Running a Diesel at Idle

[JK_Boston_Catalina310]

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 Cruiserforum.com (http://www.cruisersforum.com/forums/f54/running-a-diesel-at-idle-112105.html) and my blog.

 

[RichH]

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.

Standard industrial practice with steady state 'prime movers' (engines that operate at near constant load and constant rpm ... includes small boat engines) for maximum service life between either replacement or rebuild is to run the engine at 75% WOT rpm under 'normal' loading.

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.

The case for not running 'extensively' at idle rpm is valid; however in the case of boat engines its not realistically possible. The remedy is to get back to 75% rpm when possible .... in essence the goal is to *run the hell out of the engine* periodically to minimize cylinder glaze.
(Im not going to tell you that severely glazed engines can be remedied by dumping or injecting a mixture water and 'cleanser' into the air intake to scuff the cylinder walls, I'm not going to do that).

A *more important* issue for marine engines is operating temperature, the 'hotter' (steady state @ 180°F) the engine is operated the better the formation of protective 'black rust' (ferrous oxide) in the internal cooling passages of block, head and exhaust manifold. Long term idle speed running does not necessarily keep the cast iron component engine at this 'ferrous oxide' formation temperature and LONG term idle and LONG term 'shut down' will return that 'black rust' to destructive 'red rust' (ferric oxide).
Never 'store' or long term shutdown a cast iron engine by draining the cooling circuit; rather, add antifreeze with suitable 'anti-corrosion' compounds ... to keep the 'black rust' intact; 'draining/drying' quickly changes the black rust to destructive 'red' rust.
The issue of 'construction equipment' and 'truck' engines is very different, as their cooling circuits are 'closed loop'; and, any oxygen in the closed loop cooling system water is rapidly depleted. In contrast, marine engines are constantly fed 'oxygen enriched' raw water; thus, the high propensity to form 'red rust' in the raw water circuits.

Marine engines typically dont wear out, at least not at less than 8000 to 10000 engine hours .... they ROT OUT from the inside out. Rx (w/r to internal corrosion): run the hell out of the engine at FULL operating temps. and at 75% (WOT) rpm for long periods ... as much as possible.
Dont 'BABY' a marine engine.

 

[Maine Sail]

Jesse,

I am assuming your engine is already broken in? This removes that from the equation. Second if run at a normal 70% - 80% load often, and idling in-between to charge batteries, I've simply not seen bore glazing be a real or quantifiable issue, at least in my customer base.

Can it technically happen? Absolutely. I think we tend to miss that when charging, the engines are loaded pretty well, at that specific HP, so we are not just "idling with no load". While the load may be small and the engine may not warm up to operating temp in cooler waters if you then go our and run her hard after this you should be fine four thousands of hours. We are already at "thousands of hours" so know this to be true for our engine based on our real world results. I have zero issue running our engine at idle when needed and when it does not disturb or impact others.

Do I believe bore glazing can happen? Sure, but I see engines die far more often from lack of use or other maintenance issues rather than the cruiser who idles to charge and runs her hard when not charging..

It is also advised by almost all diesel generator manufacturer that they be "loaded" to approx 70-80% when run, and in the real world, that also rarely happens.

I have one customer with 6k hours on an old 8kW diesel Westerbeke generator. It has an old 50A Heart Interface battery charger that is the primary use for the gen set. They occasionally load it for hot water or the microwave but usually the 8kW generator runs powering a small 50A battery charger. Even with every load on their boat drawing constantly it can't even come close to the 8kW or even 6.4kW which would be the 80% recommended by the manufacturer. They have been lucky to load this gen at 30% and yet it has 6k hours on it and still runs just fine.

There are also the thousands of owners out there who run Sea Frost engine driven refrigeration, as our boat has, who do not have issues with bore glazing.

About three years ago myself and a Beta dealer here in Maine had a long discussion with Stanley of Beta Marine, at the Maine boat builders show, specifically about bore glazing.

Stanley's take was this is a "non-issue" for Beta engines. He insisted they have not seen a single case of bore glazing in a Beta / Kubota block. Not a single one (as of three years ago). This is the US distributor of Beta engines and a guy who has been working with diesel engines his entire life. He is one of the more honest guys in the business and if we had to replace our Westerbeke tomorrow the guy who would get the engine sale....

He also admitted they have lots of customers who idle to charge. I suspect a lot of this is a CYA from the manufacturers point of view and with some engines there is more truth than on others..

