Sludge may eventually clog critical oil passageways preventing necessary oil
reaching vital engine parts. This causes excessive wear and eventually failure
of various engine parts. Synthetics simply do not react with oxygen.
Petroleum oils readily react with oxygen. To counter this reactivity petroleum
oils are treated with anti-oxidation additives. When oils are operating in the
intermittent temperature range (higher than normal) they are susceptible to
higher rates of oxidation and thus, sludge buildup. Unfortunately, today’s
engines are forcing oils to operate at 230 to 250 ° F routinely. This puts
petroleum oils in a range of temperatures that causes increased use of the
anti-oxidants in the additive package and shortens the life of the oil.
Synthetic oils are in the normal operating band for temperatures in excess of
330 ° F and suffer little or no oxidation at all. This is one of the reasons you
hear of technicians reporting how clean engines that use synthetics are even
with high mileage.
Advantage: Very strong for synthetics
Volatility: How easily does the oil vaporize or boil off? When oils are hot,
vaporization can result in significant oil consumption and thickening of the
oil. Not only is this a problem for oil consumption, but also results in
increased tailpipe emissions. Because of the chemical makeup of synthetic
motor oils, they are much sturdier and more durable than petroleum oil in the
hot engine environment; consequently, they resist vaporization or boil-off
from high operating temperatures much better than petroleum oils.
Advantage: Strong for synthetics
Seals: How are seals affected? Will the oil cause them to shrink or to swell?
And is the oil chemically compatible with them? Seals are made of a variety
of compounds to provide rigid but flexible surfaces that promote good
sealing in order to keep liquids in and dirt out. Petroleum oils are fully
compatible with the seal materials used in modern engines and will slightly
swell the seals. Some synthetic oils tend to shrink seals, therefore causing
minor oil leakage. Historically, seal compatibility issues have caused real and
imaginary problems for synthetic oils in the market place. Currently, seal
issues for properly blended synthetic oils are no longer an issue.
Advantage: Slight for petroleum