ILMA Compoundings December 2017 - 22

The profile of engine oils that are used today has completely changed over the past 30-plus years. The continued drive toward better fuel economy, reduced emissions
through chemical restrictions and lower oil volatility, and
increased equipment reliability has resulted in the use of
"thinner" engine oils. This is reflected by Table 1, which
estimates the average base oil quality that would result from
the SAE grade profiles shown above.
Table 1: Average Blended Base Oil Quality Changes for PCMO
Industry (1985 to 2016)
Property
Corresponding API Category

1985

2016

% Change

Group I

Group II - III (1)

Kinematic Viscosity @ 40°C, cSt

37.5

25.0

33.3

Kinematic Viscosity @ 100°C, cSt

5.9

4.8

18.6

SUS Viscosity @ 100°F

195

130

33.3

Viscosity Index

113

16.5

CCS @ -25°C, cP

5850

1750

70.0

Noack Volatility, wt%

15 - 20

14.3

Saturates, wt%

70 - 80

>95

26.7

Sulfur, ppm

~5,000

<25

99.5

(1) Average quality would represent a hypothetical Group II+.

In the mid 1980s, the primary base oils that were used to
formulate engine oils were from the group that would come
to be called Group I. They had significant levels of sulfur,
and volatility (measured by NOACK) had yet to be formally
aligned with in-service oil consumption and engine emissions.
Since that time, the importance of viscosity index (VI),
volatility, low-temperature fluidity and base oil composition
has become very apparent to the automotive industry. To
achieve better fuel economy, the use of thinner or lowerviscosity oils is required. This has led to a significant reduction
in the kinematic viscosity of the average blended base oil that
is required today, by nearly 20 percent at 100 degrees Celsius
and 33 percent at 40 degrees Celsius.
Lower viscosity would normally result in an increase in
volatility. However, the industry has actually seen a reduction in the average base oil volatility, approaching 15 percent
by NOACK despite the use of thinner fluids. The reason
is through an increase in the mid-boiling point of the base
oil, as indicated by higher VI, and that raises the number of
molecules that can be subsequently fractionated at the manufacturing stage to the desired volatility. At the same time,
the combination of a lower kinematic viscosity (KV) and
higher VI has resulted in a significant reduction in average
base oil cold cranking simulator (CCS) viscosity, by approximately 70 percent relative to 1980s data. This is critical for
engine starting, i.e., cold cranking, thus avoiding excessive
engine wear under such low-temperature conditions.

DECEMBER 2017

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The final element of change to the average base oil
required to formulate passenger car motor oil (PCMO)
products is chemical composition. VI is associated with
paraffins that are more stable under the elevated temperature
conditions of the internal combustion engine. "Paraffin"
comes from the Greek for "against change." This stability
reduces the creation of varnish, sludge, deposits and oil
thickening when balanced with the correct additive system. At the same time, it has become apparent from OEM
and catalyst considerations that engine oils need to carry
limited amounts of chemical elements such as sulfur and
phosphorus. One of the major sources of sulfur in the past
has been from the base oil itself, and with the change in
base oil processing from old-fashioned solvent extraction
to new-technology hydroprocessing, the impact on base
oil composition has been significant. The concentration of
saturated (versus aromatic) components in the base oil has
increased by approximately 27 percent, whereas sulfur in hydroprocessed base oils is almost eliminated. Sulfur contained
within the anti-wear additive system is still important for
finished engine oil formulations but is now found mainly in
the additive chemistry.
The current average base oil quality that is required to
formulate the profile of engine oils today is similar to that
offered by many suppliers as Group II+. The official designation from API is Group II; however, many have coined the
unofficial Group II+ name to represent a quality that is in
the upper tier of the Group II range. Since over 65 percent
of PCMO demand is SAE 5W-20/30, where Group II+
quality is required (i.e., 4.8 cSt at 100 degrees Celsius, ~115
VI), it is not surprising that the average base oil quality for
the entire PCMO grade profile is similar to that required for
the SAE 5W-20/30 segment.
The challenge now is to find the right combination of base
oils to produce that required for the SAE 5W-20/30 market.
The answer was first provided domestically in the U.S. in the
1990s, when companies including ExxonMobil, Chevron,
HollyFrontier (then Petro-Canada) and Motiva introduced
Group II+ quality into the marketplace. At 110 to 119 VI,
this was lower in VI than Group III (which must have VI
greater than or equal to 120), but provides significant base
oil interchange flexibility. Therefore, many blenders used
this Group II+ quality to formulate their low-viscosity lube
requirements.
However, the use of alternative and higher VI base oils
began to increase in the late 1990s, when some independent
bodies ruled that Group III base oils, with VI properties
in excess of 120, could be classified as "synthetic." This
provided a lower-cost alternative to the original synthetic
polyalphaolefins (i.e., PAO, Group IV), and the industry
rapidly began to adopt these higher-VI Group III base oils.
With a target blended base oil VI of ~115 to formulate SAE
5W-20/30 engine oils, companies began to use Group III in

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ILMA Compoundings December 2017

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