The Universal M-25 is the same block Beta uses...... He did say that on some older Volvo's, some Yanmar's and some Vetus/Westerbeke/Mitsubishi blocks that this can be worse. That said we have a Westerbeke/Mitsubishi that has zero bore glazing and more than half its life spent idling. You simply don't get to 3600 hours on a 2002 engine, even when cruising full time as the PO's did, without idling the engine. They had no gen set and only had an 80W panel and a 50A stock alternator. The trick is after idling the PO's, and us always, run it hard.

I think the worry over this is a tad overblown if you otherwise care for and use the engine properly...

So can it happen? Yes, in certain cases I think it can. Does it happen regularly? Not that I have seen or heard of and almost all my customers, being on moorings, idle to charge....

 

[Don S/V ILLusion]

So there we have it.

No consensus. I love the internet.

 

[Calif. Ted]

Someone better tell the guys down at the fire station, they've been leaving their equipment idling for long periods since they switched from gas to diesel about 1970.

 

[jviss]

Thanks, Jesse, for starting this thread, and for the effort you made establishing the context with your excellent post.

I think you set up a straw man argument, presumably unintentionally, with your initial comments about idling. I don't agree with your definition. Idling is not just about engine speed, it's about load. If you look at the performance curves for these engines you will see that they generate half their rated output at 1400 RPM, and the torque peaks at 1900 RPM (example M25XP). Sure, no load with min speed set to 1000RPM and gear in neutral is idling, but loaded at 2, 4, 6 HP to charge batteries at 1,000 to 2,000 RPM is not idling.

Second, your quote from your owners manual is for break-in, not operation after break-in. This is well known, and applies to gasoline engines as well as diesels. Same requirement is presented in Mercury outboard manuals, for example.

Finally, the intended application here is for a variable-speed drive for a boat, where one sets the speed via a lever based on how fast they want the boat to go, and the engine's governor adjusts the fuel flow to maintain that speed. More fuel when more power is required to maintain that speed. There is no consideration or concern given, in this application, to the amount of power produced, as a parameter that is either selected or managed. This, by the way, is nearly identical to the application that these engines were developed for, small tractors, 'though with the tractors the engine is usually either idled or run at full RPM, and a hydrostatic transmission determines drive speed. The governor adds fuel according to keep the speed constant with increased load. So, cutting the grass, or running an auger off the PTO, same system, vastly different loads.

If this was a diesel-electric boat and you could run the engine at constant speed and within a specific power output band, yes, you'd have a very different system.

I guess you might suggest one would be better off having an 18kW head connected and just heat seawater if necessary to keep the load up around 80%, whether motoring or charging, and this would somehow be better than what we're doing? Or carry a gasoline portable generator to avoid "trashing" one's diesel charging batteries? Based on my experience, and that of literally millions of sailors, it's just not necessary. Even if consider it a consumable, that you are simply going to have to de-carbonize the top end every 3,000 or 5,000 hours, and, as Mainsail discovered, find your cylinder walls not glazed, that would be less costly, less cumbersome, more convenient and safer than carrying around a gas portable; but I digress.

Here's a thought: let's commission a long-term, say, multi-decade study, with thousands of boats, and then see whether this use pattern "trashes' diesel engines. Oh, wait - that's been done.

Seriously, I'd like to hear from people who have had engine troubles that are attributable to charging batteries.

My view: is this kind of engine suitable and economical for this application, primary motive power plus battery charging, with good economy, safety, reliability, and longevity? Answer: yes.

 

[All U Get]

Someone better tell the guys down at the fire station, they've been leaving their equipment idling for long periods since they switched from gas to diesel about 1970.

Six years ago I bought this 40 year old backhoe that had been abused by many. The engine is starting and running better now since I changed the oil/gunk and filter. It smokes, groans, and spits soot from the exhaust but sure beats using a shovel. I don't think any service work had been done on it in the last 15 years so I believe they can take some abuse.

All U Get

To add also there aren't glow plugs to start, just a squirt of Snap ether.

 

[JK_Boston_Catalina310]

I think you set up a straw man argument, presumably unintentionally, with your initial comments about idling.

I think you may be right. As you and MaineSail pointed out, there is a load related to charging the batteries that I wasn't considering.

But that's why I started this post, to get this kind of dialog to help me make a better decision about what I need to go cruising.

Thanks for the reply.

