Running a Diesel at Idle

[therondor]

Originally Posted by JK n Smitty

In a discussion on the sailboatowners.com forum, I had posted that it was bad to run a diesel at idle. I was quickly rebuked on this point by some knowledgeable/experienced boaters, including one very well respected moderator/featured contributor. I have also seen this subject come up on the Cruisersforum.com.

First thing, lets establish the definition of idling because this was of some issue. In the case of this discussion it would be running your motor in neutral. Even if you bring the RPMs up to 1,000 you are still idling your motor. For instance, the idling range for my Universal M25-XPB is 1,00-1,200 RPM.

From the Universal Diesel Operations Manual - February 2010

Now, I have always operated under the notion that idling is bad for your diesel engine. For instance, running your diesel at anchor to charge your batteries and heat hot water. My owner's manual tells me such:


But here are some quoted responses I got during the discussion on Sailboatowners.com.

From jviss:

For millions of sailboats running the main propulsion diesel is de rigueur for charging batteries, including everything from affordable, 20-something footers to 1/2 million dollar plus coastal cruisers (from Morris Yachts, for example). So while you may have a theoretical point, in practical terms it is meaningless. To paraphrase you: in general, it doesn't matter.
I don't idle mine, I usually run it at 1000 RPM or slightly higher. I don't get enough of a difference in output at higher RPMs to make it worth the extra noise. At idle (700 RPM) it doesn't make enough voltage to charge beyond a float level.

The only potential negative effects are glazing of the cylinder walls over time, that may cause some smoking. Mine has not exhibited this in 29 years of operation (at about 3000 hours). And, if it becomes necessary it is correctable: Westerbeke used to run generators on a dyno at 80% load with a teaspoon of feldspar in each cylinder to roughen up the cylinder walls and stop the smoking! (maybe they still do). You can break the glaze with a hone pretty quickly when it's time, like every 40 years or so. Probably won't even need new rings.

A big charging load, taking conversion efficiencies and drag into account is about 3 or 4 HP, which is about 15 to 20% of max rated output for this engine; so, hardly idling.

A bonus is that it heats the domestic water, too...

From Maine Sail:

My buddy Darren owns a good sized excavating, irrigation and landscaping company in Colorado and we talk diesels quite a bit. Just got to see him last week.. He has a good sized fleet of them and a couple of them have over 20k hours with no rebuilds. The last time I spoke with him about engine longevity he had one Yanmar block and one Mitsubishi block with over 20k hours. He bought both of these machines used with about 5k hours on them back in the late 90's.

Most of his smaller engines are either Yanmar or Kubota but he does have a few Mitsubishi's too. His engines run all day and never shut off and they idle for long, long, long hours. Now granted these are not in a marine application but in well over 500,000 hours of combined run time on his fleet he has yet to rebuild an single small diesel engine. All his machines run Shell Rotella and it gets changed regularly. Of course he buys his oil in 55 gal drums and I buy it by the gallon...

If heavy equipment running Yanmar, Mitsubishi and Kubota blocks can rack up10k to 20k hours, while doing hundreds and hundreds of hours of idling per year, with no rebuilds then a well maintained marine diesel should be able to do the same.

When we had the discussion about not letting diesels idle a few years ago he just laughed about the glazing the cylinder walls. His sarcastic comment was something like "Sh&t I better let my guys know not to let them idle". Course he'd already been doing it for 20 some odd years, with no failed engines or rebuilds needed, so he was surprised to find out his engines were going to die soon...

Our engine has idled perhaps half or more of its 3600+ hours. It burns ZERO oil, has cross hatching in the bores that looks like new and she purrs like a kitten. We have Sea Frost and often sail with the engine idling or will let it idle to chill the plate if we are alone and not disturbing others. Our boat also did a five year 24/7 on-the-hook almost circumnavigation. She had no generator and only the factory alt and a single solar panel. The batteries lasted six years and were still kicking.

When this came up on the Cruisersforum.com, the following replies were posted:
From Jd1:

Everything I have read and have experienced supports the notion that a diesel is best run in the 75% to 90% (or thereabouts) power output range. An occasional period of idling will not be detrimental if followed by a period of running at a good load (for example starting the engine and letting it idle for a while to warm up before heading out). The frequent in and out of the harbour short hops are murder to the poor diesel.

I can not explain why automotive diesels, which spend a lot of time idling, survive. I could speculate though that they would last a lot longer if run like a semi trailer road transport truck - much harder and much longer.

A modern diesel should last 20000 to 30000 hours yet they get replaced in boats at a fraction of the expected service life. IMHO that is, amongst other things, related to the unfavourable working conditions of a sail boat auxiliary engine.
Diesels like to run fairly hot (180 - 190 F range). Running colder and/or idling a lot causes more wear and tear, carbon buildup and soot buildup.

