# Max Cruising RPMs for Yanmar



## shopkins (Jun 4, 2001)

I have a 1988 Morgan Classic 41 with an original Yanmar 4JHBE with 2,440 hours. It is in excellent condition, rigorously maintained and with no problems whatsoever. The rated horsepower is 44 @ 3600 rpm. Are there any opinions on a safe, long-range maximum cruising rpm for this engine? My S.O. insists I not exceed 2700 rpm and I can't see crossing the Gulf Stream from Miami to Cat Cay at a VMG of 2 knots if we have to motor. Thoughts appreciated.


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## NOLAsailing (Sep 10, 2006)

You should be at about 80% of max RPM. If max is 3600, then you need to be about 2880. That should be more than enough to push you at hull speed.


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## indyshope (Oct 19, 2005)

be certain that the RPM / tach guage is reading accurately. most guages need to be adjusted while using a timing device.


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## DrB (Mar 29, 2007)

*Forever Cruising.....*

NOLAsailing gave you excellent advice. Provided the engine is operating well and taken care of, 80 to 85% of max RPM is often recommend for a Yanmar diesel (at least mine).

If you have any concerns, give Yanmar a call and they'll advise you in what's best for your motor.

DrB


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## artbyjody (Jan 4, 2008)

In general most Yanmars operate at cruising at 2300-2500 RPM - anything above and beyond will just burn more fuel without any truly appreciated returns in speed.


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## TSOJOURNER (Dec 16, 1999)

I have a Yanmar 4JHE and regularly motor at 2700 to 2800 RPM.


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## camaraderie (May 22, 2002)

I had one and cruised at 3000 all the time with no ill effects and this was the RPM recommended to me by maxboring (the Yanmar distributor) in a seminar.


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## NOLAsailing (Sep 10, 2006)

artbyjody said:


> In general most Yanmars operate at cruising at 2300-2500 RPM - anything above and beyond will just burn more fuel without any truly appreciated returns in speed.


It's not just about speed. It's about doing what's mechanically best for the motor. Under-revving a small diesel has a number of ill effects.


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## camaraderie (May 22, 2002)

artbyjody said:


> In general most Yanmars operate at cruising at 2300-2500 RPM - anything above and beyond will just burn more fuel without any truly appreciated returns in speed.


Jody...I can assure you that I motored appreciably aster at 3000 RPM's than at 2500...and at considerably higher cost in fuel. The tradeoff is an individual choice...and motoring on the ICW for 8 hours rather than 10 hours was often a good trade off for me. Doesn't matter much in and out of harbors buton long motoring days...that extra 1/2-1 knot can be quite important.


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## artbyjody (Jan 4, 2008)

camaraderie said:


> Jody...I can assure you that I motored appreciably aster at 3000 RPM's than at 2500...and at considerably higher cost in fuel. The tradeoff is an individual choice...and motoring on the ICW for 8 hours rather than 10 hours was often a good trade off for me. Doesn't matter much in and out of harbors buton long motoring days...that extra 1/2-1 knot can be quite important.


Hence why I stated the rpm value as generally speaking  But good to know...and yes always a trade-off... I probably am more like you as time motoring is of the essence - when sailing - don't care


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## Rockter (Sep 11, 2006)

Keep the revs up, but don't thrash an older motor. You can usually tell if the motor is content. Watch for black smoke, excessive oil consumption, overheating and final drive vibrations.

My olde Volvo MD17C seems content at 1800 rpm. Max power is 2500 rpm, but it does not rev to more than 2250.

In to a stiff headwind we'll sit at 2000 rpm for long periods, but rarely more than that.

I have left the engine compartment side panels permanently open so I can check the old motor's vitals.

They need TLC as they get older.

They do not need thrashing.


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## Ilenart (Jul 23, 2007)

*Similar problem / issue*

as my engine will not rev above 2,100rpm when the maximum RPM is 4,000 and continuous rating is 3,200 (or 80% which seems to be a common continuous max RPM rating). My engine is about the same engine hours as yours but different make (Nissan SD33 98HP).

