an employee of a Generator manufacturer who gave a strong proclamation at the Miami Boat Show that was in complete conflict with what the manufacturer says.

Then we have to put it all in perspective.

We've talked about under loading to the point of exhaustion. But I want to ask one last very simple question. Has anyone here ever experienced a problem with an engine on their boat (no cars or airplanes allowed) that was attributed to or showed signs that under loading was a cause? If the answer is "no one" then I'd say it's not something for the TF group to obsess over. Be aware of it, but know the odds of it impacting you are minimal.

So, speak up if you've actually had a problem resulting from under loading. Not that you've seen it, or read about it, but experienced it. Don't all speak up at once. Do I see any hands raised?

 

[Mako]

So, speak up if you've actually had a problem resulting from under loading. Not that you've seen it, or read about it, but experienced it. Don't all speak up at once. Do I see any hands raised?

Back in my twenties when I had my first diesel, and old-time 6-71, I learned the hard way that DD's do not like to be underloaded. I admit that I had long run times at slow speeds. When I hired a mechanic to help me (or was I helping him???) replace the head (a two valve), he taught me about how the crankcase cools off at low speeds because of the blower.

The log showed that the previous owner ran at slow speeds also, and that engine always blew light smoke. Never cleared up in the years that I owned it.

So, not sure if that qualifies for what you are asking. So despite what 100+ posts in this thread state, after owning 3 of those beautiful 6-71 noise-makers in two boats, my own opinion is that under loading is a serious issue with them.

 

[BandB]

Back in my twenties when I had my first diesel, and old-time 6-71, I learned the hard way that DD's do not like to be underloaded. I admit that I had long run times at slow speeds. When I hired a mechanic to help me (or was I helping him???) replace the head (a two valve), he taught me about how the crankcase cools off at low speeds because of the blower.

The log showed that the previous owner ran at slow speeds also, and that engine always blew light smoke. Never cleared up in the years that I owned it.

So, not sure if that qualifies for what you are asking. So despite what 100+ posts in this thread state, after owning 3 of those beautiful 6-71 noise-makers in two boats, my own opinion is that under loading is a serious issue with them.

Actually it is what I wanted. Now, it's a specific engine and a long time ago, but it's a personal experience. You also stated a reasonable conclusion that based on your experience with three 6-71's your opinion is that under loading is a problem with them.

 

[koliver]

Not sure if light blue smoke from a 6-71 qualifies as evidence of underloading.
My own experience with the 6V71 that was in the fishing boat I worked on as a kid is that it always blew light blue smoke, and that engine started life as I started work on that boat, so no history of underloading whatsoever.
Isn't light smoke from a 2 cycle engine to be expected? Almost the same as older 2 cycle outboards, when compared with 4 cycle?
Isn't that in fact what led to the demise of the DD 2 cycles? Nothing to do with underloading.

 

[Mako]

I suppose the question that any owner should ask from his engine manufacturer, is what would be the minimum continuous loading for his specific engine to keep it happy and healthy without having to worry about occasional high power runs to clean it?

Personally for my next boat I am more concerned about the maximum continuous loading since my personal preference is that I do not want to own an engine that will be run below 50% for most of its life - that's a big waste of money if the huge reserve is generally never going to be needed. That's a different thread of course

 

[Mako]

Not sure if light blue smoke from a 6-71 qualifies as evidence of underloading.

I'd bet there are some DD mechanics on this Forum who can clarify that. I can't - am just stating my opinion.

Isn't light smoke from a 2 cycle engine to be expected? Almost the same as older 2 cycle outboards, when compared with 4 cycle?

I think you're referring to engines with an oil-gas mixture, like a mini-bike. They always blow smoke.

 

[Ski in NC]

Light blue out of a DD is usually either low compression or poor nozzle spray pattern. Neither are typically caused by running low load. Can't diagnose very well over the interweb, though.