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Re: Synthetic Motor Oil -Reply -Reply



Synthetic motor oils are normally esters (I think PAG or POE or both) or
polyalpha olefins (PAO). 

The most popular synthetic is pao and is synthesized from ethylene
oxide.  I think EO is derived from natural gas, but could be a petroleum
by-product.  EO is precisely reacted/ processed to yield particular
carbon chains, C6,C9,C10,C12 etc.  These PAO fluids are  blended, if
necessary, to a specific viscosity.  The blend is then formulated with a
viscosity improver (VI) copolymer to meet the in grade performance
(5w-30 etc)  spec.  An antiwear, anti rust/oxidant (RO) package is also
added to prevent excessive breakdown and wear on the moving parts.  
The resulting lube presents a flat viscosity curve that simply means there
is not  much difference in the viscosity of cold oil than in hot oil.  It both
cases it is thin and allows for excellent cold weather starts and good
lubrication at operating temperatures.    It is more oxidation resistance
because there are no impurities as found in petroleum oils.  The antiwear
chemistry is consumed, so long time oil change intervals may result in
clean, worn-out  engines.  In view of this, it would seem that cold
climates would benefit from the synthetics flat viscosity curve and
maybe very hot climates because of the stability.  Even though
synthetics are technically superior products, my preference in temperate
climates is a good brand conventional petroleum product changed
every 3-4000 miles at a reliable oil change facility that has a take
back arrangement with a re-refiner. 

I don't know what brands are made with esters but several years ago
one company was using ester turbine oils ( jet engine lube) as a base
stock for formulating engine oils.  I recall that it was very good and was
very oxidation resistant - more so than PAOs.   Esters are more polar
and demonstrate more anti-wear properties than PAO.

As a side bar, synthetics are beneficial in gear boxes particularly in cold
weather.  80-90 gear oil is thicker than molasses in cold weather and
shifting is difficult.  The corresponding synthetic is much less viscous
and provides for easier shifting and some small mileage improvement. 

>From a life cycle point of view, it would be interesting to compare
synthetics to conventional oils.  I suspect that synthetics may be more
energy intensive in the manufacturing cycle and more energy efficient in
the use cycle.  Extended oil changes may level this out, but the energy
consumed in the refining of the more frequently changed conventional
may tilt the scale in favor of the synthetic ??  And at the end-of-life, who
disposes / recycles the synthetic??   I think it is just mixed in with the
conventional??

For more info on polymers and additives, contact Lubrizol in Cleveland -
they are the worlds largest oil additive company.  I think Chevron still
produces PAO and Union Carbide, PAG.  Hinkel in Cincinnati has both
PAO, esters and their own brand of finished lubes. 
John O. Sparks
USEPA
Design for the Environment
MC 7406
401 M St. , SW
Washington, DC 20460
Telephone 202-260-1682
FAX 202-260-0981
e-mail sparks.john@epamail.epa.gov