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Old 05-07-2010, 16:27   #1
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RPMs for Yanmar 3gm30

I was reading somewhere that a yanmar 3gm30 is a high rpm motor max rpm 3500 and cruising 3000. The article said that anything below that is doing mor damage than good with carbon deposits etc....is what I read true or is this just not the case.
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Old 05-07-2010, 16:44   #2
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No idea but my cummins low rpm to hp is why it sits in my engine room. No turbo not fancy but it starts in a moment. U can't say more for TAD and the cummins repowet I did. I don't want to know about 3200 rpm turbo engines. I sail and sometimes motor sail occasionaly motor off the hook. For that kinda sailng the cummins is very good. Why a yanmar?
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Old 05-07-2010, 17:15   #3
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I have 1000 hours on my Yanmar 3gm30f.
I run it at 2750rpm cruising. I will occasionally run it up to 3000rpm for 5 minutes (every couple of hours or so). Every once in a while I will run it up to the stops 3500rpm for a minute or so just to blow it out.
The engine runs perfectly.
At 2750rpm I burn 1/2 gph at 6.5knots. At 3000rpm I burn 3/4 gph at 7 knots.
It really depends on your boat/prop. As long as the engine is "working" and running at temperature I wouldn't worry too much about strictly being at 80% rated output.
The real killer is letting the engine run at low rpm in neutral while at anchor to charge batteries. I don't do that ever. I have solar charging.
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Old 05-07-2010, 17:17   #4
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I've run my 3GM30F for years (not continuously ) at about 2500 rpm, still going strong.
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Old 05-07-2010, 18:06   #5
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We cruised with such twins and as far as I remember we were at 2400-2500 when on one engine and about 2100 when both.

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Old 05-07-2010, 19:13   #6
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The 3gm30f has a 3850rpm redline, 3600rpm one hour rating, and 3400rpm continuous.

I run mine at 2700-2800rpm as this is the best fuel consumption to torque rating.
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Old 05-07-2010, 20:15   #7
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Happy speed for Yanmar 3gm30

Quote:
Originally Posted by irwin28 View Post
I was reading somewhere that a yanmar 3gm30 is a high rpm motor max rpm 3500 and cruising 3000. The article said that anything below that is doing mor damage than good with carbon deposits etc....is what I read true or is this just not the case.
There is a speed where most diesel engines sound "happy". I find that for constant RPM use (like in a boat) it is usually half way between maximum torque and maximum RPM. I'm not totally confident in the figures I have found, but what I've got says the 3GM30 develops maximum torque at 2600 RPM and maximum power at 3600 RPM. The middle of this is 3100 RPM and that's what I'd regard as my cruising RPM. I don't like to push an engine past where it "sounds" happy. If I was not in a hurry, I would not be concerned about running it much slower provided that you revved it out to at least the 3100 occasionally. At lower revs you will save a fortune in fuel and this will more than compensate for an engine rebuild a little bit earlier than otherwise. Much of what is said about bore glazing is more applicable to older two stroke diesels (eg Detroit Diesels) and I think is not the same concern for a modern 4 stroke.

I expect that there will now be many posts disagreeing with me, but my opinions are based on my real life experience as a diesel mechanic and a bus company owner with many diesels and 1 Yanmar engine in my little sailboat.

Greg
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Old 06-07-2010, 06:00   #8
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See the Yanmar Engine Operating Guidelines
Yanmar Marine Engine Help

