> It is interesting to note that SAE Grade 30 motor oil and SAE Grade 90 gear
> oil have about the same viscosity.
Guess it depends on your definition of "about", the range for 90 weight gear oil
actually spans 40 and 50 weight motor oil, but does not overlap 30 weight. Even
then, it's only the same viscosity at the same temperature. But since they
normally operate at different temperatures, they very rarely have the same
viscosity when it counts.
> It is incorrect to call oil 30 weight or 50 weight. Weight has nothing to do
> with the SAE grade. The SAE grade is a measure of viscosity.
English is defined as she is spoke. And "weight" has been in common use as a
reference to viscosity for a very long time, as in "the quality or state of
being ponderous" (Webster). IMO "grade" is too apt to be confused with the API
service rating, since "good" vs "bad" is the common definition of "grade". And
just try asking for "high viscosity" syrup at the grocery store, rather than
> The W in 20W-50 means Winter.
No, actually it's an arbitrary letter chosen by the SAE to indicate that the oil
meets a separate viscosity specification at a low temperature (and using a
different test method) rather than the usual (for motor oil) 100C. Thus, a
straight 20 weight oil does not necessarily also meet the 20W specification.
> Wow, never thought I would correct Randall on anything. But this is my pet
Peeve away, John, you're entitled to your opinions. But I am going to continue
to try to use the language that most people understand. And I also refuse to
call a footpound a pound-foot :)
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