Yanmar RPM question

PaulK · Jul 25, 2010

Running diesels

My understanding was that simply running the diesel was not the best thing to do: it is supposed to have a load on it, like pushing the boat forward. Simply charging the batteries is not supposed to be sufficient load to get it really working, so on voyages we shut down after an hour's daily charge; it's not helping the engine to run it unloaded - it's just burning fuel. What guidelines are you using for engine-hours per year that you feel compelled to motorsail?
Though diesels can run continuously for weeks or months on end, I don't see the need to use ours that much.

filthy liberal scum · Jul 25, 2010

running any engine under no load will not harm it!

think about it. truckers will let their rigs run at idle for hours to keep warm in their rigs while sleeping in the winter, like wise to keep the ac going in the summer. if running them with out a load does harm, would they be doing this to their very expensive big rigs? this is a lot of bunk that it will do harm.

Liam · Jul 25, 2010

While it is true that some big rig truckers will let their diesels idle for several hours, they often follow that with running really hard for a tousand miles. Running the diesel hard IS good for it.

That said, I have worked on a number of marine diesels that are 30 year old rust balls that run for 10 minutes at a time 2-3 times a year... Although they are not in the best of shape and I wouldn't trust one to take it cruising, they still manage to start and run for 10 minutes 2-3 times a year.
A well made marine diesel is a really hard thing to kill!

Stu Jackson · Jul 25, 2010

Jack, among other things, running for extended periods at a constant speed should be avoided. What you did was just fine. Open 'er up to WOT every so often, too.

Liam · Jul 25, 2010

PS; My current boat has a 3gm30 yanmar. In the last 6 years I have put 800 hours on it mostly running at 2400-2600 rpm. Oil changed every 50 hours. It is just like new.

CarlN · Jul 25, 2010

The real problem comes from long periods of idle (or close to idle) speeds. This keeps the engine from getting hot enough and carbon builds up. Above 2000 RPM for most engines will be fine and save you substantial fuel.I'm not sure which engine you have but you can probably find a graph from Yanmar that shows fuel/RPM. It's not a linear relationship. I bet that 400 RPM drop reduced your hourly fuel use by something like 50%

To be extra conservative go to your 2800 speed for a few minutes per hour. In the Mack Boring engine class they also recommend that after a long period of slow running (such as a long run into a harbor) before shutdown give the engine three "gooses" in neutral right up to 3000 to blow out any carbon. If you have a turbo model, then let it idle again a couple of minutes before shutdown to let the turbo slow back down.

Motor sailing over just motoring is a great "green" thing to do if there's some wind not on the bow. The motoring increases the apparent wind speed and moves the angle forward. This will help get more energy out of the sails. Do be cautious not to run the engine with a lot of heal. Some engines can have lubrication problems when at too much of an angle. I'm not sure about your engine but I'd guess you should stay at less than 20 degrees.

Carl

Ross · Jul 25, 2010

I posted a link about this a few weeks ago. Yanmar says that if you run at low speed for several hours then about every two hours you should run at full throttle for 15 to 30 minutes to clear the engine. trolling would be a good excuse for running slow for a long period and moving to a different area would be a good reason to run hard.

Paul Cossman · Jul 25, 2010

Running Yanmar with low RPM

I have heard and read about all the recommendations for not running Yanmars (and other marine diesels) without an adequate load. I do know that I am doing the wrong thing, but I thought I'd throw into the mix what has been my experience, not my recommendations.

My 1991 Yanmar 4JH2-TE 62 HP turbo has a little over 5,000 hours on it. During my first two-year cruise I used it to charge the batteries, and often ran it a couple hours a day, w/o a load other than a 130 amp alternator, at about 1500 to 1800 RPM. (Now I have a 5 HP Kubota I use to run the alternator). During that cruise, and my subsequent four-year cruise, I would cruise at 1500 to 1800 RPM when motoring to conserve fuel due to the distances involved. (The fuel savings are substantial). Now, while coastal cruising, I routinely cruise at 1800 to 2000 RPM.

In 2001, before the second cruise, I removed the exhaust manifold to check out the carbon buildup. I replaced the mixing elbow out of nothing more than an abundance of caution (and now wish I had only acid-bathed the bronze unit--but you learn as you go). But the significant thing was the amazing lack of significant carbon buildup; I was surprised. Granted, I didn't remove the head, and right now I can't tell you what my compression is in the cylinders. But I maintain the engine in a manner far beyond the manufacturer's recommendations, and run it in accordance with the manufacturer's specs except for the low RPM running.

