ENGINE CRUISING SPEED 3QM YANMAR

[RJMRJM]

When motoring or motor sailing my 34ft. older long keel sailboat every weekend I run my 3QM Yanmar 4500 hours engine at around 1600 RPM for 2 or 4 hours dock to anchor each way .My speed is usually around 5 knots or if the sea is up or I am in a hurry (not very often) I might run at 1800.On the occasional at sea passage if the headsea is up I might be running the engine near 2000 revs for a couple of hours.
There seems to be different opinions about this 1600 rpm general speed, What does the Forum think.
Thanks RJMRJM

[a64pilot]

Others will tell you your going to kill it, that you have to pull it guts out for a long life.
I disagree and will tell you to continue as you are and you will be rewarded with a long engine life.
However my belief is not mainstream.
I hold out to those that say you have to run an engine at 2500 or higher for it to last by bringing up that the most longest lived engines are generators, that run a steady state speed of either 1500 or 1800 RPM depending on Hz rate and are identical engines to our boat motors.
I usually don’t get a response, occasionally it’s some I own a tractor or something and have always run it at high RPM and have gotten good service, so that must be the right way to do it.
But most try not explain how it is that a motor that is only run at 1500 RPM can last so many hours, without being raced up every two hours etc.

[Wotname]

There is a something to be said about running your engine below max RPM providing it is loaded at those revs i.e. IMO, running virally unloaded (in neutral) at 1800 is way worse than running it underway at 1800. In general I concur with a64 and I accept he knows way more than I about engines!

The 3QM30 has a max continuous RPM of 2600 and a 1 hour max RPM of 2800. I do believe you should run the engine at max RPM occasionally (and at WOT) just to be sure everything is working properly e.g. temps and pressures remain normal.

Noting trends and abnormalities at WOT will tell you information about your bottom, your prop, your cooling system and your lubrication. Take this time to check blow-by and exhaust colour. Keep a track of oil usage and ease of cold starting. All these will help you determine potential life remaining in the engine.

Others advise getting an oil analysis but I am not sure how cost effective this is for a small engines of this vintage.

FWIW, I use to run my 2GM20 between 1800 and 2200 when wanting a easy motor and between 2800 and 3200 when in a hurry. WOT was 3600 and the max continuous was 3400. I mostly ran it at WOT for about 5 or 10 mins every couple of hours to be sure nothing was going south.

[Compass790]

Originally Posted by a64pilot

Others will tell you your going to kill it, that you have to pull it guts out for a long life.
I disagree and will tell you to continue as you are and you will be rewarded with a long engine life.
However my belief is not mainstream.
I hold out to those that say you have to run an engine at 2500 or higher for it to last by bringing up that the most longest lived engines are generators, that run a steady state speed of either 1500 or 1800 RPM depending on Hz rate and are identical engines to our boat motors.
I usually don’t get a response, occasionally it’s some I own a tractor or something and have always run it at high RPM and have gotten good service, so that must be the right way to do it.
But most try not explain how it is that a motor that is only run at 1500 RPM can last so many hours, without being raced up every two hours etc.

But are any of those generators raw-water cooled? I can't see the reason for running hard out myself except that maybe it slows the Yanmar elbow clogging on a cooler running engine. Just speculation though. Maybe it's better just to clean the elbow more frequently. Definitely more power/rpm in general means more wear so i guess I'd lean on the side of doing what the O.P. has been doing if he's after longer life.
long winded way of saying I agree

[coopec43]

YANMAR 3YM30 MARINE ENGINE

Now for the boring bit. The Yanmar 3YM30 develops 28.6hp at 3600rpm or 26.9hp continuous at 3490rpm from its 1115cc OHV engine with gear-driven pushrods and two valves per cylinder. The cylinder bore is 76mm and stroke 82mm, which helps the engine achieve good combustion chamber efficiency. The maximum torque output is 69.5Nm at 2000 to 2500rpm. The engine has an A rating, or up to 500 hours of running per year with a maximum of five per cent Wide Open Throttle operation.

AND

Once the technique for engaging overdrive had been mastered, we were able to maintain engine load at all rpm, so important for the 3YM30 which should be run continuously at or greater than 2500rpm to prevent cylinder bore glazing from insufficient load

https://www.tradeboats.com.au/tradea...-engine-review


Clive

[Wotname]

Clive, just how is this relevant to the OPs 3QM engine?

[coopec43]

Originally Posted by Wotname

Clive, just how is this relevant to the OPs 3QM engine?

