aviation oil vs. automotive oil

[Ralph Baker]

I was hoping a more knowlegeable person than I would respond. Having
road raced two stroke motorcycles and riding street bikes for years some
oil information has come my way. The Lycoming and Rotax engines operate
in different environments. The Lycoming clearances are large and
temperatures flucuate widely compared to water cooled engines with much
tighter clearances. They also are designed for highly leaded fuel
(compared to the old auto fuels) as well as having greater corrosion
issues. Oils are all basically the same with respect to base stock and
the major difference is the additive package.

The guys with lineups of dynos at their disposal can test the additive
package versus corrosion and wear and adjust for best application. As
an example, phosphorus and calcium compounds are used as "last ditch"
lubrication components in auto oils up to "SG" designation. After that
they were vastly reduced because of the catalytic converter effects.
The later oils are not necessarily better and Rotax four strokes are
better served with SG rated oils such as Golden Spectro motorcycle oil.
Another example is the TCW-3 two stroke outboard oil differing from the
aircooled two stroke oil for chainsaws.

I like building and (eventually) flying an experimental aircraft but
will not let the experimentation extend to engine oil. The delta oil
cost is not a good tradeoff against a Lycoming rebuild before TBO.
Ralph Baker




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