safe engine rpm "window" difference gear vs hydro

[madmax12]

Did a search, first. Did not see this exact topic discussed. I apologise if it has been beaten to death before. I can't find it.

Bought an HST in May 2012.

Dealer said rpm operation up to my choice. If doing heavy work, keep rpm near highest operation levels. If doing light work, it would do no harm to operate a little above idle...and low rpm is to my advantage, as it would consume less fuel. Less fuel and noise level would be the only reason I would like to operate at lower rpm.

Obviously, if mowing, PTO operation dictates engine rpm, as I have only one PTO speed option - 540...rear finish mower.

But if I'm moving a light pallet, or slowly driving with an empty bucket (pick your own version of some light duty task), is there any problem operating near engine idle or slightly above?

Why I ask...

Yesterday, another (more experienced) dealer said a gear version could operate at low rpm, saving fuel. But an HST should always run at PTO speed. Low rpm on HST would be bad for pump, flow, etc.

I don't really know anything about all of this. Can someone with a real understanding explain?

Thanks

 

[heviduty]

I wouldn't worry about puttering around doing light work at just above an idle unless it's really cold or you do it for a long time. From what I understand, the only reason to keep the rpm's up when not using the pto, or not working it hard, is to keep the engine temp up (which prevents carbon buildup), which could be a concern in your area in the winter. Our local dealer recommends not running less than 1500 for long periods.

 

[madmax12]

I wouldn't worry about puttering around doing light work at just above an idle unless it's really cold or you do it for a long time. From what I understand, the only reason to keep the rpm's up when not using the pto, or not working it hard, is to keep the engine temp up (which prevents carbon buildup), which could be a concern in your area in the winter. Our local dealer recommends not running less than 1500 for long periods.

Your advice matches the operator's manual. It has the same warning for cold weather. However there is no info to indicate any difference/danger with gear vs hydro rpm operation. Thank you for your reply.

 

[heviduty]

Your advice matches the operator's manual. It has the same warning for cold weather. However there is no info to indicate any difference/danger with gear vs hydro rpm operation. Thank you for your reply.

I would interpret that as "no difference".

 

[94BULLITT]

My 4240 has a auto throttle advance so I almost always use it. My bx and the bobcat I had seem to operate good at 2000-2200 rpm. The hydro is not as responsive at idle or a low rpm. Sometimes on the bx I put the hydro pedal to the floor and control my speed with the throttle. I don't think carbon is as big of a deal with ULSD fuel,

 

[Gary Fowler]

When roading my B26, I run it pedal to the floor and what ever RPM needed for speed. I see no need in reving the engine to 3000 RPM to go 5 MPH when 1200-1800 is plenty. My B26 idles higher (1200) than my LS (900) which maybe is due to the hydrostatic in the B26. I rarely run the Kubota at max rpm for anything as it just seems like it is running too fast and much too noisy. 2400 RPM or less works for back hoe work which is about all I do with it. FEL work, the rpm comes down to about 1800 and it has power to spin all the tires in 4WD without stalling the engine.

 

[madmax12]

I would interpret that as "no difference".

Unless someone teaches us differently, I'm inclined to agree with you.

 

[madmax12]

94BULLITT and Gary, thank you for your replies.

 

[crazyal]

I usually don't go too much lower than 1800. The fuel difference isn't much and I figure at 1800 there's lots of oil moving around plus there's plenty of power to move.

 

[TripleR]

I would have to just pretty much repeat what the others said, I run HST as well as gear and unless running something off the PTO as mentioned, run at the speed that gets it done comfortably though on none of my tractors is this "just above idle", usually no lower than about 1200-1500, but this may vary with different tractors/models.

 

[madmax12]

thanks crazyal and TripleR

 

[k0ua]

I sometimes run the rpm down around 1500 when I want hydraulics to be a little less responsive, like when smoothing gravel by traveling slowly, or setting a rock with the forks. I don't lug down the engine, but get the job done a little smoother. I don't think it hurts anything, I have been doing it for a while.. Also I mow sometimes at less than 540 speed also because it doesn't sling rocks as far. This is with a rotary cutter. Of course the cut is not quite as good, but a heck of a lot less violent when you are going over some possible rock area.

James K0UA

 

[murphy1244]

I never go below 1500 rpm, got to keep that oil preasure up. You will know when you are going too slow when the motor lugs as you are stepping on the go pedal.