I think my problem is the device that sets the maximum RPM needs adjusting. Letting my mechanic deal with it as the manual quotes four different ways of adjusting it depending on whats fitted to my particular engine (probably be a fifth  )


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## beej67 (Apr 2, 2008)

I don't think the tach on my Yanmar 3gm30f was ever calibrated properly, because it gives values far too low than I would expect based on listening to the engine. (my dad installed the engine, and he's pretty notorious for overlooking "details" like that, heh) I do it all by ear now.

I say, push it near to the top, get near hull speed, watch your exhaust to make sure you're not burning oil. Diesels love to be worked. I motored from Apalachicola to Destin and back, strait across the Florida Middle Grounds during a week of dead calm, at about 18 hrs / day with occasional 'rests' of the engine, about 3 years ago. My engine loved me for it.


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## Cruisingdad (Jul 21, 2006)

I was told by Yanmar to run their engines hot and heavy. I was told (and can probably attest) that the problem with most sailboaters is they run their engines at low rpms because they think it is good for it, they want to conserve fuel, or want to reduce noise. However, on Yanmars, I am not sure that is very good for the engine due to carbon buildup. 

I cannot attest for the exact RPM on your engine, but seems like 2800. Call Yanmar distributor and they will help. Also, don't rely too heavily on your tach gauge. They are renound for being off.

I worked with Eddie at Boatswain - 866-353-bosn, or DOug Dykens at Mastrey Engine, 800-545-4574. 

They should be the final answer.

- CD


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## petegingras (Mar 29, 2007)

Jason,



> Under-revving a small diesel has a number of ill effects.


The only effect of low RPM, that i'm aware of, is carbon build up in on the piston and an walls of the cylinder. Now that has a simple fix of revving the engine or running it at a higher RMP for a period of time. You'll see white smoke emitted from the exhaust, and that's the aforementioned carbon. What else are you referring too?

As for the comment burning oil, NEWSFLASH: all diesels are burning oil! So have extra aboard and check the levels frequently.

I concur with the Yanmar's advice, or have been advised by their techs, they love to run under a good quality load.


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## TSOJOURNER (Dec 16, 1999)

Don't baby the newer high speed diesels! 3000 is a good number. Keeping the oil hot, the fuel flowing, and letting the tranny oil heat up to operating temperature is a good thing and will extend engine life. If you are reaching hull speed at 2500 with the newer engines chances are you are over propped and can expect a significantly shorter engine life. I put 400 hours running at 3000 sometimes for 3 days straight with no ill effects, black smoke or otherwise. Just make sure everything is chafe protected!!


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## TSOJOURNER (Dec 16, 1999)

I run the little 1GM in Lola about 3000-3100 most of the time. It doesnt use much fuel and seems to be nice and happy with that.


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## hphoen (Apr 3, 2003)

With a clean hull and prop, I can motor at 6.5 kts at 2700 rpm on my 4JH3BE. I don't like to burn the fuel to run it at 3000 for an additional half knot or so. That being said, every hour or two, I rev it up to 3000 for 5-10 minutes to "blow out the carbon".


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## artbyjody (Jan 4, 2008)

So in researching I found this handy little table for max rps at 85%


GM - 4JH - 3/4JH2 series​2900rpm​YM series Depending on WOT rpm​2600-2900rpm​4LH and 6LY series​ 2650rpm​ 6LP and 3/4JH3 series​3000rpm​3/4JH4 series​2400rpm​ 6CX series​2200rpm​
source: Yanmar Marine Engine Help


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## hphoen (Apr 3, 2003)

petegingras said:


> The only effect of low RPM, that i'm aware of, is carbon build up in on the piston and an walls of the cylinder..


Ditto, but I'd add another--soot buildup in the mixing elbow (where the exhaust gases cool down). Get enough in there and the engine falters.


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## beej67 (Apr 2, 2008)

hphoen said:


> Ditto, but I'd add another--soot buildup in the mixing elbow (where the exhaust gases cool down). Get enough in there and the engine falters.


