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Old 03-26-2016, 09:50 AM   #141
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Mark,
Looked like 3000hrs ... didn't compute.
Only 300hrs?
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Old 03-26-2016, 09:51 AM   #142
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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!!!!
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Old 03-26-2016, 11:47 AM   #143
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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.
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Old 03-26-2016, 12:00 PM   #144
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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?
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Old 03-26-2016, 02:01 PM   #145
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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.
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Old 03-26-2016, 02:44 PM   #146
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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.
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Old 03-26-2016, 02:54 PM   #147
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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.
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Old 03-26-2016, 02:58 PM   #148
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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
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Old 03-26-2016, 03:01 PM   #149
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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.

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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.
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Old 03-26-2016, 05:01 PM   #150
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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.
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Old 03-26-2016, 05:25 PM   #151
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Going back to the original post about the article....


I have 2 different mechanical engineers with tons of practical diesel experience both agree (me too, but I am just a troublemaker) that one of the photos in the article is ether mislabeled or being used incorrectly to describe underloading. Now that alone doesn't mean a thing necessarily.


It is the photo of the Turbo wheel that implies it has something to do with underloading. I am getting the feeling and agreement that the photo is of the compressor side of the turbo and what is shown would not be symptomatic of underloading...just crap ingested from the engine room. So I did a bit of browsing about diesel turbo troubleshooting and it all seemed to agree.


So take it for what it is worth...just a raised eyebrow at one part of the article...but like some have slammed others with...if that pic was inaccurate...what else made it past the tech editors?


I also read on the Banks Engineering site (aftermarket stuff mostly for automotive diesels) that having to let a diesel wt turbo cool down after a hard run (especially with synthetic oil) is pretty much a myth. The FAQ was short enough to not explain in great detail...but made it sound like you would have to shut off the engine while coasting down from 100 to see coking anymore....
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Old 03-26-2016, 06:47 PM   #152
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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.
Ski,
Is'nt it quite likely that an underloaded engine w cool lube oil could accumilate varnish deposits in the ring grooves and thus be subject to stuck rings? Of course that would lead to low compression and plow-by. And on an old FL or similar running at a 30% load would not get the oil warm enough I'm thinking. There is no heat exchanger that heats the oil .. How does that compute?


Not supprising the DD's have a problem w underloading w the cool intake air for combustion sweeping through the crankcase greatly cooling the underside of the pistons. Stuck rings from underloading seems almost a given to me in these engines.

There's no lube oil in the combustion chamber on the DD's like a two stroke gas engine so ideally there would be no smoke at all. However the oil control ring (lower) on engines in general vary widely as to how much oil they leave on the cylinder walls to lube the piston and rings. New Jaguar owners used to complain about high oil consumption but they were just engineered to lubricate rather heavily assuming the engines would be subject to high output use. So new Jaguars and DD's may smoke some when brand new.
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Old 03-26-2016, 07:40 PM   #153
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It is the photo of the Turbo wheel that implies it has something to do with underloading. I am getting the feeling and agreement that the photo is of the compressor side of the turbo and what is shown would not be symptomatic of underloading...just crap ingested from the engine room. So I did a bit of browsing about diesel turbo troubleshooting and it all seemed to agree.
You mean the photo of the compressor side of a turbo to illustrate what he claims is the result of "wetstacking"?
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Old 03-26-2016, 08:15 PM   #154
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Ski,
Is'nt it quite likely that an underloaded engine w cool lube oil could accumilate varnish deposits in the ring grooves and thus be subject to stuck rings? Of course that would lead to low compression and plow-by. And on an old FL or similar running at a 30% load would not get the oil warm enough I'm thinking. There is no heat exchanger that heats the oil .. How does that compute?


Not supprising the DD's have a problem w underloading w the cool intake air for combustion sweeping through the crankcase greatly cooling the underside of the pistons. Stuck rings from underloading seems almost a given to me in these engines.

There's no lube oil in the combustion chamber on the DD's like a two stroke gas engine so ideally there would be no smoke at all. However the oil control ring (lower) on engines in general vary widely as to how much oil they leave on the cylinder walls to lube the piston and rings. New Jaguar owners used to complain about high oil consumption but they were just engineered to lubricate rather heavily assuming the engines would be subject to high output use. So new Jaguars and DD's may smoke some when brand new.
Combustion air for a DD does not contact the underside of the piston, only the top. The underside of the piston has lube oil supplied, either by jet or by a shaker type two piece piston. Oil temp is tightly controlled on these like the Cummins.

Diesels rarely smoke due to poor lube oil control by rings. What does get in usually burns with the fuel. Smoke is mostly unburnt fuel, blue/white or if short on air, black. Blue smoke due to oil burning is more a gasser thing.

Been around many DD's that ran at very light load, they have not had any problems related to that. Carboned up rings is more a problem on ones run hard, where the heat cokes the oil around the top ring. Not a problem when run easy, simply does not get hot enough.

Still don't like running DD's super easy given a choice, but the owners run them like they want to and I have not seen any suffer from it.
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Old 03-26-2016, 08:39 PM   #155
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I have put over 2000 hours on a Ford Lehman running at about 30% load and oil analysis still shows perfect.

The coolant and oil are up around 180 degrees (175-185) after most of my runs.
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Old 03-26-2016, 08:41 PM   #156
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The well known, and oft pointed out here protocol for DD's is to run them up to 80-90% of WOT for say 15 or 20 minutes after a day at low speeds. Ski knows authoritatively whereof he speaks, much better than the dockside urban legends or those who didn't follow the protocol.

I always get a kick out of the hearsay crowd averring the fragility of these 30, 40, 50+ year old motors.
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Old 03-26-2016, 08:42 PM   #157
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You mean the photo of the compressor side of a turbo to illustrate what he claims is the result of "wetstacking"?
Yes
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Old 03-26-2016, 11:25 PM   #158
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I have DD 8v92s in my sportfisher, twin turbo, air coolers removed, rated 550 hp. If ran slow for several hours they can get absolutely obnoxious (noxious?). I would think if ran continuously at low load it would probably cause serious problems in the long run. They tend to use some oil when ran slowly, very little when ran moderately. The cylinder temps get to low for good combustion, hazy exhaust is the result. I had 4/53 DDs in my trawler, rated 120 hp, no turbos, propped for 2500 rpm max. I never saw them smoke at all. They burned clean even after 24 hours at 6 knots and less. They could idle for hours and not smoke.
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Old 03-26-2016, 11:55 PM   #159
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8V92 TI, TA: Comp ratio 17:1
4-53N: Comp ratio 21:1. At least some, most, of them are.

21:1 is a really high CR for a direct inj diesel. It will burn anything you squirt in there.
Always wondered why they went that high of a CR, but dang it they do burn clean.
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Old 03-27-2016, 12:12 AM   #160
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So, I don't get this angst about not working a Diesel engine. Truck drivers often sit in truck stops 12 to 48 hours idling their engines just to have AC. In my own trucking company our engines almost always reached 1 million miles, sometimes more. And think of the cases when the same drivers idle their trucks in the winter for heat.
I've seen heavy equiptment, graders, cat, that maybe were used a few hours per week, run continuously from September to May.
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