I am sorry that I can't produce a link to something official looking.

From nes:

I don't know if this applies to the small diesels (non turbo/super charged), but the diesel generator that I have a lot of experience running had 36 cylinders displacing 645 cubic inches each, and it had an interesting gear driven (at low load) turbo (at full load) charger/compressor.

This diesel had very specific directions against running at low load (less than 30%).

The reason given for the load restriction was lower cylinder pressure at low load. The piston rings are designed to operate at rated load combustion pressures, this ensures normal lube oil consumption rates. Light and no load operation promotes “souping”, which is excessive oil escaping past piston rings into combustion chamber. Souping causes smoking exhaust and potential exhaust manifold fires.

The recovery direction, if the engine was run at low load, was to follow that with at least a half hour at greater than 50% load.

Based on what I have seen running this engine, I would suggest that it is not a good idea to do extended runs at low load.

[Interesting side note, jviss and Jd1 both have Catalina 36s.]

So by posting this (and cross posting it to several different areas) I am hoping to get some feed back that will help me determine if idling is bad for my diesel. If you comment on this, please try to provide something to support your opinion.

Fair winds,

Jesse

Cross posted on Sailboatowners.com and my blog.

smitty if you read the book it states that idleing for long hours to break in the motor is a bad idea.

[deckofficer]

What Bobconnie said is the way to approach proper charging with pulley ratios. Determine from the OEM the max rpm rating for the alternator and compute a pulley ratio to give that rpm at the engine's max rpm.

Let's say the alternator has a 6000 rpm design limit and your diesel's max is 3000 rpm, the alternator pulley would be 2" if the engine pulley is 4".

[rebel heart]

Originally Posted by Surrymark

From my diesel class with Jon Bardo at WoodenBoat:
• Sure, idling is not the best, but everybody does it.
• A diesel not under load is idling, no matter what the rpms.
• A battery won't charge any faster than the rate at which it discharged.
My takeaway is to run the engine at low rpms in reverse, when I am sure that the mooring or anchor will hold.

Even cursory usage of charging systems disproves this assertion.

Just operating the in the bulk absorption zone, you can suck out 24 amp hours in a day with 1 amp constant draw, and an 80 alternator can put that back in what, 15 minutes, if that?

[hellosailor]

I suppose only a trucker could tell you why he leaves his engine idling all the time, but I was taught by a combustion engineer, a PhD twice over, who designed parts that he receives patent license fees from, on some 90% of the diesel locomotives on this planet, why he thinks they do it.

Starting and stopping a truck engine, or any engine, places impulse and load shocks on the bearings and to some extent on all the moving parts. Startups create undue wear because there is zero oil pressure and even the finest shafts literally slam around in the bearings until there is oil pressure to cushion them. Starters and alternators throw spikes into the electrical system, and starters take wear every time they engage and disengage.

The bottom line, as he put it, is that fuel is the cheapest part of any engine, and that letting the engine run costs much less in the long run, than replacing all the things that are damaged by every routine startup and shutdown.

Glazing the cylinder walls or coking the exhaust by idling a diesel engine? Negligible compared to the costs of letting it idle. If you're a long-haul trucker (or a locomotive engineer) and you can't restart your engine, for whatever reason, now your entire load may have to be dumped, especially if it is perishable. So you burn the fuel, because that way you KNOW that all you have to do it put it back in gear when you want to leave.

Very different set of priorities compared to running a small boat engine to charge the batteries.

Feldspar sounds like a very clever way to clean cylinder walls. IIRC that's the abrasive in BonAmi cleaner, chosen as a soft safe abrasive, very similar to the diatomaceous earth ("fuller's earth") used in traditional white tooth pastes. Shoot a little Crest into the intake every thousand hours, huh?

[sardinebreath]

Originally Posted by sailorboy1

I bet there are 2 main things that wear out engines: 1 - running them, 2 - not running them

Not running them doesn't really wear them out; it just seems to ruin them. When I drove semi I was instructed by the owner to keep the engine running until it was going to be parked for days. Sleeping, eating, whatever--the engine ran until I got to the other coast. And he was paying fuel and maintenance.
Probably the greatest wear on any engine, diesel or gas, comes on startup. The colder the engine, the more damage done. (Pre-start engine heating would likely add years of life to an engine). Some diesel mechanics feel that an engine has some set number of startups in them: if you never turn them off, they'll pretty much run forever (is the thought). I never heard a word about avoiding idling and would often idle for 6 or 7 hours straight. But the engine was always run hard again afterwards.
I actually don't feel like I know that much about diesels though. Just passing on things I've been told over the years.

