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Old 09-09-2012, 09:55   #1
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Diesel Abuse?

I have read on two separate occasions that it is not overall good for diesel engines to simply run a boat out to sail and back again to berth. Why is this not good for diesel engines? What does one do to alleviate any problems this may cause.
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Old 09-09-2012, 10:25   #2
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Re: Deisel abuse?

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I have read on two separate occasions that it is not overall good for diesel engines to simply run a boat out to sail and back again to berth. Why is this not good for diesel engines? What does one do to alleviate any problems this may cause.

Diesel engines aren't like gasoline engines. They are designed to run, and run near full capacity. Ever stop at a truck stop? Ever notice how many of those trucks are left with their engines running? That's because that's what's best for them.

I got a new engine about a year ago. The (certified) mechanic was very clear with me about how to break it in -- not like an outboard, at all ranges, but to run it at near redline for long periods -- go out and motor -- and to run it at red line one hour out of every day. He said that the low - med RPMs most people use taking their boats in and out are the worst thing to do to a diesel. So once you have the boat out, open her up for a while and let her really run.

He said the engine parts, particularly the pistons and valves, "set in" at the speed they're most frequently run at in the beginning.

I can't tell you how many people confidently advised me to run my engine at 2000, or 2400, or 2800 ... but 3200 is the right RPM for my engine most of the time, with red line at 3400.

Each type of engine has different characteristics. Make sure you get your advice about how to use your engine from a certified diesel mechanic and not someone who thinks you need to "gentle" a diesel along. If it's in good shape, it wants to run like a race horse, nearly all out most of the time and flat-out once in a while.
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Old 09-09-2012, 10:25   #3
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Re: Deisel abuse?

In a nutshell, if you don't use 'em you lose 'em. The engines with the least problems are the ones that are run every day, all day, under load.

Fuel needs to course through the filters, pumps and lines, exhaust needs to flow hot and clean, engine needs to run at operating temperature. Cool engines on light load can suffer from varnished valve stems, injectors, injector pumps and coked manifolds and mufflers. Tolerances are tight on diesels, and they rely on the full operating temperature to allow proper performance.

Keep blowing out the cobwebs.
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Old 09-09-2012, 10:25   #4
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Re: Deisel abuse?

It's never good to run an engine diesel or gasoline for short periods without letting it warm up and run under load. Usually not a problem as it's never always windy. The solution is obvious.
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Old 09-09-2012, 10:41   #5
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Re: Deisel abuse?

I would have to say that sailboats that are kept in a marina, and just motored out to daysail, would actually be better served by a gasoline engine. Gasoline engines are much better suited to short duration usage than diesel. Diesel fuel of course is safer to have on board than gasoline, so most boat builders and buyers prefer diesel.
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Old 09-09-2012, 10:45   #6
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Re: Deisel abuse?

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I would have to say that sailboats that are kept in a marina, and just motored out to daysail, would actually be better served by a gasoline engine. Gasoline engines are much better suited to short duration usage than diesel. Diesel fuel of course is safer to have on board than gasoline, so most boat builders and buyers prefer diesel.

Even if I'm only taking my boat out for an afternoon sail, I make sure I run that engine up and let 'er rip for a while. My happiest moment is when I turn the engine off but that doesn't mean I'm going to ignore the engine's needs.
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Old 09-09-2012, 11:31   #7
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Per Nigel Calder's book on diesels, which is very helpful if you wish to do your own maintenance, It's important to minimize running engines without a load like for charging batteries or without warming up because the engines run colder and condensation can create moisture buildup which creates sulfuric acid that can be harmful over time. It also creates more soot which builds up and can be damaging.

This is a matter of opinion, but you won't blow an engine by running in neutral to charge batteries, you will reduce engine life by using a motor like this frequently, but you can still get thousands of hours from an engine and still far more than a gas engine. Commercial engines maintained and run daily can go for 8,000 plus hours.

It also pays to be more paranoid with many commercial engines as they can cost hundreds of thousands.
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Old 09-09-2012, 11:38   #8
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Re: Diesel Abuse?

I've heard these arguments for running the diesels like this for years. But I've yet to have it explained to me in a way that I understand just what it is about diesel engines that makes it better to run them. They don't get hot enough for temp to really be that much of a factor. As far as varnish, does diesel evaporate and varnish up like gasoline does? it's not that volitile, is it? Diesel fuel has a long shelf life. It's also a preservative and lubricant.

