How hot is your HST?

[JackJ]

I'm a new owner of a BX1870, and I'm surprised how hot my transmission gets especially since I'm still taking things easy during break-in.

I bought a cheap (but well reviewed) infrared thermometer yesterday. After letting my machine warm up, I drove it for about an hour, mostly up and down my moderately hilly road in high range, with rpm's varying between 2500 - 3000, and the pedal/speed varying, but not maxed out.

Ambient air temp was 65F. HST external temps reached 167F, hottest on the left side above the rear wheel at about the PTO shaft height. The back of axle/diff housing was at about 161F. Not sure if temperatures would have climbed higher if I'd kept going longer, but it was getting dark.

My fluid levels are all correct and the fan is intact. There is of course some HST whine I'm hearing, and it's louder than I would have expected, but from what I'm reading about it I don't suspect it's abnormally loud. But hard to say since I'm new at this.

Now I've read that 100F over ambient is normal, and that's where I'm at. But I'm guessing that driving at moderate/high speed in 2wd on paved roads puts a lot less strain on the transmission than mowing high grass, box blading, hauling loads, etc. I've got about 12 hours on the machine, and I'm doing light work with it, but still trying to take it easy.

Is anyone else able to share HST case temps, especially on a BX? How high do they get when the machine is really being pushed?

I may have nothing to worry about here, and maybe temps will go down after some more break-in time. I'll probably do the 50 hr filter change early, and change the fluid at that time as some recommend.

Jack

 

[rjcorazza]

My previous L3410 HST would see case temps in the 180's in the summer, so the ambient + 100 seems estimate pretty accurate. I wouldn't be concerned.
I will say that driving these machines on the road is not necessarily light service. Running on the road at speed, particularly with hills places a significant load on a tractor. Not saying that there is anything wrong with running a tractor on the road, just that it's not the same as taking a car out for a leisurely drive.

 

[JackJ]

My previous L3410 HST would see case temps in the 180's in the summer, so the ambient + 100 seems estimate pretty accurate. I wouldn't be concerned.
I will say that driving these machines on the road is not necessarily light service. Running on the road at speed, particularly with hills places a significant load on a tractor. Not saying that there is anything wrong with running a tractor on the road, just that it's not the same as taking a car out for a leisurely drive.

Thanks!--that is reassuring. I've wondered about how much load I'm inducing just driving on hills and of course I'm obsessing on babying my new very expensive toy. I can clearly hear the HST working (whining) when I'm driving up hill, but fall and winter I expect to be towing a (small) trailer full of fresh cut firewood up and down steeper hills on trails while in 4wd. I expect that to be a much bigger strain. But then again, they'll be more of a chance for things to cool down while the trailer is being loaded and unloaded.

The new thermometer is fun to play with, so I'll be monitoring this.

 

[skeets]

Jack my BX gets toasty warm, but I have not had a problem with it so not to worry the oil does get hot

 

[CaveCreekRay]

Jack,

When I test drove my 9mo old used L3800 the HST was so loud, my buddy, who has a small green tractor and went with me to haul this piggy home, was pretty sure the HST was about to "explode." It was way loud to me as well but, it was still under warranty so I took a chance. Glad I did. Kubota HSTs are bullet proof but, they are loud.

My friend was used to his JD which has a wonderfully quiet little 20 hp Yanmar motor and an electrically controlled HST. My L3800 has twice the hp and a correspondingly heavier duty HST. I wear headphones and listen to music or talk radio while I work. I save my hearing and have fun doing work. Win-Win!

Ray

 

[rbargeron]

HST's give their hydraulic oil a workout so it heats up.
The heat is not from mechanical friction - its from viscosity of oil being forced thru small passages. Hot HST fluid is expected and normal.

 

[Grouse Feathers]

There is a lot of information on hydrostatic efficiency on the internet, but I couldn’t find a good estimate for a tractor hst. The best estimate I found showed a high of about 80%. An hst can be optimized for a specific speed and around 2500 to 3000 rpm seems to be an optimal range (perfect for a diesel tractor). However, the hst on our tractors are probably further optimized for ease of operation and for tractor performance so efficiencies are probably less than 80%. The point is 25% of the power coming from the diesel is going to be lost in the hst mostly as heat and noise. That is a lot of heat and noise!

One of the reasons you notice the hot hst is that it is accessible. It is hot to the touch, but no hotter than other hydraulic power and control systems. The temperature of your car or truck transmission is in the same range, but the transmission is not easily accessible for touching. Since these systems run hot because of the large amount of heat generated in the systems cooling is critical and that is why the fan on the BXs is so critical.

This was just a quick study, I am in no way an expert on hydrostatic or any other type of transmissions.

