Under loading.

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....

Ski in NC said:

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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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.

psneeld said:

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.

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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"?

manyboats said:

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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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.

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.

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.

BandB said:

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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Yes

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.

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.

Gordon J said:

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.

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I've seen heavy equiptment, graders, cat, that maybe were used a few hours per week, run continuously from September to May.

"I had my first diesel, and old-time 6-71,
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"

If it was old enough ,,WWII to late 1950's it probably had H style injectors , not the more "modern" N style.

These always smoked a bit from idle to red line .

No cause for alarm .

This is beginning to rival an anchor thread. We've yet to hear from an actual M/V owner whose propulsion engine was all glazed up due to chronic under loading. Would this seemingly rare and unique individual please come forth and state your sad story?

Some good has come from discussion of Steve's article - prop right, maintain properly, insure engine temperatures are in the desired range, monitor smoking and run the RPMs up from time to time to assess health. Just like the doctor said ---.

Ski,
OK good .. the blower on a DD blows the air into a chamber that sourrounds the cylinders .. separate from the crankcase. My two stroke MC past led me astray. So it seems just the turbo DD's have a low speed problem .. interesting.

Tom,
Your first paragraph sounds like a witch hunt but some things need repeating.

Tom I like your second paragraph. What is the desired range for lube oil temps? I remember hearing 180F a lot and I think 160. Is 160 high enough to prevent varnish buildup in the rings? This I would think would be a call for the oil people and specifically not the engine people unless they are passing on info from oil people. The range would probably be specific to oil grades. But the engine people would need to give out information that would fly for most all lube oils. Or perhaps listing a specific grade would cover their tails. I wonder how much the oils would vary in their temp requirements?

I ran a small yard , back when 4-107 and Volvo MD 2 or 3 were common for sail propulsion 25 -35 hp or so..

The few folks that headed south every winter replaced their engines far later than the usual summer sailor.

These good folks would take the LIRR and a bus to get to the boat yard,
They would row out and start the engine to make electric for a DC refrigeration unit.

They would row ashore , have dinner and visit the grocery and bring out the provisions for the weekend.After 4 or 5 hours of ideling the converted ice box would be cool enough to go till the next day.

Most of these were far smaller than a propulsion engine in a modern "trawler" .

They didn't die from overwork!

Those that wish to understand underloading should contact National Fisherman , they had a great 2 part article about 15 years ago.

Usually 600HP ish engine running refrigeration or hyd at night using 40-50HP for hours on end.

FF I love the comments about the "good folks" .. taking the buss and the LIRR (some kind of train?) and then rowing out sounds like something we all should do for a season for ..... scope.

That's what Willy had when we bought her .. a 4-107. Was hard starting and old. No glow plugs. Didn't see that as a good thing in Alaska so we repowered. Willard installed an engine giving 36hp and we repowered w a 37hp engine. Took me quite awhile to conclude Willard got it right unlike most all others re the amount of power installed. Later they did the over power too.

manyboats said:

HaHa ..
So Baker you think we've droned on and on about underloading enough?

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Actually I don't. I think this has been a good thread with a lot of good information. And it does add some understanding to an age old "myth"...for lack of a better word. For those running the old Lehmans and Perkins type of engines, I really don't think they are running them underloaded. I would say the vast majority of folks likely run them around 1800RPMs. And that is a good enough load. I personally don't have to worry as I run my engines at about 70%(ish) of power. Probably less since I am fairly underpropped. I have no soot and pretty much no smoke of any kind once the engines are warmed up. They smoke like crazy on start up in the cold but run as clean as anything I have seen while warmed up.

Two big thumbs up John!

"FF I love the comments about the "good folks" .. taking the buss and the LIRR (some kind of train?)"

Customers are always good folks. Many New York folks do not have an auto.

Just off street parking can be $200-$300+ per month , inside even more,
so most will use publik transportation like the underground electric sewer , or rent a car as needed.

LIRR = Long Island Rail Road.

FF,
Known many Juneau people that didn't have cars either.
Walkers and cabs. Very steep hills too.

DHays, 3 pencil zincs for that engine, cheap! Might need to shorten generic zinc, that goes into heat exchanger about 1/4 inch.

Rebel112r said:

DHays, 3 pencil zincs for that engine, cheap! Might need to shorten generic zinc, that goes into heat exchanger about 1/4 inch.

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Thanks Rebel. Survey is Wednesday.