In Reply to: Re: Hydraulic Fluid Sources and Type posted by Larry Holbrook on March 12, 2019 at 10:29:38:
I was actually commenting on your idea that UTTO as a class is an inferior gear lubricant than conventional gear oils when in fact a good quality UTTO is actually an API GL-4 gear oil. You don't have to accept less than conventional gear oil performance to get the cold weather benefits of a UTTO.
As cold weather performance goes and your experience not withstanding the Xtreme product literature makes it explicitly clear that the oil you are using is not intended for that sort of service. This is directly taken from the datasheet that you linked:
Xtreme™Tractor Hydraulic Fluid is a straight SAE 20 weight product and is designed for use in warmer climates, where low temperature operation is not an issue.
Use Xtreme® Heavy-Duty Universal Tractor Hydraulic Fluid for all-season or cold weather use.
Here is the datasheet for the heavy duty formulation of Xtreme THF.
Xtreme Premium Heavy Duty THF
As you can see it is available in two viscosity grades both of which are all season formulations. The viscosity properties of the heavier oil matches up nicely with the now discontinued CNH Ambra Multi-G 134 (M2C-134D) and is reasonably close to the properties of John Deere HyGard (J20C). The lighter oil is billed as a substitute for John Deere low-temp HyGard (J20D) but falls well short of matching the properties of the real thing.
At the risk of beating a dead horse - if you truly want API GL-4 gear wear performance AND an all season lubricant you will be well served by opting for a generic heavy duty UTTO over the economy fluids. It is well worth the modest price difference.