[eyschulman]

I don't get it why are there so many people who think idling has much to do with marine diesel life. It is the salt water and salt moisture(marine environment) and the load factors,particularly overloading in marine drive(much different than a road loading) along with overheating poor exhaust geometry and poor maintenance that kills marine motors. This is not to say that low load idling is good for a marine diesel but is probably after a proper break inn and regular intermittent high load use of little or no significance. Read the appropriate(several) articles on boatdiesel.com or Tony's tips at Seaboard marine site if you need further information and education regarding this issue.

[hellosailor]

"Some diesel mechanics feel that an engine has some set number of startups in them:"
And they do. As the PhD explained it, when you star an engine with no oil pressure, the shaft bangs at least three times against the bearings (moving in a triangular fashion not purely rotary yet) with no lubrication and a lot of side load (the banging). So literally you can say the bearings are good for xxx,xxx number of slams before they get distorted and wear out, and every time you start, you decrement the number of slams left before bearing failure.
Which is one reason that oil sampling programs will tell you how much bearing metal is in the oil. As they get worn more, more bearing metal is ground off into the oil, and at a certain point the oil analysis will tell you "bearing failure to come" and you overhaul the engine before that fails, while it is still "perfectly good".

IIRC there's an old Sinatra movie (might be The Devil At 4 O'clock) where he pilots a Grumman Goose, a small twin engine seaplane in the south pacific. During one of the takeoffs they call for the OIL PRESSURE PUMP to be turned on. That's right, when your engine is critical, you have an electric pump that builds oil pressure BEFORE you start the engine. Of course electric oil pressure pumps mean more stuff to fail, which is why we don't have them on cars and boats. Usually.
And synthetic oils are designed for radically better "thin film performance" than dino oils. They will cling to bare metal many hours longer than old oils did, so if you are using synthetic oil, and you restart after an hour, the bearings are no longer bare metal, there is still an oil film clinging on them, reducing some of that startup damage.
As Robert Heinlein said, any sufficiently advanced technology is indistinguishable from magic. You can't tell any of this stuff simply from owning and operating one.

[FlyingCloud1937]

WOW...still going just like the bunny

Originally Posted by FlyingCloud1937

Assuming a properly broke-in diesel engine, it is still harmful to run at idle.

But to define idle, is what needs to be done. A diesel that is started and left to idle without any load will do a couple of things that are very bad. One all injector pumps and injectors are designed to govern fuel at rated loads.

They are very inefficient at low speed/idle. In that they inject more fuel at each compression stroke then they can efficiently burn. This leads to higher nox and carbon deposits, it also washes the cylinders, which results in gums and varnish and leads to diesel contaminated oil.

Along with that the acids created by the unburnt fuel are harmful to all the bearing and other friction surfaces. As well as creating moisture in the oil. Along with this additional inefficiencies of the pump/injectors at low speeds is the flame spread during the combustion cycle which helps exacerbate the rich running.

To confirm this all you need do is look at the HP/Torque curve of your engine, and then compare it to the fuel burn/efficiency curve. The work done per gram of fuel increase as the speed/load and work done increases.

So we can all agree that an idling diesel engine is not good for long term health. Just because some trucker does it doesn't mean it's good for the engine. Nor is running an engine lightly loaded at any speed, this is exactly why truckers have 18 gears. Not to mention that almost every country/state has anti idling laws, which are enforced.

Now we can run an engine at low speeds as long as we have a load on the engine, and it's not really idling. It's actually doing work. So go back to your HP curves and note the HP produced at the various speeds, and try to match loads/work being done. This will help, as it will cause the exhaust gas temperature rise above 300F, this means that the cylinder temp is high enough that it's burning more efficiently, then at idle which is usually below 270F. Any EGT below 300F means it's wet stacking/running rich and is bad for the engine. Ideally a diesel should be running higher then 550F, and max efficient burn is in the 700-900 EGT depending on the engine.

Constant speed governors such as for a generator, operate differently then a variable speed governor, even if the two engines are the same. They are tuned to provide the best results for which they were designed to run.

This is easily confirmed by noting that an engine rated by the EPA to run at constant speed won't meet EPA for a variable speed, and vise-verse. And if that is not enough just give your local injector pump rebuild shop a call and ask them if you can replace one pump for another.

Hope this will get the topic/discussion going in the right direction.

