In Reply to: Re: The Hydraulic Oil Story posted by TheOldHokie on December 30, 2013 at 07:03:35:
Disagree...36 coupe was first arguing that SAE 90 gear oil is minimum grade required to protect the hypoid ring and pinion gears in the rear differential based on viscosity with NO reference to GL ratings or EP additives and UTF 134D was insufficient because it was too thin.
Then, you indicated the viscosities of the two fluids were basically equal at 100C.
Agree with the statement and the numbers prove it.
Then, the discussion changed from rear end differential protection to hydraulic system performance, based again on viscosity. How can the two fluids be equal, if one lifts the load and the other fluid fails to lift the load durring summer.
Agree that motors are more sensitive to oil grade than gears and the choice of SAE gear oil grades is rather limited to about four non synthetic grades, maybe five, then double it for synthetic formulation.
When is the last time any member mentioned ring gear failure or that matter transmission gear box failure. However, one of the main topics is always hydraulics.
Next time you visit your local NH or JD dealer look at the 5 gallon pales of UTF stacked to the ceiling vs the 2 gallon bottle of SAE 80W90 on the shelf with dust on it.
Still agree with 36 coupe that the SAE 90 gear oil will develop more pressure than the the UTF because the viscosity of SAE 90 is 4X the UTF viscosity at 100F actual working temperature , NOT 100C, which is only used to classifiy the SAE grade.
However, if the hydraulic system functions properly, believe the UTF will develop "on spec" pressure with resulting lifting capacity.
Notice the UTF does NOT even have a package label viscosity rating.
Had a hypoid gear expert explain that gear oil is required in the rear ends to cushion the dynamic impact forces impossed on the teeth from the backlash.
Film protection is not the only consideration.
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