Critical Temp for HST and its Fluid

Tractor Seabee · Aug 16, 2016

I have been searching for info on the maximum operating temp for my BX25 HST. Chewing up my HST fan is a constant possibility with the where and how I operate the tractor. Currently need to have the fan replaced (over $400 labor to replace a $12 part). Good thing I have KTAC insurance. I have no idea how long I ran without the fan. A temp increase would be a simple indicator if K had installed an oil temp gauge. Worked pretty hard yesterday moving a bunch of logging slash and temp got up to 200 F on the HST case and 160 F at a FEL cylinder. Those temps do not seem to be excessive.

The WSM is silent on the subject. Previous such emails to K have been ignored. Dealer shop had no idea.

This being the prime work season I hate to tie the tractor up for a month in the dealer shop getting the fan replaced. Reduced operating time is a better solution till winter. My trusty infra red laser thermometer can keep me safe if I know what temps I need to watch for.

Maybe our friends at Messicks can weigh in on this.

Ron

KyleH · Aug 16, 2016

What is causing your fan to break so often? Can you make a guard for it? A temp sensor or switch could be installed if you feel it would keep your mind at ease.

As for temps, can't say for sure on your specific application, but if you search hydraulic fluid temperatures, companies such as Mobil 1 claim 110 to 150 deg F is normal for most applications, but can handle up to 200 deg F if the right fluid is used. I normally set cooling fan switches to come on around 140-150 Deg F on hydraulic coolers on lube trucks just for an idea.

Normally you will be able to smell the fluid to determine if it has gotten "burnt" but if in doubt it's good to just replace it, also check hoses that are flexible that may had degraded if any material (black dust or flakes) is suspended in the fluid.

number two · Aug 16, 2016

I have always remembered that general practice is 100 degrees above ambient temperature is normal for machine fluids.
Coolant-200F at 100F-seems OK
Motor oil-200 at 100F-why not?
Hydraulic oil-200F at 100F-sounds OK to me!

Good Luck!

Deano · Aug 17, 2016

Make a guard for it. Full bottom plate.

buickanddeere · Aug 17, 2016

How about an ordinary electric cooling fan from a vehicle radiator operated via a thermal switch. 212F is ok for oil temp and seals and dries the water out but much above 220F and oil break down increases exponentially .

MHarryE · Aug 17, 2016

For good hydro life you really want to keep the oil temperature at 90C or below (194F). It's best if the oil viscosity is at least 16 cSt which I believe is around 180F with UDT.

dstig1 · Aug 18, 2016

From my experience with hydraulics at work, roughly 200F is the upper limit for typical hydraulic fluid. Seems in line with what every one else is saying. Now the case temp will not be the same as the fluid temp.... fluid would likely be hotter, so a buffer of 20-40 deg would be wise if you are measuring case temps, depending on how close you want to cut it.

Tractor Seabee · Aug 19, 2016

Thanks a lot guys. The 100 degrees over ambient seems to be the consensus including the shop foreman at my dealers. He said as far as he knows Kubota does not discuss what may be the CRITICAL TEMP (the point where mechanical damage occurs or fluid is destroyed as applicable). I have a long stem thermometer so I will check case temp and fluid temp differences. My shop foreman stated for this climatic area he has never seen HST damage incurred on a broken fan job.

Ron