yanmarhelp.com/operate.htm
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Old 06-07-2010, 06:54   #9
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Like others have said earlier, we have been running our 3GM between 2500 and 2750 for cruising. Occasionally higher (but it really sucks fuel). No problems. Ten years old now and nearly 800 hours.
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Old 06-07-2010, 07:19   #10
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Gords link is a good short read. Diesels like to be run to last. Yanmar will tell you that offsetting lower rpm operation by running it up to rated rpm for ten minutes or so will reduce the possibility of glazing. There's a happy medium between over working a diesel and operating it at too low an rpm to save fuel all the while trying to make your engine last. Killing your engine with kindness is not always a myth. Diesels can easily run at a much higher rpms than they are set for. Yanmar does not set their governors 300rpms faster than your engine can handle.
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Old 06-07-2010, 08:00   #11
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Some hints based on Diesel engine designers and operators suggestions. Maximum torque is usually the best RPM to operate an internal combustion engine for long periods as this is the point at which it is most efficient. Remember though prop mismatch can alter this figure in individual cases but if I was setting up a motor and prop I would be aiming to cruise at or just below max torque RPM. Use a mono grade oil as this will lessen the likelihood of bore glaze. Yanmar recommend mono but do not push the point and usually will give the okay to multi grade. Mono grade is used in most stationary engines and a boat motor operates for long periods at set RPM just like a stationary engine. Turbo charged engines are much more likely to glaze bores hence Yanmar are only fitting the AC power generators to there non turbo range of boat engines as they are the ones that will be run in neutral with light load for extended periods. The other unwritten rule is change your oil often it is cheap in comparison with an engine rebuild. Most will go to great lengths to provide clean fuel but neglect the oil. I am sure that many will say they have done all the no no's listed but that does not mean its correct. At the end of the day you are likely to save money by following these simple guidelines.
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Old 06-07-2010, 11:27   #12
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Quote:
Originally Posted by meyermm View Post
Some hints based on Diesel engine designers and operators suggestions. Maximum torque is usually the best RPM to operate an internal combustion engine for long periods as this is the point at which it is most efficient. Remember though prop mismatch can alter this figure in individual cases but if I was setting up a motor and prop I would be aiming to cruise at or just below max torque RPM. Use a mono grade oil as this will lessen the likelihood of bore glaze. Yanmar recommend mono but do not push the point and usually will give the okay to multi grade. Mono grade is used in most stationary engines and a boat motor operates for long periods at set RPM just like a stationary engine. Turbo charged engines are much more likely to glaze bores hence Yanmar are only fitting the AC power generators to there non turbo range of boat engines as they are the ones that will be run in neutral with light load for extended periods. The other unwritten rule is change your oil often it is cheap in comparison with an engine rebuild. Most will go to great lengths to provide clean fuel but neglect the oil. I am sure that many will say they have done all the no no's listed but that does not mean its correct. At the end of the day you are likely to save money by following these simple guidelines.

Explain to me the multigrade vs mono...and why one is more likely to glaze.
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Old 06-07-2010, 12:01   #13
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Quote:
Originally Posted by meyermm View Post
... Use a mono grade oil as this will lessen the likelihood of bore glaze. Yanmar recommend mono but do not push the point and usually will give the okay to multi grade. Mono grade is used in most stationary engines and a boat motor operates for long periods at set RPM just like a stationary engine...
I too would appreciate an explanation.

Mono-grade oil viscosity designations describe the fluidity of the oil at 100 degrees Centigrade - with higher numbers corresponding to thicker oils.

Multi-grade engine oils combine the benefits of remaining fluid at low temperatures, but retaining adequate thickness to protect the engine at operating temperatures. The high temperature viscosity at 100 C is described in the same way as for mono-grade engine oils. Thus an SAE 15W-40 oil has the same thickness as an SAE 40 mono-grade at 100 C, however, remains fluid and pumpable down to -15 C. An SAE 40 mono-grade may become excessively thick at these lower temperatures.

Multi-grade oils tend to be of significantly higher quality than mono-grade oils. Indeed, it is impossible to pass many of the latest high performance diesel engine tests (eg those in API CG-4, CH-4, ACEA E3, E5 etc) with mono-grade oils.
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Old 06-07-2010, 12:18   #14
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We have a Yanmar 4JH3-HTE, four-cylinder, turbocharged and intercooled, 2000cc, 100 hp engine.

Redline is 3800 (!) and continuous is 3600. 3000rpm is the fastest I will run it for any length of time; it does not sound or feel comfortable above that. The boat will reach hull speed at about 2800 in reasonably calm water so there's hardly any reason to do so anyway.

My usual cruising RPM is 2400rpm so long as I'm not fighting a tide or in a hurry; otherwise 2500 up to maybe 2700.

Fuel consumption goes up apparently geometrically with RPM, so that's another incentive to keep the revs down. It must be said that we have a Bruton self-feathering prop which milks every last drop of power out of the engine at reduced rpms, making it more efficient. But the difference in fuel consumption is amazing; I guess 4 liters/hour at 2500 and 10 liters/hour at 3000; something like that.

I don't know if it's good for the engine to run it at 2400 but it sounds and feels right. The recommended speed of 2900 from here Yanmar Marine Engine Help is just not right, at least not for our boat and prop.
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Old 06-07-2010, 12:34   #15
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I dont know what the difference in the single vrs muti oil are but on my first trip down the icw about 200 hrs with a 40 weight oil I used about 3 quarts the whole trip The following year with the same brand oil except 10w 40 i used 0 quarts of oil so I am a believer
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