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Kubota Hydrostat - what range? #4457315
07/12/17 01:17 PM
07/12/17 01:17 PM
Joined: Apr 2016
Posts: 1,198
Campbellsville, KY
Alex_V Offline OP
Alex_V  Offline OP
Joined: Apr 2016
Posts: 1,198
Campbellsville, KY
I regularly operate several pieces of Kubota equipment with hydrostatic transmissions. In a system such as this, which puts the fluid under more stress at the same ground speed: wide open pedal in low range, or, say, 1/3 pedal in high range?


To quote a friend, "Synthetics, man."

'85 GMC C3500, 454, 132K
'82 Mercedes 300CD, OM617 turbo, 173K (totaled 2018, in rehab)
'85 Mercedes 300TD, OM617 turbo, 217K (wife's)
'67 Suburban, 350, 331K
Re: Kubota Hydrostat - what range? [Re: Alex_V] #4457332
07/12/17 01:41 PM
07/12/17 01:41 PM
Joined: Aug 2003
Posts: 13,137
NE,Ohio
Rand Offline
Rand  Offline
Joined: Aug 2003
Posts: 13,137
NE,Ohio
I wouldnt be worrying about "stress" on the hydraulic fluid.


2019 Jeep Cherokee Trailhawk 2.0T
Re: Kubota Hydrostat - what range? [Re: Alex_V] #4457365
07/12/17 02:11 PM
07/12/17 02:11 PM
Joined: Sep 2013
Posts: 10,679
Indiana
dlundblad Offline
dlundblad  Offline
Joined: Sep 2013
Posts: 10,679
Indiana
The pumps speed depends on the throttle. Hydrostatic transmissions are ran by a disk with hydraulic cylinders running 360 degrees around the disk. (For a rough visual, think of a wind chime with long chimes parallel to the ground. The chimes being the cylinders and the top being the disk.)

As the angle changes, so does the speed. The more severe the angle, the faster the speed. If the disk is perpendicular with the ground (or driveshaft depending on the design), the vehicle isn't moving. That said, I don't think the fluid would ever know what stress is. Then again, the faster and longer it's moving, the hotter it gets.

Last edited by dlundblad; 07/12/17 02:13 PM.

03 Jeep WJ 4.0 202k Castrol Edge 10w40 HM Fram XG16
02 Volvo S60 2.4T 186k M1 0w40 Mahle OX149D
97 Chevy Blazer 4.3 153k Synpower 5w30 Supertech ST3980 (Ecore)

Re: Kubota Hydrostat - what range? [Re: Alex_V] #4457418
07/12/17 03:17 PM
07/12/17 03:17 PM
Joined: Jun 2017
Posts: 147
Waco, Tx.
Syntheticuser Offline
Syntheticuser  Offline
Joined: Jun 2017
Posts: 147
Waco, Tx.
Alex,
In my experience, with a little 3011 tractor, low range and rev'ed high produced the least slippage and ran cooler than high range light throttle, which produced the most slippage and heat. Change the fluid often, they can run super hot when under load like dragging a plow.
Similar to a auto car's torque converter I think. If it's not locked up, the converter produces the least slippage on the rev limiter...ergo the higher you rev it the less it slips and generates heat.i used torque pro and my Focus to verify this about an auto trans.

Re: Kubota Hydrostat - what range? [Re: Alex_V] #4457512
07/12/17 05:09 PM
07/12/17 05:09 PM
Joined: Jun 2002
Posts: 6,438
MI
doitmyself Offline
doitmyself  Offline
Joined: Jun 2002
Posts: 6,438
MI
Originally Posted By: Alex_V
I regularly operate several pieces of Kubota equipment with hydrostatic transmissions. In a system such as this, which puts the fluid under more stress at the same ground speed: wide open pedal in low range, or, say, 1/3 pedal in high range?


That's an interesting question that I don't know the answer for. I think that as long as you have proper engine RPM for the HST system to run and cool correctly, it won't matter too much regarding fluid stress in either scenario (just my opinion). You get more torque in low range and more speed in high range. I was taught to run the engine rpm at a minimum of 1700rpm to ensure proper HST cooling and operation. I generally don't run mine lower than 2000 rpm when doing work. You adjust the engine RPM above 2K, select low vs. high range, and foot pedal to match your work conditions (Low speed high torque plowing vs. high speed low torque road driving.). You don't want to lug the engine AND you do not want cavitation and excess HST heat with too low of engine rpm (with resulting low HST pump circulation).

