[Shop-talk] Hydraulic fluid question

[David Scheidt]

On Fri, Jul 18, 2008 at 5:31 PM, Marc <smarc at smarc.net> wrote:
> Thanks for that info. Does that viscosity number factor like regular oil? In
> other words, higher number, thinner oil?  My concern is more for the
> operation of the lift  considering the range of temperatures seen in the
> garage from about 40F to 90F.
>

ISO viscosity is an actual, directly meaningful number (viscosity in
centistokes, (which despite my earlier quip, is a real unit of
viscosity, well understood by tribologists), at a specified
temperature.).  Higher numbers are higher viscosity.  SAE viscosity is
an index into a specification, not a direct reading of viscosity.
Consider the case of lettered drill bits.  You know a C drill is
bigger than a B one, but you don't know it's actual size, without a
chart.  SAE viscosities are the same sort of thing.  There, are, it
happens two different sets in use, which overlap in viscosity, but not
in numbers.  Numbers less than 60 are motor oil, numbers above 60 are
gear oil.  90 wt gear oil is about the same viscosity as 50 wt motor
oil, and they're both ISO 18 oils.

-- 
David Scheidt
dmscheidt at gmail.com