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Old 01-24-2013, 01:50 PM   #1
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Default Diesel engines.

Most cruising boats these days have diesel engines. I am not a mechanic and have no specific knowledge about the care and maintenance of these beasts, other than that which involves the routine.

Over the years, I have heard people voice their concerns about idling diesel engines without load. I have not always been dilligent about loading my engine when running it; mainly because I think people who do just that, at the dockside, are behaving in a foolish and potentially perilous pursuit.

My deezul engines over several decades have always performed well, and that goes for the ones in my boats and in my vehicles. I have always been a bit sceptical about those who become just a little bit anal over the whole idling the engine thing.

So am I being the foolish one? Those who claim to know about these things go on about glazing the bore and running the engine too cool. Yet my experience is that idling the engine does little other than make a bloody racket.

Is it a myth perpetuated by diesel mechanics? Does it genuinely cause problems which I have avoided by pure dumb luck? Can I safely continue to run my diesel without putting the boat in gear and trying to tow the dock around the bay? Was it once a problem which advanced metal and fuel technology have now overcome?

Is it a bit like the myth that eating chocolate gives you zits...? (ie good faith, poor science)

The thing is I confess to being a hypocrite here. When people have asked me about idling diesels, I have always told them it is bad practice because of the glazing/cooling stuff; yet I have merely been rabbiting that which others have told me, without me being in possession of even the tiniest skerrick of evidence.

So....what's the poop?
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Old 01-24-2013, 02:41 PM   #2
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Don't know much about the science but when on my mooring I run the diesel for about 30 minutes at least once a week to get it up to temperature and to make sure everything is as its supposed to be. can't see me loading it up by whacking it in gear and going round and round the mooring. I have had diesel engines in boats for many years and have followed the same general routine and haven't ever had a problem, dumb luck or not it seems to work for me. I have a Perkins 4 236 in this boat and it was reconditioned about 150 hours ago and honestly only the head needed a bit of a clean up and it had a few thousand hours on it. Guess we best keep doing whatever it is we are doing ... I know freak all about diesels either.

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Old 01-24-2013, 03:28 PM   #3
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Diesels really don't warm up well unless under load. Idleling at normal idle speed, 750 rpms, for long periods is not considered a good idea because the cylinders don't get really hot and the fuel can coat the cylinders and slip past the rings into oil, otherwise called cylinder washdown.

Once they're warm there's no issue, and in fact it's better to let them idle than switch off if you're planning to run again anytime soon. Check out any truck stop parking area to verify that.

The idling thing applies especially to very worn engines. Considering the relatively light duty most marine engines in yachts get I wouldn't worry about it too much. BTW I have an HC licence.
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Old 01-24-2013, 09:40 PM   #4
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It is difficult to get the diesel engine hot enough unless you put on a load. We spent a good deal of time in the last year at a dock--we're back to living on the hook now (yippie!)...and while at the dock, 1x/month we'd run up the engine to about 1100 rpm to get the exhaust gas readings hot enough to indicate we were really warm. Our manifold is water jacketed so the first point of entry fro the pyrometer is after the mainfold. The gasses are already cooling at that point so we have an "experience" scale of temperatures that indicate good heat in the engine. So, even though the cooling water temps remain a rock steady 185-190, the following exhaust temps we have:

350F when at 900 rmp smooth water (just above idle)
400F when at 1100-1400 rpm on smooth water
450F when 1350-1500 rpm on the ocean
530F when between 1400-1700 rpm on a rough ocean
560F *ideal highest temperature usually when about 1700 rpm on the ocean
600F when pushing hard --perhaps motorsailing through a gale and rough seas
630F as high as we'd want to see at the pyro

We note that the engine exhaust temp is a smooth curve increasing, but when it gets above 580F, very little change in the throttle will increase the pyro temperature a huge amount. So we really try to keep below 560F at the location of our pyro. We like to, at a minimum, "bake pizza" which is 450F when underway.

Again, the cooling water temperature doesn't give you any indication of how much the engine is getting worked out--its the exhaust gas temperature that tells the tale.
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Old 01-25-2013, 02:41 AM   #5
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Interested I just googled diesel engine idling myths: From Cummins on down seemingly all sources and research discourages idling for more than a few minutes.