Hope I'm not preaching to the choir here, and you are just asking your question, already knowing about proper engine/HST operation. Maybe it will help someone else here new to HST operation. It looks like the newer Kubotas have an ECM that adjusts engine speed and HST pump operation somewhat automatically.

Re: Kubota Hydrostat - what range? [Re: Alex_V] #4457561
07/12/17 05:58 PM
07/12/17 05:58 PM
Joined: Jun 2017
Posts: 147
Waco, Tx.
Syntheticuser Offline
Syntheticuser  Offline
Joined: Jun 2017
Posts: 147
Waco, Tx.
I've had hydros get so hot working, when unhooked, they barely move the tractors under their own power. Keep em'cool and change the fluid regularly. Again, high rpm, low gear, light pedal position...if possible.
Experience with:B3011 Kabota compact tractor
46hp John Deere compact tractor
1970s International 866 Hydro 6 cylinder.- this tractor was crazy fast...
The bigger ones I use are not hydros.

Re: Kubota Hydrostat - what range? [Re: Alex_V] #4458104
07/13/17 09:35 AM
07/13/17 09:35 AM
Joined: Apr 2016
Posts: 1,198
Campbellsville, KY
Alex_V Offline OP
Alex_V  Offline OP
Joined: Apr 2016
Posts: 1,198
Campbellsville, KY
Ditto on the higher flow concept. I'd have guessed that, too, but I suppose the operating principles of the hydraulic pump that generates the pressure in this case made me doubt what I know about fluid temps in auto applications - that maybe the higher flow>better cooling through the hyd. motor would be mitigated by higher flow and friction through the pump to satisfy flow needs. No worries about lugging here, either - when the engine gets loud and bogs it's time for more throttle.

The main machine in question is a 3-4 year old L4400 that's used for mowing duty 90% of the time with a 3 pt. Woods 7 ft., rear discharge finish mower. So it runs 2,300-2,600 RPM the whole time, but the best ground speed can either be obtained at full pedal in low range, or about half pedal in mid range. Sounds like full pedal in low range might be better. There's also an older diesel/hydro UTV (1,700 hours) that sees some use spraying weeds at a very slow, but consistent pace, and at times it's a draw whether to run about 1/2 throttle in low or barely off idle in M. The 3 cyl. engine right behind me makes me prefer idle in M, but oh well. :P

Sounds like I should do the trans. fluids in all of them at some point. They all get the filter changed every 50-100 hours, but AFAIK the fluid has just been topped off until now.


To quote a friend, "Synthetics, man."

'85 GMC C3500, 454, 132K
'82 Mercedes 300CD, OM617 turbo, 173K (totaled 2018, in rehab)
'85 Mercedes 300TD, OM617 turbo, 217K (wife's)
'67 Suburban, 350, 331K
Re: Kubota Hydrostat - what range? [Re: Alex_V] #4464153
07/19/17 03:11 PM
07/19/17 03:11 PM
Joined: Oct 2014
Posts: 12,558
Idaho
CT8 Offline
CT8  Offline
Joined: Oct 2014
Posts: 12,558
Idaho
How does the 7 ft mower work? I may be buying a new mower and a 7 foot with 1 gear box vs an 8 foot with 2 gear boxes and blades are on my mind.


2015 Ford F150 2.7
2018 Ford F350 6.2
Re: Kubota Hydrostat - what range? [Re: Alex_V] #4465866
07/21/17 07:18 AM
07/21/17 07:18 AM
Joined: Nov 2003
Posts: 1,208
Middle of Iowa
DriveHard Offline
DriveHard  Offline
Joined: Nov 2003
Posts: 1,208
Middle of Iowa
Lots of mis-information on here...

If it is a true hydrostatic transmission with axial piston pumps and motors, they operate most efficiently at higher displacements. We are constantly proving over and over again that low engine speeds with the pumps at higher displacements operate more efficiently. If they are operating more efficiently they are changing less of the engine power into heat, and you are getting more power to the ground.

This does not mean that the tractor has the capability to cool the hydraulic fluid at that low speed though. If the fan speed is dictated by engine speed, then everything might be running hotter simply due to reduced air flow through the coolers. I also don't know if your loop flushing is engine speed related either...so you might be getting less cooling fluid into your loop at lower engine speeds.

If you have the service manual and can shoot me some pictures of the hydraulic schematic I can give you some more details on how your system works.


Smile, it increases your face value
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2018 Alfa Romeo Stelvio TI Sport (wife's)
2011 Silverado Crew Cab LT 6.2L/6spd (tow pig)
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