HST Drain Oil Observation

During this shutdown I attended to deferred maintenance on the RTV900 and BX tractor. The HST fluid was drained from both machines and replaced with Super UDT2 and OEM filters.

The RTV HST oil was a clear amber color with just a few particles on the drain plug. I don't know the hours on the oil. During test runs I noticed the engine bog on hills is gone.
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The oil from the tractor was dark and had a burnt odor. It was over the recommended 200 hr. limit by about 300hrs. (shame on me). Unlike the RTV this has one filter and a strainer screen on the suction side. The screen had just a few metal particles.

Not sure what the burnt smell was about. The HST fan had few blades missing but fixed that last year.

Any thoughts about possible harm done, seems to run as it should. Should the HST fluid be changed prior to next recommended 200 hr. change interval?

The tractor is mostly for mowing a 1 acre hilly lot and pulling a tree chipper through the woods.

i wouldn't worry to much. i don't know about the dark oil on the tractor unless it was getting contaminated from sharing hydraulic cylinders from other machines. chances are the old oil was just plain old UDT and that explains the performance jump on the rtv.

I agree . I'd just keep an eye on the tractor's fluid color and see how it goes. The SUDT2 is synthetic and will make a difference in performance- at least it did with my machine . It's good stuff.
On my Kioti tractor 2011 model DK40se , The fluid is so clear that I have to put the edge of the dipstick on my finger and hold to the light in order to see it. I only use it to spray pasture ( currently doing that this month and for gardening) only 459 hours. I took off the bucket because of the bouncing when spraying ,but that , the pto roller pump and the pto tiller is the only things I've ever put on the tractor.

We had the same thing happen to a bobcat skid steer. Engine oil way over recommended change. And the only reason it was changed is the oil filter came apart. The oil was dark and had a burnt odor but no residue. After a new filter and oil change, it was run about 25 hours on a job. I checked the oil it was no longer the color of honey, it was darker. I do not think it should have become that dark that soon. I suspected there were carbon deposits or sludge that came from running it too long before change. So at about 30 hours, I changed the oil and filter again and it was clearer. I stepped up the change interval and over time it cleared up. I don't know what causes that darkness for sure but that is what worked for me.

i have noticed through the years that most folks focus on hours when they decide about service intervals. one thing that is a huge killer in these or any HST is water. some oils are better than others at tolerating water without compromising lubricity and corrosive properties. not all oils are created equal so if you are using a certain brand you should be familiar with their recommendations. another big problem i think especially in the rtv family is that some of these get started and shut off frequently and the oil never gets up to operating temp long enough to help dissipate moisture before they get shut down and repeat over and over. in this way the service hours stay low and the owner feels like they can go years before service. in these cases the oil should be changed at least once per year regardless of hours and maybe sooner in some cases. a machine that is used hard will most likely fair better in extended interval than a rarely used machine. if changing the oil is to expensive then maybe you should get a belt driven machine??? there are to many failures of machines with less than 1000 hours on them.

Had this discussion with my neighbor who purchased a Kubota tractor with HST. It's a higher HP version of my BX which he bought new for $34K. He quoted the specs from the manual...100hrs for the first HST fluid change. After 7 yrs. he was still under 100hrs so it did not yet happen!

I believe its still running with the factory fill crankcase oil. After my rant he arranged for Kubota field service to give his tractor a full service.

The Kubota Tech agreed with the 100hr. spec and said the HST service was unnecessary. I'm reminded of this every time we discuss tractors.

i think Kubota corp could do a better job of describing maintenance guide lines. they could take a lesson from Toyota and Lexus. even Cat and John Deere etc. my favorite is Lexus in the land cruiser format they give very specific format for service interval by miles and time. it is structured to go out many many years. it works.

I'm seriously guilty of letting oil changes wait too long on my equipment. A lot of my equipment is/was used pretty heavily when I got it but once you get all the big chores done and you're in maintenance mode, things just don't rack up hours.

I also probably have too many pieces of equipment for what needs done. Heck, wife and I are retired but still have 6 vehicles. She has a Lexus and in the last 4 years she's driven it... 40 miles total.


For the RTV, I just have a hard time swallowing doing a HST oil change every year when it only got a few hours on it during that time.

bczoom said:

I'm seriously guilty of letting oil changes wait too long on my equipment. A lot of my equipment is/was used pretty heavily when I got it but once you get all the big chores done and you're in maintenance mode, things just don't rack up hours.

I also probably have too many pieces of equipment for what needs done. Heck, wife and I are retired but still have 6 vehicles. She has a Lexus and in the last 4 years she's driven it... 40 miles total.


For the RTV, I just have a hard time swallowing doing a HST oil change every year when it only got a few hours on it during that time.

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getting it up to operating temp is very important and also the SUDT2 is very very good at controlling water. much much better than some cheaper oils.

I use SUDT in the Kubota, Hy-Gard in Deere. The only place I use generic is in the log splitters. They just don't care what you feed them.
I'm thinking about adding some SeaFoam to the oil. I use it on the fuel side but I hear it has purposes on the oil/lubricant side.

don't use seafoam in the transmission oils. it can be added to engine oils but only if you need to clean something bad up. seafoam is good for fuel. some of the best oil out there for constant mesh powershift and hydrostat transmissions id IH ultraction.