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Diesel RPM

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MikeC
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2000-08-18          18964

I'm looking for some feedback on what's the best practice for selecting operating RPM in order to maximize engine life. I have a JD855 which has a range of 1400 to 3425 RPM. Is it always best to run the machine at the lowest RPM which does the job effectively? It seems from some posts here that some of the longest living farm tractors have a max RPM thats not far from my minimum RPM! I can get most tasks done in the range of 1800-2500 RPM, and have rarely had it above 3K. Does anyone else feel that it's worth being judicious with RPM so that your machine will last longer, or will it not make much difference assuming you maintain it properly? Also, should I be concerned about carbon buildup if I run it too long near idle? This is modern (1996 Yanmar) diesel with direct injection. It seems that they'd be able to design-out problems like this by now. Comments appreciated.

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Jack in IL
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2000-08-18          18965

Mike, I think you are being overly cautious. Proper maintanence and keeping the filters clean will most likely have the greatest effect on engine life. For PTO equipment such as mowers, you do need to keep the engine at the RPM that corresponds to 540 at the PTO (there is a yellow mark on your tach). If you run the engine slower, the blade tip speed may not be high enough to give a clean cut. For loader work, you need enough engine speed to allow the hydraulics to work with ease and respond quickly. ....

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Larry in MI.
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2000-08-18          18967

I have a JD4100 that had injector problems. One of the first questions my dealer asked me is "are you sure you have been running it wide open?" Wide open is in the neighborhood of 2750 rpm on the the JD4100. Wide open is the setting to use for mowing grass and almost wide open is the setting to use with 540 rpm 3 pt. hitch attachments. The dealer said that anything much less than full throttle does not generate enough heat in the smaller diesel engines to keep the injectors clean. I don't know if any of this is true but it is what my dealer told me. ....

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Roger L.
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2000-08-18          18971

I agree with Jack....you may be overly cautious. I don't think that anything that you are worrying about will affect its life one way or the other. In fact, it wouldn't surprise me at all if that engine outlasts your desire to keep it - and does so without any noticeable wear. If you are curious, search the messages on this tractor board - they are all archived - and I think that you will find that engine wear is rarely discussed. My little compact has almost 20 years of hard use with normal attention to routine maintenance. About the only thing I do special is to warm it up well in cold weather. As far as I can tell, the engine hasn't aged at all.
I run it at whatever engine speed seems to make it (and me) happy. Even though the book says that the engine is designed to be run at 2850, I find that I run in the 1500 rpm range most of the time. My normal operating speed is at idle most of the time interspersed with bursts of full throttle when I am using the loader or traveling between piles of dirt and the job to be done. So the tractor gets a lot of time at idle with the "cobs" blown out of it for short runs. I have never had a problem with carbon buildup...and am toying with the idea that carbon is not as likely to be a problem with a direct injected diesel anyway.

....

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Art White
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2000-08-19          18976

You could be loosing some of the engine life if you are not building enough temperature inside the engine to properly burn the fuel. This often happens with my farm customers during the winter or if the thermostat goes bad. The end result is glazing of the cylinder walls and loss of horsepower. Mowers are meant to be run at full throttle or pto speed but the grass you don't cut may be acceptable to you. Your engine should last with good care in excess of 10,000 hours so your only worry should be what family members are going to fight over it when you are gone. To Rogers shogrin indirect injection burns cleaner than direct it's just more expensive to build. ....

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Roger L.
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2000-08-19          18977

Yep, I agree with you Art...the indirect injection generally burns cleaner than the direct injection. It would hardly be otherwise since indirect gives you that nice precombustion chamber to get the ignition going. What i'm saying is that if you run at LOW RPM you will unavoidably build up some carbon. And if you do that, you will have a chance of building some carbon in some of those little ports leading to and from the indirect chamber. I've seen that happen. So for running at less than rated RPM I am speculating that a direct injection might be better. ....

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MikeC
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2000-08-19          18988

So I may actually be doing more harm than good running it at low RPMs. So much for good intentions! Thanks all for the good feedback. Would a temperature gauge be worth while for cold weather warm up and to make sure your thermostat id still working? ....

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Roger L.
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2000-08-20          19002

Yes, probably more harm than good....with the caveat that it isn't enough more harm to ever make an difference!
Yes to the temperature gauge idea as well. I removed my idiot light sender and screwed a "T" fitting into its place in the block. Then screwed the I.O. sender into one side of the T and a sender for a temperature gauge (capillary tube type) into the other side of the T. Now the tractor has warning light and gauge both. I used a cheap universal gauge and it is very nice and accurate - I checked it against a laboratory gauge before installing. :-) Total cost was under twenty-five bucks. ....

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MikeC
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2000-08-20          19016

Sounds good. Inexpensive, and easy to install. Now I've just got to find a place to mount the guage. Maybe there's an un-used guage knockout in the dashboard. Time to got out to the garage and look... ....

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Greg Harrison
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2000-08-21          19018

The book that came with my L4310 Kubota advised not to run rpm's above that needed to do the job. I would suppose that meant no lugging. Just use common sense, if the weeds are small don't use wide open throttle. Use enough rpm to do the job and not lose more that 1-200 rpm on the heavier spots. Sounds as though you already have it figured out.
Happy tractoring
Greg H ....

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Roger L.
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2000-08-21          19021

Greg, it's nice to see Kubota recommending that people use their tractors in the way that lots of us prefer to do. I don't think that I've ever read my owner's manual that closely. I'll have to look at it to see "exactly" how they word the section on recommended RPM.
Anyone wanting to add oil and temperature gauges with a "T" connector be sure to check to see if the block is tapped metric, US machine thread, or tapered pipe thread. I've seen them all ways. Automotive stores are the best sources I've found for the brass "T" as well as the gauges. Having tried several different gauge sets, my favorite (and the most accurate) is a subminiature set of three gauges in it's own mount for bolting under the dash of a car. I bolted mine similarly - under the sheetmetal just in front of the gearshift. The temperature is a capillary tube type, the oil pressure is an oil-filled nylon tube, and the other is amps. I have nothing against the electrical sender type for warning lights, but was looking for long-term repeatability on the analog gauges and decided to go with "real" gauges i.e.. The gauges were very cheap...in the $20 to $30 dollar range for the set!
....

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Brad Sauter
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2000-08-29          19245

Run it open. Diesels need the heat and low rpms for extended times can hurt. The fuel will not burn completely and was down the cylinder walls. This is why I also have an idle controller in my diesel pickup so when I idle for more than ten minutes say with the A/C or heat on I bump my idle up to 1200rpm from 680 normal idle to help combustion and maintain engine life. ....

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