The phosphorus
content of new oil is typically
associated with antiwear (AW)
additive. Antiwear additives are
used to reduce wear by limiting
the friction of moving parts.
They do so by forming a thin-
protective film on metal
surfaces.
The most
common antiwear additive used in
engines is based on zinc ester
chemistry, with zinc
dialkyldithiophosphate (ZDDP)
the most common. Zinc
dialkyldithiophosphate protects
engines from wear by the
decomposition products of its
constituents (phosphorus, zing,
and sulfur) forming a protective
film on metal parts. The
phosphorus content of a new
engine oil is typically related
to ZDDP additive in the oil.
![](phosph5.gif)
It is
important to note that API
defines upper and lower
boundaries on the level of
phosphorus in an API SM
passenger car engine oil. The
reason for this is that whereas
a higher level of phosphorus may
be desirable because it comes
from a higher concentration of
antiwear additive, phosphorus
can also result in shorting the
life a vehicles catalytic
converter. As such, the industry
has worked hard to strike a
balance between engine wear
protection and catalyst life.
An engine oil,
within the precision and
accuracy of the test, will
either pass of fail the
phosphorus levels set forth by
API for a API SM engine oil.
For details on ASTM D5185 test
method click here. |