Hydraulic Fluid - Confused?

[coder]

It is not entirely clear why they specify a 15w50 or 20w50 motor oil for this application.


Some people think it is just a lazy spec, which goes like "oh well motor oils are easy to get so why not"
There are some who think the multigrade SAE viscosity they ask for is optimal for the high heat, high oil pressure app.

We do not have a detailed explanation of their reasons, but we do not have much of a choice, other than following
the manufacturer's recommendation. The only choice I see is selecting a traditional or synthetic oil, fitting the
known parameters they spec-ed.

I have seen motor oil spec-ed in lawn tractor tranny's too, my Scotts tranny asked for the
same thing, 20w50 motor oil, so this is nothing new.

From what I gather, the requirements are some minimal level HTHS, 15w50 or 20w50,
I think there is an implied high anti-wear and anti-oxidant additive content "ask" here,
as the heavy multigrades specified do not limit the anti-wear additives, neither would the ancient SF spec or whatever
they actually asked for.

I prefer synthetics for stability over a long time. For me that translates to some mostly pao or gtl+pao mix oil.
I talked to M1 support, and they confirm that the M1 15w50 red label synthetic is a recommended product
for this application. So that is one safe bet.

There are some oils that seem to be custom engineered for these hydros, e.g.: amsoil . I imagine the specific requirements
could be obtained by lubricant formulators, so that they can design a product that is optimal. Those 2 ( m1 and Amsoil) would be my top
2 choices for this.

I see no point of paying the unreasonably high prices for the OEM branded "hydro fluids" (Stens, Gravely, Scag, Hustler, Hydrogear etc... they all have their own brand) ,
which are either of undislosed composition (often mineral), or just rebranded synth blend/synthetic motor oils.

 

[bertsmobile1]

Oils are liquids so they do not compress very much
As such they can be used for power transmission as well as lubrication.
And as most pumps generate friction and need both lubrication and a means of removing heat so oil is fine in a hydro transmission.
All oils are basically the same but we put extra stuff in there to do things like stop it from frothing , hold crud in suspension or drop crud to the bottom, take more pressure , prevent burning, prevent boiling, prevent freezing , wet surfaces better, not wet surfaces etc etc etc .

Purely synthetic oils are made by converting gases like propane into oil.
They are very expensive because it takes a lot of gas to make a tiny amount of oil and that gas could have been sold as LPG.
All the others are nothing more than oil broken down into all of its component parts then reassembled using only exactly what you need for the product.
In reality they should be called "Super refined" or "Reassembled " oil, synthetic is not the correct description.
However because of the extral processing needed, they are also more expensive but not as expensive as truely synthetic oil .

Now refining is expensive so what generally happens is they take out what is very dangerous to the end use , what is not needed but can be sold for a profit and what is left over is engine oil.
The important thing is it is cheap.

We do the same thing with a mile of products
Soft serve Ice cream is not ice cream it is made from corn starch so we could be calling it "synthetic ice cream " but because we eat it, the idea of eating "synthetic food " is science fiction creepy , so it is not done .
However oil goes into a machine and a machine is man made so oil that is man made ( synthetic ) must be better , obviously.

Now hydros have been around for ages
The 1956 , 100Hp Oliver draught tractor has a hydro drive , just in case the 2 mph bottom gear is too fast for whatever the impliment you are towing is doing.
This hydro runs off the main hydraulic pump then goes through a second hydro pump then the motor then the bull gear and as such uses hydraulic oil
It could have used the engine oil or even the gear oil but the hydraulic oil is already under high pressure so requires less energy to boost the pressure than either of the other two would.

 

[slomo]

I'd use the mower or hydro makers branded fluid. These toys can cost over 10 grand. No doubt the manufacturer has formulated their oil with special additives for that application. Also protects your warranty.

Using car oil off the shelf from Walmart makes 0 sense. As in the cheapest so called synthetic (Mobile 1) you can buy.

slomo