OMG! Sorry, I've got my wires crossed somewhere.

But as a rule of thumb diesels should be run at around 70% of maximum rated output RPM. If they are run without a proper load problems will occur - cylinder glazing etc.

I hope that's relevant.

It's late so I think I better go to bed.

Clive

[Bruce Beard]

This is an interesting question that seems to come up over and over.
Like most simple questions I believe that the answer is... “it depends”.
So many small diesels die well before their time.
I do believe that a certain amount of load is necessary for long life but how much? I do not think there is much harm in working a small diesel hard once in a while and in fact the owners manuals that came with the two Yanmar sailboat engines we owned suggested that the engine be used to push the vessel to hull speed for an hour once a month or something along those lines.
As we have now gone to the dark side and engines are both obscenely expensive and well, necessary, I have been reading a lot on the subject.
All of the best descriptions of diesel engine lifespan talk about the importance of propeller pitch. Running any diesel in an overpitched state is detrimental to its ultimate lifespan. This is something that is pretty much ignored by the sailing community. Apparently, it is a bigger deal than is commonly understood.
Another little helpful model about engine life or how many hours an engine can last uses gallons of fuel consumed to determine lifespan.
In other words, running an engine fast all the time will wear it out faster than running at lower speeds or at lower output. It just makes sense!
All of this assumes proper maintenance of course.
None of this addresses the issue of loading the engine occasionally.
I do know that in the world of common rail fuel systems, engines run fewer slobbering issues so apparently the need to run it up is diminished.
In that, QM series Yanmar engines have a reputation of lasting forever and most well cared for sailboat engines die of old age rather than terminal wear, I don’t see the harm in running it up for an hour a month or so.
Kind of like having your cake and eating it too...

[01kiwijohn]

You also have to consider how the prop is pitched. Yanmar gives figures for each engine installation, on how much reduction in rpm there should be when running the boat at wot, compared with its high idle rpm. Many boats are incorrectly pitched, giving good speed, at low rpm, but the engine overloaded.

[Rough Magic]

Every engine/configuration has a 'sweet spot' where the fuel burn is most efficient. On my Cummins, that was 2000-2100 of a top of 2600. Or about 75-80% of max. These were set by builder to manufacturer's spec. I was told to expect 8 to 10K hours if run this way. Sold the boat way before, the new owner is still running fine.

[Cadence]

Originally Posted by a64pilot

Others will tell you your going to kill it, that you have to pull it guts out for a long life.
I disagree and will tell you to continue as you are and you will be rewarded with a long engine life.
However my belief is not mainstream.
I hold out to those that say you have to run an engine at 2500 or higher for it to last by bringing up that the most longest lived engines are generators, that run a steady state speed of either 1500 or 1800 RPM depending on Hz rate and are identical engines to our boat motors.
I usually don’t get a response, occasionally it’s some I own a tractor or something and have always run it at high RPM and have gotten good service, so that must be the right way to do it.
But most try not explain how it is that a motor that is only run at 1500 RPM can last so many hours, without being raced up every two hours etc.

I would have to agree. I like running no place near rated HP RPM. But an engine occasionally needs the eliminate cylinder ridges. If not as an occasional practice then done, good by rings.

[Mike Banks]

If you set up your propeller and engine and gearbox ratio, so that the maximum torque revs of the engine (they supply this data from their test) is achieved under your maximum loading, you are pretty much on the money as far as correct propeller selection.

Most diesel engines are happy running at their maximum torque revolutions at full load. Whatever they are--it is usually their design operating RPM.
That may sound extreme--but it isn't. They LOVE to wok hard.

[coopec43]

Originally Posted by Mike Banks

If you set up your propeller and engine and gearbox ratio, so that the maximum torque revs of the engine (they supply this data from their test) is achieved under your maximum loading, you are pretty much on the money as far as correct propeller selection.

Most diesel engines are happy running at their maximum torque revolutions at full load. Whatever they are--it is usually their design operating RPM.
That may sound extreme--but it isn't. They LOVE to wok hard.

Mike I couldn't agree more.

When I ordered my prop the specialist asked.
1. The RPM for the diesel at the "continuous"
2. The HP at the continuous revs.
3. The gearbox ratio.
4. Maximum diameter prop I could "swing".

The diesel is a Perkins 4-108 producing 51 hp at 4000 rpm (intermittent rating) and 39 hp at 3000 rpm (continuous rating)