Doi you need to change hydraulic/hydrostatic oil after first several changes ?

davehowell · May 2, 2014

Good folks, I was surprised when several Kubota dealer people said that after a couple of hydraulic/hydrostatic oil changes, it was only necessary to change filters unless their was contamination such as water in the oil. One suggested changing filters regularly, but oil only every other suggested change interval. In my B7800 case, that is every 300 hours. I am as delighted not to spend the money or the effort, but all my instincts tell me to follow the book. Yet I observed that when I change the oil, it appears to be just as when I pour it in. Any wisdom? I could not find much info here. Thanks. Davehowell

Gary Fowler · May 2, 2014

Hydraulic oil doesn't wear out like engine oil because the only contaminate is water or water vapor condensation as long as your pump seals are good. If pump seals go out, the engine oil and hydraulic oil can mix, so as long as the oil levels remain constant in both reservoirs, not much can happen to the hydraulic oil other than pick up some wear particles in the filter. Every time I have changed hydraulic oil in any equipment, it looks brand new.
For me it is going to be just filter changes as long as the oil looks clear. In old iron farm tractors, they didn't even have a filter and most people only added oil to replace that lost from broken lines and I don't recall anyone ever having a pump failure. Many TBNer's claim that todays pumps have a much closer tolerance than back then so contaminates can do more damage, but with a filter, there is little likelihood of anything ever reaching the pumps.

oldnslo · May 2, 2014

Oil does break down over time and requires changes but the unknown is how much time. Heat is probably the biggest concern for tractor hydraulics. If the oil gets over 220 - 230 degrees it starts to breakdown some. Again how much depends on oil type, additives, etc.

Another issue is how often do you connect new implements to your system and are the QD's clean. This is a source of dirt entry in your system.

Do you operate your equipment in a dusty environment. Are the rod wipers on your cylinders still doing their job.

I agree that in most cases after the first 100 hrs 99% of the wear-in has occurred and the filters should catch the particles from the dirty QD's, worn rod wipers, etc.