 

[Grandad4]

The temperatures you mentioned are pretty normal for a hydrostat setup, as noted. It's only when temperatures climb above something like 200 deg that there is cause for concern. I'll occasionally check the loader hose connectors on mine. If they're too hot to touch, it's time to slow down.

However, the BX does present a bit of a conundrum. Its engine is designed to operate at full speed. In fact, that same engine is used in portable lighting systems, generators and other industrial applications where it is not ever "babied" and runs wide open from the day it begins its working life. The engines in those applications are known to last many thousands of hours, with the key being good maintenance.

Mated to that engine is a hydrostatic drive unit that needs adequate hydraulic flow to work most efficiently. Running with the engine slowed down (to baby it), starves the hydro of adequate flow and contributes to the heat build-up and the whining noise you've probably noticed. Running the hydro with insufficient pressure and flow for extended periods is not good for its longevity.

So is it better during break-in to baby the engine and overwork the hydro, or do you rev the engine to let the hydro have enough HST juice and pressure? I don't think Kubota makes clear which is best, but I figured the engine is proven to be robust even in those industrial settings, but the hydro would be just as expensive to fix and definitely wants good hydraulic flow. So I got the engine rpm's up during break-in... not all the way and not steady for hours at a time, but enough to keep the HST from singing so much.

By the way, sorry for being so long-winded. Hope at least some of that helps.

 

[Kennyd4110]

Ambient temp + 100* is considered 100% normal for hydraulic systems.

 

[rbargeron]

..........Mated to that engine is a hydrostatic drive unit that needs adequate hydraulic flow to work most efficiently. Running with the engine slowed down (to baby it), starves the hydro of adequate flow and contributes to the heat build-up and the whining noise you've probably noticed. Running the hydro with insufficient pressure and flow for extended periods is not good for its longevity........

My understanding is somewhat different on this. Just as a gear-type transmission's efficiency is about the same in first, second or any other gear, an HST's efficiency curve is pretty flat too. Engine efficiency varies with rpm, but hst efficiency changes very little with speed of rotation. The main reason is the pump/motor circuit in an HST is kept full by the charge pump (the first thing getting power from the engine). Once charged the HST doesn't much care what ratio it maintains. The pump/motor fluid transfer rate changes with ratio but overall efficiency only changes a little.

 

[armylifer]

If you really want to baby it for the first 50 hours it is much better to run at normal engine operating RPM range (75% to 100%) and use the lower gear range. The HST is operating more efficiently as more fluid is being pumped through it. Most of the cooling inside of the HST is accomplished by fluid movement.

 

[Grandad4]

My understanding is somewhat different on this. Just as a gear-type transmission's efficiency is about the same in first, second or any other gear, an HST's efficiency curve is pretty flat too. Engine efficiency varies with rpm, but hst efficiency changes very little with speed of rotation. The main reason is the pump/motor circuit in an HST is kept full by the charge pump (the first thing getting power from the engine). Once charged the HST doesn't much care what ratio it maintains. The pump/motor fluid transfer rate changes with ratio but overall efficiency only changes a little.

Couldn't really disagree... that's probably a more precise description than mine. However BX's are renowned for needing to have the engine revved into the high end of their rpm range to generate sufficient flow and pressure to operate the hydraulic systems (3 point, FEL, HST), with any authority. I guess that's probably more a function of the charge pump characteristics than the hydro drive box, and I appreciate your correcting what I said. Great to hear your comments, by the way.

 

[Bulldog]

My L3000 was so hot during the summer it was miserable. I changed the fluid to Amsoil full synthetic hyd fluid and my trans temps dropped by up to 70 degrees depending on what I was doing. If you do a fluid change I would at least go with SUDT2 fluid.

 

[JackJ]

If you do a fluid change I would at least go with SUDT2 fluid.

I was hoping that's what's in there already. This is a brand spanking new BX1870--delivered to my dealer one week before I went to buy it 10 days ago, and it clearly hadn't been sitting on anyone else's lot for any length of time. Can anyone confirm what transmission fluid comes OEM on new BX's these days?

I run full synthetics in our other vehicles and don't mind paying extra for it. Haven't researched HST oils yet, and was planning on SUDT2 when I do the first filter change. I believe I've read that it's a synthetic blend, right? What full synths are there in addition to Amsoil?

 

[armylifer]

Almost all lubricating fluids today contain synthetic polymers and chemical compounds formulated for specific properties that engineers require for any type of equipment you may want to mention. That includes our tractors. There are certain friction properties that are required for them to work correctly. That is why specific fluids are recommended by the engineers. If you start using fluids with properties that significantly differ from the recommended fluids, you can cause premature wear. The Kubota website specifically recommends Kubota branded fluids for a reason. I believe that is because those fluids are the best engineered products for our tractors.