 

[madmax12]

k0ua and murphy1244, good points. thanks

 

[Franko]

Guys,
Good questions and answers. My question is close to this one. I noticed that my Kubota B7800 goes a LOT faster in Hi gear when moving up and down my 900 foot driveway, and unloaded I have no problem. I was hauling load after load of dirt in the loader back and forth recently and decided I just needed to get out of M and into H to get er moving and get the job done. However, there are a couple of steeper areas and the engine bogged down and made a lot of noise at the 2000 rpm I was using so I upped it to 2300 or so and feathered the pedal a little to keep the RPM up and get up the hill. It all seemed to work, and I got the job done a LOT quicker than I could have in M gear, but I wondered if I was causing undue strain with that kind of operation? The engine was running nice and cool - I guess I am more concerned with the HST. Can it take it?

Frank

 

[CompactTractorFan]

I find it really hard to follow advice about RPM's from those who don't have the same tractor as me. You have to take into account that different engines are rated at different RPM's.

For example, my BX25 is rated at 3200 RPM while TripleR's L5740 is rated at 2700 RPM, so it really depends on the tractor. There is no one "magic RPM" that applies to all tractors.

That's my :2cents:

 

[k0ua]

I find it really hard to follow advice about RPM's from those who don't have the same tractor as me. You have to take into account that different engines are rated at different RPM's.

For example, my BX25 is rated at 3200 RPM while TripleR's L5740 is rated at 2700 RPM, so it really depends on the tractor. There is no one "magic RPM" that applies to all tractors.

That's my :2cents:

Well of course you are right, but I think the bigger point is not the specific RPM you should or could operate at, it is that if your tractor is not lugging down, and you are putting a light load on it, you could safely operate it at something less than the rated 540 setting.. I think that is what we are trying to get across.

James K0UA

 

[heviduty]

Guys,
Good questions and answers. My question is close to this one. I noticed that my Kubota B7800 goes a LOT faster in Hi gear when moving up and down my 900 foot driveway, and unloaded I have no problem. I was hauling load after load of dirt in the loader back and forth recently and decided I just needed to get out of M and into H to get er moving and get the job done. However, there are a couple of steeper areas and the engine bogged down and made a lot of noise at the 2000 rpm I was using so I upped it to 2300 or so and feathered the pedal a little to keep the RPM up and get up the hill. It all seemed to work, and I got the job done a LOT quicker than I could have in M gear, but I wondered if I was causing undue strain with that kind of operation? The engine was running nice and cool - I guess I am more concerned with the HST. Can it take it?

Frank

Franko, I have noticed my pedal back force will increase when overworking the HST. I do not know if it is by design, but it happens. When that happens (I am usually in high range going uphill pedal down with a load), I, like you, know to back off the pedal and increase rpm. Maybe the wrong thing, but it works for me, and no problems ... so far.

 

[TripleR]

Guys,
Good questions and answers. My question is close to this one. I noticed that my Kubota B7800 goes a LOT faster in Hi gear when moving up and down my 900 foot driveway, and unloaded I have no problem. I was hauling load after load of dirt in the loader back and forth recently and decided I just needed to get out of M and into H to get er moving and get the job done. However, there are a couple of steeper areas and the engine bogged down and made a lot of noise at the 2000 rpm I was using so I upped it to 2300 or so and feathered the pedal a little to keep the RPM up and get up the hill. It all seemed to work, and I got the job done a LOT quicker than I could have in M gear, but I wondered if I was causing undue strain with that kind of operation? The engine was running nice and cool - I guess I am more concerned with the HST. Can it take it?

Frank

Pretty much agree with how you and Heviduty are operating, as long as you adjust your RPM and pedal position to where you aren't lugging your engine, you should be fine.

I find it really hard to follow advice about RPM's from those who don't have the same tractor as me. You have to take into account that different engines are rated at different RPM's.

For example, my BX25 is rated at 3200 RPM while TripleR's L5740 is rated at 2700 RPM, so it really depends on the tractor. There is no one "magic RPM" that applies to all tractors.

That's my :2cents:

I thought that is what I said in my response as we use a BX2660, L5740 and M8540, so you operate at the RPM's that work well for you HST or geared.

Well of course you are right, but I think the bigger point is not the specific RPM you should or could operate at, it is that if your tractor is not lugging down, and you are putting a light load on it, you could safely operate it at something less than the rated 540 setting.. I think that is what we are trying to get across.

James K0UA

Yep, pretty much; we are just giving general guidelines as each model will vary. As mentioned on diesels I like to keep the RPM's turning enough to burn good, keep the temperatute and fluid flow going good. Over time, you will find yourself able to run pretty close to ideal by feel.

 

[heviduty]

I remember reading years ago, "Lugging an engine can't hurt it, over revving can." Is this no longer a valid statement? Can you harm a diesel engine by lugging it?