Lloyd

[Dockhead]

Originally Posted by hellosailor

"Some diesel mechanics feel that an engine has some set number of startups in them:"
And they do. As the PhD explained it, when you star an engine with no oil pressure, the shaft bangs at least three times against the bearings (moving in a triangular fashion not purely rotary yet) with no lubrication and a lot of side load (the banging). So literally you can say the bearings are good for xxx,xxx number of slams before they get distorted and wear out, and every time you start, you decrement the number of slams left before bearing failure.
Which is one reason that oil sampling programs will tell you how much bearing metal is in the oil. As they get worn more, more bearing metal is ground off into the oil, and at a certain point the oil analysis will tell you "bearing failure to come" and you overhaul the engine before that fails, while it is still "perfectly good".

IIRC there's an old Sinatra movie (might be The Devil At 4 O'clock) where he pilots a Grumman Goose, a small twin engine seaplane in the south pacific. During one of the takeoffs they call for the OIL PRESSURE PUMP to be turned on. That's right, when your engine is critical, you have an electric pump that builds oil pressure BEFORE you start the engine. Of course electric oil pressure pumps mean more stuff to fail, which is why we don't have them on cars and boats. Usually.
And synthetic oils are designed for radically better "thin film performance" than dino oils. They will cling to bare metal many hours longer than old oils did, so if you are using synthetic oil, and you restart after an hour, the bearings are no longer bare metal, there is still an oil film clinging on them, reducing some of that startup damage.
As Robert Heinlein said, any sufficiently advanced technology is indistinguishable from magic. You can't tell any of this stuff simply from owning and operating one.

Engine pre-lubrication is not complicated or expensive. Here's one aftermarket system: Engine Pre Lube - Pre Lubrication Starter System for Engines -Preluber

You don't need an electric pump; just a solenoid valve and little pressure tank. I've seen prelube system on boats from time to time (for some reason, they seem to have been fairly common on Detroit Diesel 2-strokes), and years ago, I had a race car with a pre-lube system (I think it was called Accusump or something like that).

If it really made such a big difference, I believe we would see more people using them. I think rather few small marine engines are kept long enough to need main bearing replacement.

[transmitterdan]

My Yanmar manual recommends starting after several days storage by holding the stop control and cranking for some seconds to let the oil pump start first. Then release the stop control and the engine starts almost instantly. It sounds like a good idea and doesn't cost much.

I am amazed at the posts about truckers idling. This just is not done these days. Fuel is a significant portion of total operating expense and the practice is illegal nearly everywhere there is enforcement of environmental regulations.

[svlamorocha]

Originally Posted by hellosailor

I suppose only a trucker could tell you why he leaves his engine idling all the time,?

This has been studied to death in large fleets of large trucks. Answers are: 1) to run the air conditioner/heater in trucks that do not have APU/genset/diesel heater 2) to tell the boss or customer (via hour meter) you are working when you are not 3) ignorance about cost-benefit analysis of this issue 4) driver does not care about fuel wasted/engine wear because he does not pay for it

When you install a GPS dispatch system one of the things you pick up is idling time that you did not know of (as when the driver stops on the way but does not turn engine off to keep the counter going).

I have done lots of performance improvement work in fleets of large trucks and in every case the experts who have done the numbers agree that idling more than a few minutes only makes sense if it is the only way to keep the operator from freezing to death or dying of heat exhaustion. Ask Caterpillar or Komatsu if you do not believe me.

+1 on the post that states that idling for more than X minutes is illegal in many first world locations.

C

[s/v Jedi]

Originally Posted by transmitterdan

My Yanmar manual recommends starting after several days storage by holding the stop control and cranking for some seconds to let the oil pump start first. Then release the stop control and the engine starts almost instantly. It sounds like a good idea and doesn't cost much.

I am amazed at the posts about truckers idling. This just is not done these days. Fuel is a significant portion of total operating expense and the practice is illegal nearly everywhere there is enforcement of environmental regulations.

Exactly what I do too (pushing stop button while cranking).

Modern semi's auto shutdown when left idling so all the facts posted here must be of old times

[Dockhead]

Originally Posted by s/v Jedi

Exactly what I do too (pushing stop button while cranking).

Interesting, Nick - what Yanmar do you have? I tried this with my 4JH3HTE and it tripped breakers. Would love to be able to do this at least after an oil change.

[s/v Jedi]

Originally Posted by Dockhead

Interesting, Nick - what Yanmar do you have? I tried this with my 4JH3HTE and it tripped breakers. Would love to be able to do this at least after an oil change.

4LH-HTE. Love it.

[tropicalescape]

Originally Posted by transmitterdan

Several people in this thread have said truckers idle their diesels a lot. In the US and many other countries this is not true these days. Idling while parked is illegal in most states in the US. I believe it is the same in many EU countries too. It's not because states are worried about the engines. It's about pollution control.

Your right,its been quite a while since ive been to a truckstop and seen this..