proper operating RPM

[ad356]

i have a friend of mine that insist that if i run my tractor at less then rated rpm, lower rpm=longer engine life. he suggests that i mow at 2,400-2,500 rpm, the tractor seems to handle the load just fine at those RPM's. what is the general consensus here in regards to maximizing engine life and best fuel economy? why does it seem like the maximum rated RPM is so much higher then the other sub compact diesels on the market. the maximum rated RPM for this engine is 3,200; which just seems like a very high RPM for diesel engine. my tractor only has 400 hours on it (bought used). that's a pretty low time engine and i am hoping for many thousands of hours.

what's the typical engine life of a well maintained D902?

 

[BruceP]

I do not have specific answer for you but I do know there is a specific engine RPM for each:
1)Max economy
2)Max torque
3)Max HP
4)longest engine life

The first 3 are relativity easy to ascertain while #4 may not be easy to determine.

Also understand that the hydraulic pump has some ratings too.
If it is spun too slow or too fast, then its life can be compromised....not to mention losing efficiency.

Personally, I try to spin the engine at the RPM which the hydraulic pump is rated for max efficiency.

 

[chim]

I haven't paid much attention to engine RPM's on my current tractor. The performance of the mower takes priority for me. A nice cut and distribution of clippings is mainly what I watch for. The RPM's required for that vary with the grass length and juiciness. Right now that means running the PTO at around 400 RPM's.

 

[85Hokie]

Bruce said it perfectly....but I'll add to it

I'll tell you this - you cannot run it too high, Kubota DESIGNED it to run at "X" rpm. That is not just a random rpm range that the throttle stops on. So what many are saying when running the machine lower than they "need to" is that they know MORE about the engine design and hydraulic pump specifications than the engineers that creating them.

If you look at most diesel operated pieces of equipment, like compressors, welders, or generators ....they run at "X" rpm, there is no "lowers" setting. Why - because that is what the machine performs well at and designed to do.

Professional operators....hoes, FEL and dozers are not putting around at 70% throttle, they know better!

I find that my BX and B's run fine at 70% of rated RPM, but it still runs and performs much better at 90-100% rpms.

I'll tell you this - run it where it is designed to run...change the fluids often and IT WILL LAST damn near forever....

Run it at a lower rpm and think you are helping the situation and you will soon see after a couple of 100 hours.....something is amiss.

My BX works very well at 3000 - 32000...it almost sings...my B's are singing at about 2600 rpms....and both have different WOT settings.

Your machine - do as you think is best.

 

[conropl]

All the above. They are designed to be able to run WOT.
I assume you are talking about a MMM. My dealer told me to run the mower at full throttle, and I never had an issue.

Now the argument against reduced throttle: You always hear the argument that increased RPM's adds more cycles to the engine and will reduce life. But that is not necessarily a correct statement. If you reduce the throttle (and consequently RPM's) and you run into a situation that causes the engine to "lug" (reduce RPM's further), then you are doing more harm than good. That short period of time the engine was lugging caused more harm to your engine than if you had run it at WOT without lugging the engine. The point being... it is less likely to lug (detrimental to engine) at WOT than if you had reduced throttle/RPM's. Keep the RPM's up and you will have less issues with insufficient power... which is better cosidering the long view of engine life.

As an extreme example, my brothers neighbor has several pieces of diesel equipment. It is his hobby - he likes to work on them. But he keeps running them at idle thinking he is saving the engine life. So he is out working his skid steer at idle and he keeps over loading it and stalling the engine. For some reason he has got it in his head that what he doing is better for the engine than increasing the throttle. So he is constantly lugging the engine, and it gets to the point that he stalls out the engine several times when using it. That is hard on the engine, but he has less cycles on it... makes no sense.

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[SidecarFlip]

In my view I look at the torque and horsepower curve for my particular engines and I run them at the peak of the torque curve which isn't peak horsepower. diesel's have what is called 'torque rise' and I run mine at the peak of torque rise which is also the most efficient fuel usage point as well.

