In Reply to: Re: The Hydraulic Oil Story posted by raVen on December 30, 2013 at 10:19:07:
There is no argument that a heavier oil will compensate for worn clearances in a hydraulic pump. Can we put that to rest please.
Hydraulic oils are graded using the ISO system where the reference temperature is 40C (100F).
As I said earlier at that temperature (40C) the viscosity of most UTF's is 60-65 cSt making it equivalent to an ISO 68 grade hydraulic oil. That is a commonly used grade and you will find it in abundance at places like TSC.
Usng your 4X metric that would make SAE 90 an ISO 220 grade hydraulic oil. That is a very heavy hydraulic oil and you will likely have to visit a specialty hydraulic supply house to get it. It is not the sort of thing that gets used in ordinary mobil or agricultural tractor hydraulic systems and would probably be deemed unsuitable for use in many such systems
The commonly used grades of hydraulic oil for mobil and agricultural applications are ISO 32, ISO 46, and ISO 68. At 40C all of those grades will all produce 3600+ PSI in a generic OTS gear, vane, or piston hydraulic pump. That is typical of the maximum rated pressure for those types of pumps and more than many hydraulic system components are rated to handle. You do not need anything heavier to get that kind of pressure unless the pump is worn the heck out.
UTF is a universal tractor transmission fluid and is not formally graded as hydraulic or gear oil in the same way ATF is not graded as a gear or hydraulic oil. Neither of those two oils fit into those product categories and consequently are not labeled as such. Both have readily available product data sheets that provide viscosity data if you want it.
The numbers are all there - all it takes is the time and energy to find and understand them.
TOH
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