Light Loading of Diesels -- How Harmful?

[a64pilot]

Originally Posted by Guy

Well I know that you know that a turbine reaches it's highest temp during a start. Not much need to warm it up after that.

Some do, some actually start pretty cool, but that is gas temp, not metal temp or oil temp. It takes a little while for the oil to warm and the turbines themselves to get up to temp. The cool down is more of a helicopter thing, airplanes are a little like boats, they go to low power on approach and stay at low power util parking, so they are cooled down already, helicopters pull lots of power to hover so they are at high power until landing (wheeled helicopters being the outliers).
New GE H-80 engine requires a 5 min warm up as per GE and I wrote into the operators manual on the aircraft a two min cool down as I believe that will extend it's life.

I figure if you warm it up slowly and it doesn't really need that, you have hurt nothing. It may be an old wives tale coming from 60 weight oil used in the radial engine of old, but I still do it.
There are millions of automobiles started and driven off every day without a warm up and live long lives anyway

[GrahamHO]

The smoke may be from oil accumulating in the turbine at idle. Probably not a bad thing apart for using a little oil. Trucks, busses, and couriers all leave their engines idling rather than shutting down. Even gas turbine choppers often leave their engines idling as they log the number of engine starts for maintenance. Your alternator can easily absorb 1, or 2 HP which is providing a load. There are about 746 watts to one HP so you can calculate that. Dedicated diesel generators probably run higher than 1200 rpm. Personally I run my smaller non turbo Yanmar around 1800 rpm for battery charging if necessary.

[GrahamHO]

By the way; black smoke is fuel, white smoke is oil.

[a64pilot]

Oil is usually blue
unburned fuel can be a white vapor, look at the stack of a cold Diesel as it tries to start.
Burt fuel, but not enough air is black, an extreme example is watch a tractor pull
White can be steam too, usually both fuel vapor and steam dissipate rather quickly, smoke doesn't.

[deblen]

This recent thread may apply to UK fuel:

http://www.cruisersforum.com/forums/...da-155241.html

Cheers/ Len

[Compass790]

Every diesel manual I've ever read says not to run at idle with no load for long periods of time. Most of the mobile welders with diesel engines had a large label on the side saying the same thing. Guess the manufacturers think it's a bad idea then. Clogs the exhaust if you have a raw water cooled engine for a start.

[sailon46]

Originally Posted by Dockhead

I ran my main engine for about 40 minutes during the weekend with no load other than my newly fixed alternator (pulling a few horsepower), at a high idle speed of about 1200 RPM.

Before shutting it down, I ran it up under load (as the manual says to do), and was amazed that it emitted billows and billows of thick smoke. This doesn't seem good at all -- wet stacking?

My Yanmar 4JH3HTE is very smoky anyway. Has always been. I almost didn't accept the boat because of the smoke. Finally did, after a crack surveyor told me that the engine was in good condition and that this smokiness is sometimes characteristic of Yanmars. Meanwhile I had made the sellers send in injection pump, turbo, etc. for overhaul. I have since even changed the injectors, but nothing ever changed -- in more than 1500 hours since then, the engine has run perfectly, starts instantly, and -- smokes. It's the best starting diesel engine I've ever encountered -- even in below freezing weather, it starts in apparently less than a revolution. I've never used the air preheater. That's supposed to be proof of good compression.


But these billows were far beyond the usual smoking. It cleared up after a few minutes of running hard under load.

So, WTF?

I guess there just can't be any doubt that these engines don't like being run like this.

However, the U.S. military did a very extensive study, and claim that wet stacking, while annoying, is not actually harmful:

http://www.dtic.mil/dtic/tr/fulltext/u2/a151273.pdf


Any comments? I don't really know what to think.

Dock head dying I have the same engine on a 52 beneteau in the carribean same ongoing problem billows of white smoke. I started thinking bad things about the engine till one day the engine stopped and couldn't press down the manual pump of the secondary filter. Had bought diesel in Grenada port Louis yacht club an guadeloupe point a pitre marina. Anyway cleaned the primary full of nasal like excretions didn't fix it. But when I put anew secondary filter gone the smoke and I'm back with 3400 rpm no load and 3000 full load not maxed out
Hope this helps
Ernie

[GrahamHO]

Originally Posted by a64pilot

Oil is usually blue
unburned fuel can be a white vapor, look at the stack of a cold Diesel as it tries to start.
Burt fuel, but not enough air is black, an extreme example is watch a tractor pull
White can be steam too, usually both fuel vapor and steam dissipate rather quickly, smoke doesn't.

Yes that is more precise. Just that the color of the "smoke" is an indication.

[model 10]

Originally Posted by a64pilot

.
New GE H-80 engine requires a 5 min warm up as per GE and I wrote into the operators manual on the aircraft a two min cool down as I believe that will extend it's life.
e

Don't use that engine in any emergency craft, that's bs. If it's blowing you should be going. I don't want to be laying beside the road bleeding to death while you warm that stupid thing up.

[Sardean]

Hi Dockhead, sorry to hear you had to spend money on intercoolers with no improvement. I have seen a head clog up with carbon on a cherrypicker truck that gave simillar problem to you to the extent that the engine gave symtoms of needing a rebuild. The mechanic put a decoking chemical through the intake, this caused lots of smoke but then engine ran like new. Might be worth a try

Sent from my D6653 using Cruisers Sailing Forum mobile app

[TheThunderbird]

Originally Posted by CarlF

I often worry about light loading. Over the years I've picked up several bits of advice that I now practice but don't know if any of it is urban legend. Should I stop any of these?