Reasons range from the oil dilution already mentioned above to extra and heavier wear, perhaps due to this effect. Carbon buildup due to very much lower cylinder temperatures and wasted fuel costs. Extra emissions, noise etc. etc. Unless for a very valid reason, there seems to be no tangible benefit from it. Engine life reductions of 20% or more can be expected as well. Plug in the global warming component as well if you like.

All good and healthy food for thought.

Ivo
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Old 01-26-2013, 01:54 AM
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Old 05-05-2013, 05:43 PM   #6
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A little late to the party, but my 2 cents worth;
I only idle a diesel until the oil pressure comes up into the operating range. After that I will run it at about 1000 RPM's or wherever it smooths out. This keeps the oil pressure in the proper operational range and plenty of water flowing through the cooling system. Putting it under load is of no added value once you have proper oil pressure and water flow.
Over the road diesels are set up completely differently from marine diesels, with different oil pumps, injectors and pistons, etc. as they operate at varying speeds for varying periods, whereas marine diesels run, for the most part, at a constant speed for an extended period. This is the main reason buying a cheaper, over the road diesel for a boat, may not be the best move.
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Old 07-25-2013, 10:18 PM   #7
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Default Auzee

You are on borrowed time. You are on thin ice, Auzee. Doubting the sailing Diesel Gods and scoffing at them.

On the other hand if you have been running diesels for 20 years and no adverse effects. Then why rock the boat Auzee. For surely now, that you have opened your mouth and thoughts to everyone, you will be cursed for 20 years with foul tempered diesels.

Please tell me where you have the anchor down, it would be bad luck to be anywhere near you.

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Old 07-26-2013, 08:25 AM   #8
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What an odd response to a question seriously posed.
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Old 07-26-2013, 11:04 AM   #9
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Actually Auzzee I thought that duckwheat's response was pretty funny. Doesn't hurt to have a laugh once in a while even at a serious issue.
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Old 07-26-2013, 12:44 PM   #10
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Thanks Del. I guess you are right. I read and responded after a long day in the saddle and had left my sense of humour in the panniers. Now unpacked and reinstalled, I see the funny side.
Cheers.
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Old 07-26-2013, 01:23 PM   #11
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Now I'll give you the best answer I have.

After I got my most recent boat I was put in touch with a guy in Sydney who Vetus (engine makers) claimed was the best European engine specialist in Australia. He assures me that extensive running on idle will, in the long term, harm a diesel engine and one should not do it for long periods of time without also putting load on an engine. He assures me (without showing me direct evidence) that he's seen engines damaged by lots of idling to the point where they needed rebores and/or significant repairs. On the other hand he says that doing it occasionally interspersed with periods of running under load won't actually do the engine any harm, and in particular running the engine at idle for a few hours every couple of weeks is much better than not running it at all.

I have no reason to doubt him really, he's been messing with diesel engines for around 40 years and seems to know his stuff.

Sorry, that's all I have and it's second hand info.
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Old 09-02-2013, 04:39 AM   #12
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Addressing the original post:


This is why I deal in truth. What some mechanic tells me about my diesel engine is strictly what some mechanic tells me about my diesel engine. It is nothing more until I verify it as fact or fiction. I will find facts myself, thank you.

Science - physics - suggests that this is nonsense. Load means more energy must be used. Sure, an engine can "run away" if it is unloaded; but that would only apply to certain designs; specifically engines designed to be run under load only because they would otherwise "runaway" and have pistons slapping, incorrect fuel-air mixtures, insufficient exhaust back pressure, etc.

If you can, consult the manufacturer of the engine, rather than relying on one or two mechanics. As I do not know the answer, especially not knowing what engine you have, this is all I can offer.
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Old 09-05-2013, 09:34 AM   #13
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Auzzee, glad re yr reply to Del. Re Duckwheat I not only *at first* thought it odd even downright weird eg "you will be cursed for 20 years" etc then when I read "DW Motivational Group Leader and Life Coach" and saw his pic again I just burst out LOL )) its like the over-the-top coach character played by Jack Nicholson in the b film "Anger Management". DW's reply lacked technical advise yet, no bizzel idler he coached in and "motor-vated" a good healthy laugh
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