> Any petroleum engineers out there??

Volks,
I am not a Petrochem Eng, but converse frequently with same. I and
others covered this subject adequately about a year ago and that thread
should be in the archives. Nevertheless, in a nutshell: Synthetic engine
oil, ester or polyolefin based oils do not break down in the standard
sense of the word. Primarily they do not oxidize or combine with 02
(air) and thereby breaking down thier long chain molecular structure.
Mineral based oils have a natural affinity to break down molecularly
with merely the exposure to air and even light. This is why they are
bottled in light proof containers. Mineral based oils will "emulsify"
with water as well forming acid. Your engine crankcase has water in it
in the form of droplets from the outside humidity number that condense
overnight as the engine cools. Synthetic oils do not mix, or emulsify
with water and therefore acids will not form.
Since syn oils don't break down in combination with oxygen and don't
make acid as they interact with engine moisture, the viscosity improvers
last much longer on the multi-vis oils.
Additionally, syn oil's film strength is superior in all ways to
mineral, that is synthetic oil's ability to keep two pieces of metal
from touching each other under pressure and being exposed to heat.
Bottom line, pay for the synthetic. I have been running Royal Purple
synthetic 10w30 in my 87 GL for nearly a year. It does make the engine a
little louder as it is less viscous. However the film strength protects
the engine much better, and the lower viscosity allows the engine to
develop measurably more power and a slight gain in fuel economy.
Regards
Mark B. Magee
87GL
82 Diesel Westy
Kemah TX