Why run high rpm's with a diesel ?

miketrock

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Nov 25, 2019
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15
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Pa
At first I thought it was odd that people here were being told to run their tractors most of the time at full rpm's when doing work. To me, a diesel is a low rpm torquer. Then it occurred to me that most of the tractors in discussion here are small NON-TURBO engines. That's it, I'm used to all diesels being turbo charged: pick ups, tractor trailers, construction equip. And I noticed on this forum and youtube videos that the hydraulic transmissions will get too hot if you work them hard at low rpm's with low volume flow of the hydro tranny fluid, that higher flow rate allows better cooling of the fluid while operating. Somebody (I think in a video by Tractor Mike) said its better to be in a lower gear (range) and higher rpm's than a higher range and low rpm's while working the tractor hard. Makes sense now, knowing that the hydro fluid and tranny can overheat and in time and kill it or wear it out prematurely.
 

Redlands

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Sep 16, 2016
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North Central Oklahoma
Also many of them are designed to provide the best power range at a higher RPM. Low RPM really lugs the engines not to mention the hydraulic fluid flow rates, psi, heating issues.
 

nbryan

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Equipment
B2650 BH77 LA534 54" ssqa Forks B2782B BB1560 Woods M5-4 MaxxHaul 50039
Jan 3, 2019
833
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Hadashville, Manitoba, Canada
If by high rpm you mean rated rpm, I always run my B2650 at rated 2500 rpm when driving a pto driven attachment like my chipper or snowblower, and for my backhoe.
I also bump it up there when I have consistently heavy loader or pulling work, or for booting it down the road.
Most of my regular light duty operations like shuttling a few buckets of firewood or compost around, fork-lifting moderate loads, getting A-B with a trailer, I run between 1800 - 2200 RPM. Any work that starts to make the engine lose too many rpm I bump it up again.
My thought is throttling back from full rated engine rpm by a few hundred rpm for non-heavy workloads is not stressful for the engine or hydraulic systems, and reduces noise and fuel consumption.
But as soon as there's a pto attachment or the backhoe, it's full 2500 rpm.
 

i7win7

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Anything over 26HP has to have pollution control systems. Running fast and hot reduces soot buildup in particulate filters and reduces the amount of regen cycles to keep exhaust flowing. If system won't regen, filters have to be heat treated in high temp ovens or more expensive REPLACED. I have 2 - 26HP machines and run them between 2000 and 2200 rpm. Run at max only when max power is needed.
 

NHSleddog

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B2650
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I wish the throttle was tied to my actions. Putting around the yard at full RPM is just wasteful to me. It would be a lot better if the governor could adjust for needed load.

If it will overheat due to low RPM how long will that take? So the tractor idling out in the yard after "x" will overheat? That seems odd and I don't remember reading it in the owners manual.
 
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mikester

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If you have a DPF system hotter engines work better and will have less issues. If you dont have the pollution control junk then run the engine speed to match your work.
 

RLinNH

Member

Equipment
B2650,LA534,BH77
Mar 10, 2018
59
1
6
NH
I wish the throttle was tied to my actions. Putting around the yard at full RPM is just wasteful to me. It would be a lot better if the governor could adjust for needed load.

If it will overheat due to low RPM how long will that take? So the tractor idling out in the yard after "x" will overheat? That seems odd and I don't remember reading it in the owners manual.
No, idling out in the yard in "Northern Massachusetts", your tractor should not over heat. I like to let mine idle for at least 20 minutes when I first start it up in order to let everything get up to temp.
 

dirtydeed

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I wish the throttle was tied to my actions. Putting around the yard at full RPM is just wasteful to me. It would be a lot better if the governor could adjust for needed load.
Seems like there are some manufacture/models that have "auto throttle". That would be a handy feature to have, for me at least.
 

SDT

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multiple and various
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If you have a DPF system hotter engines work better and will have less issues. If you dont have the pollution control junk then run the engine speed to match your work.
Bingo.

Ignoring nonsensical emissions equipment, there is no need to operate a diesel engine at rated engine RPM when such power is not needed. Nor is there any significant advantage of doing so. Moreover, operating at rated engine RPM when such is not necessary runs up revolutions (hours).

Until the introduction of emissions equipment, the belief that diesel engines should always be operated at high (rated) RPM was largely an unjustified myth.

Yes, I am well aware of the wet stacking argument but such is of little concern if, as is just about everything else, not taken to extremes.

SDT
 

SDT

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Seems like there are some manufacture/models that have "auto throttle". That would be a handy feature to have, for me at least.
Kubota has so-called auto throttle advance on HST+ models.

SDT
 

troverman

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MX6000 HSTC; 2020 Kubota Z421KW-54 zero turn mower
Jun 9, 2015
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NH
If you want max power for PTO driven implements, use wide open throttle. If you are doing loader work, or some other non-PTO function, than use less throttle. The advantages of less throttle are many: less fuel consumed, less noise, less jerky / sensitive controls.

Turbo vs non turbo really has nothing to do with it - there are plenty of turbo Kubota tractors out there, in both the Grand L and MX series on the smaller side.

Regarding emissions, a general consideration is that tractors running at wide open will probably have longer intervals between required DPF regens and this ultimately means the DPF lasts longer and less fuel/oil dilution occurs. However, in reality, whether you have a lot or only a few regens most users will never wear out a DPF.

I have a Grand L and it does offer the linked throttle which is nice...you can switch it on or off.
 

NHSleddog

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B2650
Dec 19, 2019
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re: It would be a lot better if the governor could adjust for needed load.

A govenor DOES adjust for the load... at least every guv on every tractor or truck I've ever had...
Yes, I know that. I don't think you understand what I mean.

I don't want to run the throttle high all the time. I don't even want to run past 2K when puttering around.

As others have posted, it looks like Kubota has something like what I am talking about. Similar to the treadle (sp?) pedal acting like an accelerator.
 

GreensvilleJay

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BX23-S
Apr 2, 2019
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re: Similar to the treadle (sp?) pedal acting like an accelerator.

That was an option on my A-C D-14s and was going to add one (easy...have diagrams...) but property is small enough not to warrant the time to fab it up.
After 20 years of running D-14s , I'm used to the throttle quadrant lever.

If Kub offered it for a similar tractor/series you may be able to buy the 'kit' of parts needed for yours
 

miketrock

Member
Nov 25, 2019
160
15
18
Pa
I wish the throttle was tied to my actions. Putting around the yard at full RPM is just wasteful to me. It would be a lot better if the governor could adjust for needed load.

If it will overheat due to low RPM how long will that take? So the tractor idling out in the yard after "x" will overheat? That seems odd and I don't remember reading it in the owners manual.
No, not the engine overheating just sitting in the yard idling, that isn't what I said. The hydro tranny can overheat if you run the tractor under heavy load in a higher gear (or range) with lower engine rpm's. Instead, it's better to use a lower gear (or range) of the tranny and higher engine rpm's so that you have higher hydro fluid volume moving to provide better cooling for the hydro fluid and tranny. Apparently, the main reason for higher rpm's is more for the hydraulic transmission not the engine.