Max Cruising RPMs for Yanmar - Page 2 - SailNet Community
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post #11 of 36 Old 04-08-2008
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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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post #12 of 36 Old 04-09-2008
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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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post #13 of 36 Old 04-09-2008
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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.

beej67, Checkered Past, 1980 32' Pearson 323, Panama City FL

Last edited by beej67; 04-09-2008 at 10:07 AM.
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post #14 of 36 Old 04-09-2008
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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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post #15 of 36 Old 04-09-2008
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Jason,

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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.

s/v Libertine
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post #16 of 36 Old 04-09-2008
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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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post #17 of 36 Old 04-09-2008
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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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post #18 of 36 Old 04-09-2008
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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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post #19 of 36 Old 04-09-2008
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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

-- Jody

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post #20 of 36 Old 04-09-2008
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Quote:
Originally Posted by petegingras View Post

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.

Hud
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