That is the #1 first thing I look at when I don't have good flow out my tailpipe.

(#2 is the impeller)


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## theartfuldodger (Sep 4, 2006)

My manual for the 3ym30 I installed recommends cruising rpm of 3200rpm, and have done this for the last 750 hours, with ill effects, as well have fined tuned the valve adjustments as well the injection timing and have even a more cleaner burn engine. All oil samples thus far have shown nil engine wear.


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## Cruisingdad (Jul 21, 2006)

*Carbon Buildup*



hphoen said:


> Ditto, but I'd add another--soot buildup in the mixing elbow (where the exhaust gases cool down). Get enough in there and the engine falters.


Please correct me if I am wrong.

Carbon buildup is BAD. I noted earlier that it was said that you just punch it every once in a while and clean it out. My undersatnding, although there is some fact to that, is not entirely the same.

The mixing elbow was mentioned so I will start there as I have had to deal with high backpressure issues (not on my boat) - but seemed to have gotten quite an education.

If you are getting high back pressure, the rear cylinders will get hot. You will also get a carbon buildup in those cylinders. That carbon then slowly scores the cylinder walls. That in turn causes a compression loss. Compression loss then causes engine performance loss and finally total failure.

That is why you do not run your engine for long periods of time at low RPM's. Please explain where I am wrong. THis is what has been explained to me by Mastery, Boatswain, Yanmar, Valiant, and many other marine engine specialists that had to get involved. In essence, it is the reason that running your engine without a load is a bad idea - carbon buildup.

One of the key tests for a diesel's health is a compression test. Each of the cylinders should be within 10% (depending upon the engine) of each other. If they are not, there is an issue somewhere. I know that we found many rear cylinder failures due to carbon buildup due to a mixing elbox without the proper sized exaust tubing.

Again, I do not pretend to be a diesel mechanic, just repeating what I have learned and been told over the years. Carbon buildup and cylinder scoring is like diesel cancer, a slow, quiet killer.

Thoughts?

- CD

Just an edit and feel fre to jump in: Not running at a load causes the cylinders to not have the proper backpressure and will cause scoring.


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## theartfuldodger (Sep 4, 2006)

rear cylinder carbon would be an issue if the fuel system was fed from a central system like in a carburated engine, but being a diesel engine has individual injectors, there should be a constant fuel and air supply to each cylinder. The main issue is constant maintenance. Your doctor does blood testing to know your body and its internal issues. Oil testing does the same and warms of pending issues. This is not expensive at all.


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## jimmalkin (Jun 1, 2004)

Taronga - 4JHDTE (1991) - runs at 2,800. This older version smokes more than the newer ones (according to mechanic and Yanmar) but with the right compression we still are running clean, the elbow is clear and not using much oil. Injectors are worth checking every several years. Biggest issue we have is not running the engine under load for long enough periods of time.


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## Bermudahigh (Nov 17, 2007)

on my 18 hp yanmar's i was told by yanmar to run at 90% power....3000-3100 rpms. no problems, no issues.


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## trantor12020 (Mar 11, 2006)

SVDistantStar said:


> I run the little 1GM in Lola about 3000-3100 most of the time. It doesnt use much fuel and seems to be nice and happy with that.


I'm curious to know your prop pitch, 2 or 3 blades and approx speed you're doing at 3100rpm on Lola. Thanks.


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## eryka (Mar 16, 2006)

Just to echo previous advice ...

I spent all day Monday in a Yanmar seminar (Mack Boring); their guidance was to punch it for about 30 min every 10 hrs or so to blow the carbon out. "Punching it" under load meant, on the brand new 4JH's they had just delivered, the governor is set at 3300 rpm, the engine can go 3600. That's 5% of the total running time.

The other 90% of the time, 2800 rpm would get the boat to hull speed. The fuel consumption curves for this one were 1.3 gph @ 2800; and 2 gph @ 3300.

The last 5% - don't shut the engine down hot. Let it idle for 5 min or so to cool off first.


