Gravely Hydro walk behind

[Bob O]

I picked up an older [Maybe ~ 2010] Gravely Hydro walk behind with low hours [155].
I want to service the hydraulics but the manual says 20W-50 Non-detergent Hydraulic fluid. This seems hard to find at least for me. What can I use in its place?

Thanks

[KE4AVB]

Personally I would change it over to the Tuff Torq 15W50 Synthetic oil (187Q0899000, 3 liter bottle[a little over 3 qts]) but that may just be me or use some Hydro-Gear 72751 (12 Qt case?). Either way you want a non foaming oil. I do know most hydrostatic transaxle uses conventional SAE20w50 motor oil but synthetics is preferred.

Let's see what others think here that may have more experience than me but I think a non detergent 20w50 is going to be hard to find.

[bgsengine]

Agree with KE4.. However, I would not mix different fluids so if you want to just "top off" , you will want the same oil as you put in.. but if you are completely draining and refilling, then I'd go with a synthetic non-detergent - (Read labels carefully, do your research) You do not want any oil that is going to create foam (and hydros will vigorously agitate the oil, more so that most engines will do) Other than that, you do want something with the 50 weight property at a minimum, so 10W50 or 20W50 , doesn't necessarily have to be specifically hydraulic oil , as long as the lubricating properties are correct (anti foaming, non detergent, high shear strength- so a synthetic would probably be better if using motor oil, if you can find one that meets specs) - foam in your hydro fluid will give you all kinds of problems - cavitation, whine, dead spots, and enough foam, you suddenly get metal to metal contact in critical moving parts, which is very very quickly fatal to a hydro.... even a .0005 (Half a thousandth) of an inch scratch in the right spot of a hydro slipper plate would cut your torque in half or worse (lack of pulling power) which is why many modern hydro manufacturers don't want to offer replacement parts - just assemblies..(and those that do, may even jack up the price of parts where a couple kits may cost more than a whole new hydro) since the success or failure of a repair depends on your dedication to cleanliness and sterilizing your work space... even tiny defects can give you problems and when people can't fix em, they just blame it on lousy engineering or something - anything but their own selves...

[Bob O]

I'm changing the fluid and filter and I'll assume there will be some of the original fluid left so maybe another fluid change sooner rather then later.
Thoughts on that?

Thanks,
Bob

[bgsengine]

Nah - if you change fluid and filter, you'll have pretty much replaced the vast majority of oil (98% - 99%) which is plenty enough, I wouldn't worry about any remaining oil, unless it is extremely contaminated fluid (in which case there isn't much point worrying about what oil goes back in, cause your hydro is gonna be just about kaput by then) no need to worry about mixing synthetic and conventional oils - especially at that ratio...