Here is a link to the Kubota website. Check out what is recommended and make your decision carefully. Do you really want to try using fluids that are not specifically recommended? http://www.kubota.com/part/lubricants.aspx

I fully expect to be vigorously flamed for those statements but remember this; if your tractor fails to perform while under warranty and you use fluids with properties other than those specifically recommended by Kubota, you may be paying out of pocket if you have a problem and they can prove that you used fluids that do not meet their specification.

 

[Bulldog]

I was hoping that's what's in there already.

I would say that depends on the dealers mind set. Some don't seem to want to carry the more expensive SUDT or SUDT2 fluid and will and have told their customers that UDT will work just fine. It probably will but the other 2 are a better grade fluid. You will always have some that will never believe or agree that synthetic performs and protects better no matter what.

I would guess it should at least have SUDT but if it was assembled out of a crate at the dealer you never know. May pay you to ask your dealer what they use. I know when I bought my L3000 it came to me with a small leak. When the service guy came to fix it he brought a gallon of UDT and said it was just as good as SUDT. My thought on that if it was just as good they would only offer one fluid.

I'll say this. I was assured my tractor came with SUDT and the Amsoil fluid I changed it to was a night and day difference. Smoother performance cold and cooler operating temps during the summer. In my opinion it's hands down a better fluid than what Kubota offers.

 

[JackJ]

I just crossed the 50 hour mark on my BX1870, meaning my break in period is officially over, though I've been upping the work gradually for some time now.

Today, with ambient temps around 85F, I mowed a neighbor's overgrown lawn with some steep hills, which took close to two hours. I was in low range, but maneuvering around lots of obstacles. At times the workload was really high, going up steep hills while mowing in 4wd. But the load wasn't constant as I had to spend a lot of time maneuvering between sections, and some of it was flat and mostly 2wd. At the end, I drove the half mile back to my house in high range (but 2wd of course, and pto off).

I then immediately checked my HST temperature using an infrared thermometer and measuring at what's been consistently the hottest place I've found, circled in red in the attached pic (is this the pump output point?):


My thermometer read 213F (100C). Now I've read in response to my original post in this thread, and elsewhere, that normal is 100F over ambient, and this is obviously way above that. Also that anything over 200F is potentially damaging to seals, as well as the fluid itself. But I've also read elsewhere that some HSTs on industrial equipment are designed to go much hotter.

Can anyone with a BX and an infrared tell me how hot they get at that point, on a day of hard use?

I did my first transmission oil and filter change about 25 hours ago, using SUDT2 and a Kubota filter. My propeller fan is intact and there's nothing blocking airflow. I did one other time see a high temp of 209F, and that was on a similarly hot day, after a two mile trip in high range on a road with some hills.

I have maybe noticed a slight decline in power when my transmission gets this hot, but it might be something I'm imagining, too. There are no obvious signs of an issue, and I'm wondering if this might be normal, which is why I'm especially interested in actual measurements.

Thanks,
Jack

 

[tcrote5516]

My understanding is somewhat different on this. Just as a gear-type transmission's efficiency is about the same in first, second or any other gear, an HST's efficiency curve is pretty flat too. Engine efficiency varies with rpm, but hst efficiency changes very little with speed of rotation. The main reason is the pump/motor circuit in an HST is kept full by the charge pump (the first thing getting power from the engine). Once charged the HST doesn't much care what ratio it maintains. The pump/motor fluid transfer rate changes with ratio but overall efficiency only changes a little.

I agree. Efficiency is minimally changed by flow rates. Expelling heat is very much changed by flow rates and heat is the #1 cause of HST damage.

 

[maclean]

I drove my garbage cans down to the road...not much of a workout...I'll check again in a couple of days when I move dirt for a couple of hours...but up and down the driveway got your circled in red point up to 118 degrees.

-Mac

 

[armylifer]

I think that you are worrying over nothing. I'll be the first to admit that I could be wrong but if you are not experiencing any problems then temperatures do not mean anything in this context. If I were you, I would document the temperatures that you are experiencing and keep a record or log. If you experience any problems then you have documentation to back up any claim that you may have. Also, ask the dealer that you bought the tractor from if any of your observations are abnormal. Do it in email or other written form and then you will have a record of their responses.

I would bet that over 90% of those on this forum that own BX model series do not have the foggiest notion of what temperatures they are running at. These machines are nearly bullet proof. It will take a really big problem to kill these tractors. I honestly do not think that you have anything to worry about. Again, that is only my opinion, nothing that I have written should be taken as bible truth except maybe that these machines are really durable and nearly bullet proof.