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## petegingras (Mar 29, 2007)

> This older version smokes more than the newer ones


jimmalkin,

i believe they told you this, but i think that smoke is factor of many things, and if the mechanic said it, that's one thing, Yanmar, they're smarter than that. Black smoke i think good...engine running under load, smoke is oil. White smoke i think fuel contaminant, i.e. water, tank growth.

And Ken you're right


> I'm curious to know your prop pitch


pitch is a factor to consider correct load at different RPM.


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## theartfuldodger (Sep 4, 2006)

If an engine is not a smoker all the time the smoke under load will be unburt fuel, as is the same in the Auto industry


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## ebs001 (May 8, 2006)

One of the important factors which nobody has so far mentioned is whether the max rpms are no-load or loaded. The max rpms that you get from the engine spec are no-load. Loaded you can reduce that number by around 300 rpms, then take 80-85% of that as your cruising speed. It is a good idea to know that your tach is accurately reflecting the rpms of your engine. Be aware that changing your alternator can change the tach reading as well.


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## TSOJOURNER (Dec 16, 1999)

petegingras said:


> jimmalkin,
> White smoke i think fuel contaminant, i.e. water, tank growth.


more likely blown head gasket. enough water in the fuel to cause white smoke means your racor is full and it won't be blowing white smoke for long! If you see black smoke you need to throttle down, and if it doesn't go away something is askew (wrong prop, back pressure being most likely). The "older diesels smoke more" theory doesn't hold up. Ideally, the exhaust of a 1 cyl 8hp all the way up to a supertanker should be clear under normal operating conditions.


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## Ilenart (Jul 23, 2007)

ebs001 said:


> One of the important factors which nobody has so far mentioned is whether the max rpms are no-load or loaded. The max rpms that you get from the engine spec are no-load. Loaded you can reduce that number by around 300 rpms, then take 80-85% of that as your cruising speed.


Not sure if this is correct. My engine handbook states maximum output of 4,000 RPM and does'nt specify whether it is load or unload. However in the detailed engine manual it states maximum no-load at between 4,500-4,600.

I think you have research your particular engine to work out what your engine specs are assumming


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## ebs001 (May 8, 2006)

This was advice I got from a mechanic and we looked at the specs on a number of engines. You can test it out yourself. Put the engine in neutral and take it to max. Then do it under load. If you are loosing much more than 300 RPMs then you are over propped and loosing less under propped ie too much or too little pitch.


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## TSOJOURNER (Dec 16, 1999)

ebs001 said:


> This was advice I got from a mechanic and we looked at the specs on a number of engines. You can test it out yourself. Put the engine in neutral and take it to max. Then do it under load. If you are loosing much more than 300 RPMs then you are over propped and loosing less under propped ie too much or too little pitch.


For some reason I feel the strong urge not to find the max RPM. Never done it on my boat and don't want to. Reminds me of working on a car when I was in HS. I reved up the engine from the throttle body, and the gas pedal stuck! Tach was pegged at 8K by the time I got her shut down. It lived, but that was the last time I will ever redline an engine, unless of course I'm trying to destroy the thing 

Now here is a question: If I throttle up, say to 2800 RPM, with no way on the boat, a dead stop the engine quickly reaches a specific RPM. As the speed of the boat sloooowly increases and reaches its equilibrium (about 5 knots at 2800) the RPM has not changed. Is this a result of the governor? If so, why is it that I loose about 200 RPM when I put a discharged battery bank online? Am I under-propped?


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## ebs001 (May 8, 2006)

Sailboy, if you're asking why you loose RPMs when you are charging your batteries the answer is that it takes energy to operate your alternator especially a high output one operating in the bulk phase. In my experience the rpms are reached more slowly than you suggest and so a boat at 0 velocity is not reving at the same rate as it is when it is doing 5 knots. The difference between say 3 and 5 are negligible when reading an anologue tach. Are you under propped? If you don't want to test the max on your engine than you'll have to go to the manufacturer's specs to find out.


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