In as much as mine are turbocharged, that is also where maximum boost is at too.

 

[SidecarFlip]

Just as a point of operating parameters, I just added a 2 speed PTO to my cab M9. I did it because there is no point in running the engine at rated PTO (540) rpm, which is 2300 rpm.

I produce maximum torque around 1600 rpm so in the interest of fuel economy (my tractors use a bit more fuel than a small one), I added the 540-1000 pto and now I can run the 1000 rpm pto (with a 21 to 6 spline adapter) at 1600 rpm and take advantage of fuel economy and longer engine life and at 1600 rpm the power produced will operate all my implements and it's certainly not lugging the motor.

I see the newer larger Kubota's now come with a 540E setting on the pto. The E setting is the 'economy' setting which gives you more fuel efficiency but still provides the necessary torque to rum implements.

Just my view of operating parameters.

 

[Tornado]

as a novice tractor owner I have read a lot on this topic as I was curious about this as well. All the reading and research I have done has suggested to me that you are better off to run at higher RPM's rather than lower RPM's. One reason that I dont think has been mentioned here yet, but that Ive found several places in my research, is that when the RPM is higher you are circulating more oil volume through the engine. If you operate at low RPM's and strain the tractor you are getting less oil circulation, more strain, more friction, and more heat, all bad things.

Given my research on the issue I have chosen to operate my new L2501 in the following way: Most work I do in low gear, and higher engine RPM's. Rather than Medium gear and lower RPM's. If I need more speed I bury the HST pedal while staying in low gear for most of my working. Ive read that this is the preferred way to operate an HST for muc hte same reason - More circulation of oils and lubricants than if you run in medium gear and just barely engaging the hst. Sometimes you need to operate in Medium gear cause you just dont have the speed in low, and thats understandable. Everything I have read though has suggested to me to run at the highest rpm you can. When mowing, run at rated mower pto speed, or some say a touch higher.

Lastly, With my L2501 being at just 10 hours operation right now, I have avoided running my tractor at full throttle, as the manual states to not run at full throttle for the first 50 hours of the machines life. I get the theory behind why, and I know some dispute it. To be onthe safe side however ive elected to simply follow the manuals instruction on this. The L2501 maxes out rpm at around 2400 if I remember right.. 540 pto speed is around 2100, so youre running at near full throttle on an L2501 at the 540 pto speed. Ive kinda set 2100 as my top end for now, and tend to stay around 1900 or 2000 when working for now. After 50 hours and my first maintenance, I will start opening it up more.

 

[D2Cat]

ad356, you say, "...and i am hoping for many thousands of hours."

Average homeowner use of a tractor is in the neighborhood of 50 hours per year. So if your tractor is mistreated, un-attended service wise. and throws a rod at three thousand hours....that will take 60 years.

I've seen Kubota diesels with over 10K hours on them. Obviously they use them much more than 50 hours a year.

I trust you will guide yourself accordingly!!

 

[SDT]

i have a friend of mine that insist that if i run my tractor at less then rated rpm, lower rpm=longer engine life. he suggests that i mow at 2,400-2,500 rpm, the tractor seems to handle the load just fine at those RPM's. what is the general consensus here in regards to maximizing engine life and best fuel economy? why does it seem like the maximum rated RPM is so much higher then the other sub compact diesels on the market. the maximum rated RPM for this engine is 3,200; which just seems like a very high RPM for diesel engine. my tractor only has 400 hours on it (bought used). that's a pretty low time engine and i am hoping for many thousands of hours.

what's the typical engine life of a well maintained D902?

With the exception of my L6060,I rarely (almost never) operate any of my tractor engines at rated speed.

Wear is a function of revolutions. More revolutions=more wear and more "hours" on a mechanical hour meter, which is not an hour meter at all bur a revolution counter.