- On starting cold (Yanmar with turbo) after a minute to be sure oil pressure is completely distributed, I will run at 1200rpm for a few minutes and then 1400-1600 rpm until the water temperature gets to at least 160 degrees (less than 10 minutes). I'll then reduce RPM but keep the temp above 160.

- Every six-eight hours of operation I will run under load for 15 minutes at 90%+ RPM

- When shutting down after a long slow speed run into the dock, I advance the throttles to the stops in neutral three quick times then wait 60 seconds at idle before shutdown. (This was recommended by a Mack Boring expert)

I get virtually no smoke.

excellent tips!!!

1) NEVER run a diesel engine idle, mostly so when cold (poor lubrication) since, by geometric design, strains on moving parts are HIGHER then at full rpm. it is due to inertial forces, which matter more than centrifugal ones, and which are less balanced .

2) modern diesel engines are turbo charged, and they consume more oil if run at low temp and/or low rpm... thus smoking, and possibly damaging the turbine!

2a) VOLVO recommends ideal T of 85Celsius on my TAMD-31 (1997)

3) if you like to run a diesel at idle rpm, better buy a heavy duty engine of 20HP/litre, running idle at 500rpm and 1200rpm full throttle!

btw, when running idle i DOUBT that your alternator may actually charge 100%.. have you tried with amperometer to test for it ??

finally, I hate to charge GEL/AGM battery banks by the alternator, as I CAN NOT CONTROL VOLTAGE OUTPUT, which can be so detrimental to battery life!! it is best for Acid Lead batteries, those used for the engine start only

[HappyMdRSailor]

Originally Posted by a64pilot

Hey, at least we know they are after coolers and not intercoolers That says a lot

Sent from my iPad using Cruisers Sailing Forum

Do they make fronter-coolers?

Originally Posted by Pauls

I bet you had a lot of fun with your 930. Sweet cars.

Indeed... But honestly I think the looks were the main attraction... As DH mentions later, better performers abounded... BTW... I used to service a Guards red 930... License plate = MOMSROD

Originally Posted by darylat8750

I seem to agree with a65pilot all the time. I will add here that there needs to be some load or higher than idle rpm for the turbo to add manifold pressure and without added pressure the intake air temp is not heated.

Me too... He's just a smidge smarter than the 'ol 64...

Originally Posted by Guy

Don't use that engine in any emergency craft, that's bs. If it's blowing you should be going. I don't want to be laying beside the road bleeding to death while you warm that stupid thing up.

I'm sayin !

[Dockhead]

Originally Posted by TheThunderbird

excellent tips!!!

1) NEVER run a diesel engine idle, mostly so when cold (poor lubrication) since, by geometric design, strains on moving parts are HIGHER then at full rpm. it is due to inertial forces, which matter more than centrifugal ones, and which are less balanced .

2) modern diesel engines are turbo charged, and they consume more oil if run at low temp and/or low rpm... thus smoking, and possibly damaging the turbine!

2a) VOLVO recommends ideal T of 85Celsius on my TAMD-31 (1997)

3) if you like to run a diesel at idle rpm, better buy a heavy duty engine of 20HP/litre, running idle at 500rpm and 1200rpm full throttle!

btw, when running idle i DOUBT that your alternator may actually charge 100%.. have you tried with amperometer to test for it ??

finally, I hate to charge GEL/AGM battery banks by the alternator, as I CAN NOT CONTROL VOLTAGE OUTPUT, which can be so detrimental to battery life!! it is best for Acid Lead batteries, those used for the engine start only

Thanks. All good advice which I've taken on board.

My alternator (Leece Neville school bus type) puts out quite a lot of power at low RPM. At 1200 RPM, I saw 70 amps and more at times (@24 volts; that's like 140 amps at 12). This is a good thing, since you do need power from the alternator at idle speed for working the windlass and, sometimes, the bow thruster.

As to charge control -- I have an Adverc external regulator for the Leece Neville. One of the very first things I installed when I first bought the boat. You can set it for gel batts if you want. It has an unusual approach to charging -- it hits the batts with 28.5 volts for 5 minutes, then reduces voltage to 27.5 for 15 minutes, then repeat. After a certain number of cycles, it lets the batts rest for a while, then starts over.

Adverc claim that this allows the batts to take more voltage, above the gassing voltage, but cycles back before they overheat. It seems to work very well, as even a fairly short run of motoring seems to leave the batteries very well charged.

[Dockhead]

Originally Posted by Sardean

Hi Dockhead, sorry to hear you had to spend money on intercoolers with no improvement. I have seen a head clog up with carbon on a cherrypicker truck that gave simillar problem to you to the extent that the engine gave symtoms of needing a rebuild. The mechanic put a decoking chemical through the intake, this caused lots of smoke but then engine ran like new. Might be worth a try

Sent from my D6653 using Cruisers Sailing Forum mobile app

"Decoking chemical"? I've never heard of that. Do you have any details?

[Dockhead]

Originally Posted by deblen

This recent thread may apply to UK fuel:

http://www.cruisersforum.com/forums/...da-155241.html

Cheers/ Len

Yes, I've noticed some differences in smoking, using different fuels. I bought a load of sweet, high cetane diesel fuel in Russia (I had it brought up by truck from St. Petersburg!) last year. It was diesel fuel, but different -- sweet smelling, and lighter and clearer in color, almost white. Running on this fuel, my engine smoked much less than it does with other fuel. Also ran noticeably smoother. This surprised me.

But other boats also running our heavy UK fuel, don't smoke like mine does, so I don't think this is the main problem.