PLEASE READ - RE:confused about synthetic gear oil

[Robert Deutsch]

OK, here's the skinny.

The first thing people have to do is forget the myth that synthetic oil
is "thinner" than other oils. The fact that it is synthetic has nothing
to do with that at all. What synthetic means is that the oil is made of
synthesized molecules of oil; i.e.: each oil molecule is a "perfect"
one, that it will perform to the best of its designed purpose, and that
the breakdown will be slower than that of multi-grade oils that contain
some "non-perfect" molecules.

When it comes to how "thick" an oil is, the viscosity is the measure of
the "thickness". The use of two numbers in the viscosity ratings of oils
such as 15w40 shows the range of the oil's viscosity. So a conventional
multi-grade gear oil with a viscosity rating of 75w90 is the same
"thickness" as a 75w90 synthetic gear oil, only the synthetic oil will
break down slower. The higher the viscosity rating numbers (especially
the second one of the two), the "thicker" the oil is. Now, one thing
that people should also keep in mind is that different oil companies may
use different processes and include different detergents and additives
in the oils which may make two oils of the same viscosity seem
different. Also new oil will perform differently from used oil so there
may be a change in apparent "thickness" after a fresh oil change.

(On a bit of a tangent), one of my pet peeves is the fact that some
manufacturers, dealerships, and shops (oil change outlets) do not
explain that the viscosity of the oil must be chosen for the climate and
operating conditions that the vehicle will be used in. For those who do
not know what cold is, here in the province of Saskatchewan, Canada, we
hit temperatures of -40 C (-40 F) and -55 C (-67 F) with windchill this
past week. Now when it is that cold, only 0w30 viscosity oil will give
you any hope of turning over and possibly starting your vehicle.
Anything "thicker" and you have a frozen block of oil in your oil pan
that will never reach the top end of the engine.

When it comes to gear oil, some transmissions (because gear oil is so
thick) will pull the vehicle forward from the viscous friction between
the oil and the gears. Once it warms up, (which should only take a
minute or so depending on the temp) it will no longer do this. My advice
to those in cold climates that have standard trannies is to start the
vehicle with the clutch pedal held down for a while to let the engine
run somewhat smoothly, then slowly let go of the clutch pedal to allow
the gear oil to begin to circulate slowly and not jerk the vehicle
forward.