So how do you recognize the
good oil from the bad for your car?
The first step is to understand the
differences between the old and the
new, and that requires just knowing
your ABCs. This is because the
lubricants industry uses a simple
two letter code developed by the
American Petroleum Institute (API)
to help consumers select the
appropriate motor oils for their
cars. This API Service Code is
displayed on the motor oil label in
what is called the "API Donut," as
shown in Figure 1.
The code for passenger cars consists
of two letters beginning with "S."
The "S" is followed by a letter that
advances up the alphabet from "SA"
to "SB, to "SC" etc., starting in
the 1920s (skipping "I' and "K").
The current specification is API
"SN", introduced in October 2010 for
2011 and newer vehicles (although
they can be used in older vehicles
as well). The second letter in the
code is critical to read before
buying. This is because it indicates
the vehicle model year the oil was
formulated to service.
As shown above, API "SA" oil was the
first in the API Service
Classification for gasoline motor
oils. These oils were formulated for
use in vehicles built prior to 1930.
That's right, motor oil made for
cars built nearly 80 years ago! The
API cautions, these oils are
"obsolete" and their "use in more
modern engines may cause
unsatisfactory performance or
equipment harm." But API SA
is not alone; the API issues the
same caution for motor oils
designated SA through SE.
Furthermore, although the API does
not issue the same cautions for SF,
SG, and SH, they make it clear these
motor oils are also "obsolete."
So how do your recognize and avoid
the use of motor oils that can harm
your engine? The answer is, look for
the letters that follow the words
"API Service" in the API Donut.
If it's not an SN, SM, SL, or SJ,
then it's an obsolete oil. And if
there is no API Donut on the motor
oil label, BEWARE -
because there is a chance you could
be buying coffee without the donut.