SDT

 

[Freeheeler]

With the exception of my L6060,I rarely (almost never) operate any of my tractor engines at rated speed.

Wear is a function of revolutions. More revolutions=more wear and more "hours" on a mechanical hour meter, which is not an hour meter at all bur a revolution counter.

SDT

However, all revolutions are not equal, otherwise you'd always run everything at idle. Revolutions at stress (think lugging the engine under power) cause a lot more wear and tear than unstressed revs (doing the same chore at a higher rpm that does not lug the engine). Adjusting the rpms to the match the engines torque to the chore being done keeps the wear level at a constant rate, making scheduled maintenance time related vs rotation related. That's why they have hour meters vs revolution counters. Neither is a perfect accounting of stress on the engine, but for the average user, hours is a better indicator than revolutions if run in the appropriate rpm range.

 

[SidecarFlip]

With the exception of my L6060,I rarely (almost never) operate any of my tractor engines at rated speed.

Wear is a function of revolutions. More revolutions=more wear and more "hours" on a mechanical hour meter, which is not an hour meter at all bur a revolution counter.

SDT

Exactly, the faster it spins the faster it wears. Oil pressure and flow is nly dependent on rpm up to a certain point, usually well below maximum rpm. Once the pressure is established the bypass will control the total flow anyway.

 

[SidecarFlip]

If a JD 4020 Diesel can go 200K hours with just routine maintenance, A k ubota should be able to as well.

Don't see even 50K hours accruing on a Kubita residential tractor.

 

[conropl]

We are talking about mowing with BX tractor. That is a high torque operation for that tractor. If he sets his throttle to get optimum torque (rpm's at peak of torque curve) while there is very little load applied, then when his tractor does load up when he gets into grass (or pushes his loader into a pile of dirt) he is not going to have enough fuel supplied to maintain that RPM. He immediately drops RPM's and torque. So a load will cause a drop in RPM's and torque and with escalate into lugging faster. If the throttle is at full (RPM's past the peak of the torque curve), then as he loads up the tractor it will reduce the RPM's to bring you into the peak torque range and you have enough fuel being supplied to hold you there until the tractor recovers from the load. Never lugs or at least gives you a chance to react to the higher load... more better.

The comment about the number of hours is legitimate as far as number of cycles goes. Then the only good reason to reduce RPM's is for fuel consumption, but that is not really a big factor with a BX.

I am not trying to come off as an expert... because I am not. Just trying to put some logic into what is going on to justify it in my own mind. Basically, it does not seem right to me to be at peak torque without enough throttle to hold you there if the load goes up. I would also rather have the torque go up as I load it up and RPM's drop a little instead of drop off the peak as load is applied because you do not have enough throttle to hold you there.

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[troverman]

It's pointless to be concerned about "wearing out" your tractor prematurely based upon engine speed. It just isn't going to happen.

 

[SDT]

However, all revolutions are not equal, otherwise you'd always run everything at idle. Revolutions at stress (think lugging the engine under power) cause a lot more wear and tear than unstressed revs (doing the same chore at a higher rpm that does not lug the engine). Adjusting the rpms to the match the engines torque to the chore being done keeps the wear level at a constant rate, making scheduled maintenance time related vs rotation related. That's why they have hour meters vs revolution counters. Neither is a perfect accounting of stress on the engine, but for the average user, hours is a better indicator than revolutions if run in the appropriate rpm range.

Agreed, but revolutions are revolutions. No revolutions=no wear.

Additionally, but for newer electronic instruments, nearly all so called hour meters are actually revolution counters. Most are designed such that one "hour" approximates 60 minutes at rated engine RPM. This is why so called "hours" accumulate more slowly at lower engine RPM than at higher engine RPM with such meters.

SDT

 

[bucktail]

If a JD 4020 Diesel can go 200K hours with just routine maintenance, A k ubota should be able to as well.