The engine still starts and runs flawlessly. I know I'm doing wrong, but I also know that (so far) it hasn't meant any problems. Just thought I'd throw in my experience from one who consistently under-revs and under-loads a Yanmar.

quadrille38 · Jul 25, 2010

I'm a manual reader from the get go. There is a reason manufacturers go to the trouble to write and publish them and I've found that whether it is a lawn mower, car or marine engine reading and following the manufacturers recommendations has served me very well.

On the Yanmar engine, the manual gives instructions on a break in period for new engines, operations and maintenance of the engine, and anything else you need to know.

Yanmar recommends running the engine at load and not letting it loaf along as the cylinders can carbon up and cause excessive wear. They also recommend that if you've had a long period of low speed running that you rev the engine several times at a high rpm before shutting it off.

oceanbird · Jul 25, 2010

My experience is with larger diesel engines running alternators. If the engine was run on no load or light load (less than say 60%) the bores would glaze and that would allow a certain amount of engine lubricant oil to blow past the rings and make its way into the exhaust manifold. The exhaust manifold would allow the oil to drip out and down the side of the engine ( this was called slobering). The idea was to run the engine at 100% load for a period of time to remove the bore glazing. After this the slobering stopped. If run at light load for too long the bore glazing would be irreversable.

I guess the same principal applies to the smaller engines. That is why I think that running a diesel for an extended period on light load is not good for it.

Steve Dion · Jul 25, 2010

Here is an excellent source for your Yanmar Questions.

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

Buck420 · Jul 26, 2010

Ditto Paul

Paul Cossman said:
I have heard and read about all the recommendations for not running Yanmars (and other marine diesels) without an adequate load. I do know that I am doing the wrong thing, but I thought I'd throw into the mix what has been my experience, not my recommendations.

My 1991 Yanmar 4JH2-TE 62 HP turbo has a little over 5,000 hours on it. During my first two-year cruise I used it to charge the batteries, and often ran it a couple hours a day, w/o a load other than a 130 amp alternator, at about 1500 to 1800 RPM. (Now I have a 5 HP Kubota I use to run the alternator). During that cruise, and my subsequent four-year cruise, I would cruise at 1500 to 1800 RPM when motoring to conserve fuel due to the distances involved. (The fuel savings are substantial). Now, while coastal cruising, I routinely cruise at 1800 to 2000 RPM.

In 2001, before the second cruise, I removed the exhaust manifold to check out the carbon buildup. I replaced the mixing elbow out of nothing more than an abundance of caution (and now wish I had only acid-bathed the bronze unit--but you learn as you go). But the significant thing was the amazing lack of significant carbon buildup; I was surprised. Granted, I didn't remove the head, and right now I can't tell you what my compression is in the cylinders. But I maintain the engine in a manner far beyond the manufacturer's recommendations, and run it in accordance with the manufacturer's specs except for the low RPM running.

The engine still starts and runs flawlessly. I know I'm doing wrong, but I also know that (so far) it hasn't meant any problems. Just thought I'd throw in my experience from one who consistently under-revs and under-loads a Yanmar.

Although I only have about 3300 hrs on the (same) 4JH2TE Yanmar in my '01 H420, I have cruised almost identically to the way Paul has for the past 10 years with more or less the same engine experience. Except that, (always having had a gen-set), I have not needed to run the engine at anchorage to charge batteries.

I too, " consistently under-rev and under-load a Yanmar".

druid · Jul 27, 2010

Remember that a lot (Most? All?) recommendations from the mfr are CYA (cover your *ss). It's basically so if something goes wrong, they can point at something and say "did you do that? If not, we're not responsible for any damage...".

Diesels have a reputation for being pretty much bullet-proof, yet we're talking about not running it anything other than 80% load. Rubbish. If you constantly under-load a diesel, there will be more carbon buildup than if you don't. But as long as you run it hard every once in a while, you probably won't notice any difference.

I think the main thing they're trying to put across is that a diesel SHOULD be run hard, and will last longer if you do. As opposed to a gas engine, which will last longer the easier you run it.

druid