 

[thaeni]

I can't Yanmar would design a sailboat engine that had to be run
hard all the time.....

 

[sesmith]

I used to have a pretty large Cat diesel in a GMC Kodiac tool truck I had (I used to own a tool sales franchise). The truck literally idled much more than it ran. This was before NY had a 3 minute idle limit due to emissions. I did oil tests with every service, and that engine never had any issues with many years of use, and never used oil.

On the other hand, the little 1GM10 in my boat sounds kind of ugly at an idle (but you get used to that friendly little sound). The only time I "idle" it is between shifts. I step the speed off idle to warm it up and cool it down. Other than that, I run it. Hope the little bugger lasts forever. FWIW, with solar charging I never have to run it for any other reason than to move the boat.

 

[Rick]

Why is it that the bigger the diesel, the lower the loaded RPM? A locomotive sure as heck doesnt pull all those cars at 3000 RPM like my trusty little 3GM30F does. Why dont they glaze over? I dont like letting my engine "idle" because I feel it shortens the life of my engine mounts with its balance at 800 RPM verses 1000.

For that matter... why do they call it a shipment when its in a truck and cargo when its on a ship?

Hmmmm

Very interesting read this thread is tho

 

[Gunni]

Well, I do know something about diesel locomotives...their traction motors are electric, the diesels simply spin electric generators. This concept was all the rage for sailboats a few years ago, and then not so much.

 

[RichH]

Well, I do know something about diesel locomotives...their traction motors are electric, the diesels simply spin electric generators. This concept was all the rage for sailboats a few years ago, and then not so much.

The diesel engines used as prime movers in Diesel Electric AAR applications are a very far far different animal than highway, off-highway or marine diesels. These are fairly low speed (rpm), looong stroking, diesels.

an example:
EMD V16 EMD GM16V265
Power Output - 6,000 hp or 4,470 kW at 1000 rpm; Idle - 200 rpm; Full speed - 1000 rpm


An other example (from Yanmar) is that in the EU the newer Yanmars come with the option of an integral 'genset' .... an 'alternator package' that is positioned/mounted BETWEEN the engine proper and the transmission - an 'insert'. Its meant to run at quite low speeds for 'charging', etc. when at anchor, etc.

 

[jviss]

An other example (from Yanmar) is that in the EU the newer Yanmars come with the option of an integral 'genset' .... an 'alternator package' that is positioned/mounted BETWEEN the engine proper and the transmission - an 'insert'. Its meant to run at quite low speeds for 'charging', etc. when at anchor, etc.

I'd like to know more about that. Do you have a link?

Thanks,

jv

 

[RichH]

I'd like to know more about that. Do you have a link?

Thanks,

jv

Go here for the Yanmar integral genset 'insert': http://www.powerequipment.com.au/products/marine-generators/flywheel-generator

At this time it 'seems' still only 'dealer talk' in the US and nonEU; and, only applicable to the 3JH5E of 4JH5E diesel engines. All Ive seen is 230v.

 

[jviss]

Thanks Rich!

jv

 

[Steve Dion]

Some clarification!

http://www.yanmarhelp.com/operate.htm

Who should you believe? We charge out batteries & heat water when on the hook, but try to minimize the time.

 

[Nom De Guerre]

Some clarification!

http://www.yanmarhelp.com/operate.htm

Who should you believe? We charge out batteries & heat water when on the hook, but try to minimize the time.

Just to be clear, that is not a website affiliated with Yanmar.

 

[jviss]

Some clarification!

http://www.yanmarhelp.com/operate.htm

Who should you believe? We charge out batteries & heat water when on the hook, but try to minimize the time.

Thanks, Steve, but reading it, it sounds more like folklore than authority; for example, they interchange load and RPM, and declare battery charging "no load," which it isn't.

Answer: don't believe them!

Plus, that source seems specific to powerboats.

Once an engine is broken in properly, i.e., the rings are seated, just don't worry about it.

 

[jviss]

(Im not going to tell you that severely glazed engines can be remedied by dumping or injecting a mixture water and 'cleanser' into the air intake to scuff the cylinder walls, I'm not going to do that).

This is exactly what Westerbeke did with those big, diesel powered, emergency backup generators. I don't know that I'd do it, as I don't have a dynamometer to load the engine down, but I can't imagine how it would hurt the engine (having personally rebuilt several engines); the abrasive would ultimately be harmlessly blown out the exhaust. I know they changed the oil when they were done with this.