Don't see even 50K hours accruing on a Kubita residential tractor.

The JD 404 is a good engine but they don't go 200,000 hours between overhauls. More like 10000to 15000.

 

[beex]

Always in these RPM discussions there is the theory proposed that the engine is designed to run at X rpm, which is the speed for 540 pto speed, and that is the RPM you should always run at.

I’m not buying that. As far as I can tell after running tractors for 45 years is that tractors are designed to have peak HP at the RPMs where you get the standard the 540 rpm on the PTO. This will give you peak performance such as using the MMM, and lots of other stuff. And the tractor is designed to run at this speed as much as the operator wants with no damage or excessive wear. This is not no wear and not minimal wear, it is acceptable wear to get acceptable tractor life.


But. 1) the engine is actually designed to run at a range of RPMs with no problem. 2) it’s vey rarely you need max performance, 3) minimum wear will be at a lower RPM, given your not lugging. Lugging puts excessive torque in the system, which is wear.

On my bx, when using the MMM i run at the speed where I get sufficient performance for the conditions and not close to lugging. High wet spring grass , 2800-3000. Dry thin summer grass 2500. Loader operating, don’t need much power at all, 1900-2000 is all i need, driving around, 1800.

And my manual says, don’t run excessive RPMs for the task.

Max performance is going to be designed close to WOT because it doesn’t make sense to run a higher RPMs where the torq drops off so fast the HP goes down above that speed, and that is more wear for no benefit.

But I would bet a lot of money that if you tested scientifically, you would find any RPM less than WOT that gets the job done is less wear as long as your not lugging. The motor needs to turning smoothly, no smoke.

That said, I’m not saying you shouldn’t run WOT if you want the performance, sometimes the extra performance is worth cost of acceptably more wear.



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[SDT]

The JD 404 is a good engine but they don't go 200,000 hours between overhauls. More like 10000to 15000.

Bingo, Bucktail.

Most are overhauled around 10k.

SDT

 

[SDT]

Always in these RPM discussions there is the theory proposed that the engine is designed to run at X rpm, which is the speed for 540 pto speed, and that is the RPM you should always run at.

I***8217;m not buying that. As far as I can tell after running tractors for 45 years is that tractors are designed to have peak HP at the RPMs where you get the standard the 540 rpm on the PTO. This will give you peak performance such as using the MMM, and lots of other stuff. And the tractor is designed to run at this speed as much as the operator wants with no damage or excessive wear. This is not no wear and not minimal wear, it is acceptable wear to get acceptable tractor life.


But. 1) the engine is actually designed to run at a range of RPMs with no problem. 2) it***8217;s vey rarely you need max performance, 3) minimum wear will be at a lower RPM, given your not lugging. Lugging puts excessive torque in the system, which is wear.

On my bx, when using the MMM i run at the speed where I get sufficient performance for the conditions and not close to lugging. High wet spring grass , 2800-3000. Dry thin summer grass 2500. Loader operating, don***8217;t need much power at all, 1900-2000 is all i need, driving around, 1800.

And my manual says, don***8217;t run excessive RPMs for the task.

Max performance is going to be designed close to WOT because it doesn***8217;t make sense to run a higher RPMs where the torq drops off so fast the HP goes down above that speed, and that is more wear for no benefit.

But I would bet a lot of money that if you tested scientifically, you would find any RPM less than WOT that gets the job done is less wear as long as your not lugging. The motor needs to turning smoothly, no smoke.

That said, I***8217;m not saying you shouldn***8217;t run WOT if you want the performance, sometimes the extra performance is worth cost of acceptably more wear.



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Well said, BEEX.

The best argument for operating at rated speed when mowing with a finish mower is to produce high blade tip speed and increased vacuum. Both improve quality of cut, especially in heavy or tall grass.

I installed high vacuum blades on my B1750HST MMM and usually mow at 2,000 RPM. Been doing so since 1993.

SDT