If the engine is running, aren't the parts subject to wear and friction that doesn't happen when it isn't running?

The engine life and time between overhauls is expressed as hours since last overhaul.

If that number is, for example, 10,000 hours, I never see someone spec it as "10,000 hours IF you run it all the time and only 5,000 hours if you don't run it".

When I google up "why do truckers leave their trucks idling" I get opinions but no hard facts other than that they like to leave all their systems running while they are sleeping, or they are only stopped for a short time and it's bad to let them cool off and then re-start them an hour later and let them have to warm up again. That isn't valid for boats. Sounds like their issue is restarting them too soon after lunch. Not days later when returning to port.

I'd like to understand it, as we just bought our first boat with twin diesels in it. They have about 3,000 hours on them, and are 26 years old.
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Old 09-09-2012, 11:51   #9
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One reasone that an engine that get's a lot of use will last longer is that the constant change of te,perature creates engine wear. Stopping and staring allows the engiine to cool off, then heat up again. This expands and contracts the cylinders, block, piston and creates more friction and wear. This is why truckers idle insteal of shutting down and restarting. It's also why a diesel that is run all day non stop will run be able to run up so many more hours than any diesel in a sailboat.

Commercial boats install block heaters to always keep the block heated to the exact running temp to eliminate any change of temperature ever, which will extend engine life.
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Old 09-09-2012, 12:05   #10
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Also, As an engine is run the oil becomes acidic and corodes the engine, so a motor with less frequent use will be exposed to internal corrosion over time while it sits. This is why you should change oil immediately before layup and turn over the motor a few times with new oil to coat the engine.
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Old 09-09-2012, 12:12   #11
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Re: Diesel Abuse?

I have no problem running my diesel under low load; to charge the batteries or motor along at 4-5 knots. I've read these threads for years, but you never are going to convince me that it is better for any peice of mechanical equipment to be run hard all the time compared to be run at a lighter load.

I do run it up to high rpm once in a while to clear out the cylinders, and I always run it up to temperature when I do run the engine (and I cool it down afterwards).

In other words, I run my engine just like what it says in my Yanmar manual!
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Old 09-09-2012, 12:21   #12
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Don, How do you cool it down, and why? I just shut mine off and never thought of doing it otherwise. I have heard that engines get hotter when you stop them, but how do you avoid that?
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Old 09-09-2012, 12:23   #13
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Re: Diesel Abuse?

There are more myths concerning diesels than there are Grimms fairy tales. Once you have reached operating temp, do what you need to do and then shut it down. It does not matter if it is running at high rpm or a low one. Lugging the engine is hard to do on a boat.

Diesels run in truck stops because the drivers are running their ac or heaters. Most big truck stops have gone to "Idle air systems" so that trucking companies can save diesel fuel.

Most trucking companies with aggressive oil sampling programs are running oil so long it would blow your mind. It was not unusual to retire trucks after 400k miles without ever changing the oil.
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Old 09-09-2012, 12:31   #14
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I'm professional truck driver. If it is 5 min or more then it is cheaper to shut down the engine instead of keeping it idling. Most truck drivers run their engines because they want to be comfortable inside and because fuel is cheap here in US. Yes it is still cheap. There are no idling trucks in Europe. Most of them have separate small generators/climate control units. Even in Canada separate climate control units become a norm nowadays.
All the talk about how harmful sailboat engine operation is what it is - a talk.
Sure, the engine with 1000 hours of constant work at maximum performance will have less wear and tear than the engine with 1000 hours of stop and go operation, very much like a car with highway only miles.
Yes, it is good practice to run an engine at it's designed performance RPM. Yes, it is important to watch the temperature while idling the engine and bump the RPMs up when it is running cold. Other that that there is not much one can do to improve engine's life.
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Old 09-09-2012, 12:35   #15
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Re: Diesel Abuse?

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Don, How do you cool it down, and why? I just shut mine off and never thought of doing it otherwise. I have heard that engines get hotter when you stop them, but how do you avoid that?
I just let it run at idle for a few minutes to allow the various engine parts to equalize. The amount of time varies depending on how I was running the engine. If I had been running hard I will idle it for around 5 minutes (like the manual says), if I was just lightly running along I will pretty much just turn it off after 1-2 minutes.

If I was running in neutral to charge batteries, or if I had been running lightly for a while, I run the engine up to high rpms for 10-15 seconds and run it back down and repeat this a couple of times evry couple of hours. Then run a minute and turn it off.
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