The basics of oil additives P.16
See also
QUESTIONS
O U R E X P E RT S TAC K L E
ALL YOUR QUERIES
FROM OUR READERS
Since additives in a
lubricant over time
will be depleted, is
there any way to
replenish them?
— George Owino
Over time, additives are depleted after
performing the function for which they
were intended, degraded by hydrolysis,
mechanical shearing, condensation
settling, water washing, particle scrubbing, etc.
The rate of depletion or degradation
depends upon the application and
the environment. In particular, heat,
pressure, shear rate, fuel sulfur, soot,
dirt, water, aeration and the presence
of catalytic metals (copper, iron, etc.)
affect the rate of depletion.
Regarding replenishment, whenever you top-up a system with fresh
lubricant, you are in effect replenishing
additives. Likewise, you can perform a
partial drain and replacement, as done
in high volume systems like Marine
and power plants. This strategy can
work if the base oil is not degraded. If
the base oil has been degraded, adding
new oil is analogous to sending a
I checked and confirmed that Automotive gear oil SAE 90 and
Engine oil SAE 40 have
the same viscosity, can someone
mix the two?
— Miriam Kahiga
Common perceptions in many plants and
workshops is that “oil is oil” and “grease
is grease”. However, mixing lubricants is
generally not a good idea.
When the Society of Automotive
Engineers (SAE) designed its viscosity
grading system for automotive oils, it was
not accidental that an SAE 40 oil and an
SAE 90 oil actually have approximately the
same viscosity properties in spite of it being
ostensibly a viscosity-grading system. One of
the reasons for identifying similar viscosity
6
healthy person into a room full of sick
people with the hope that his or her good
health will be contagious. The additives
in the new oil might be compromised
within the first hours of use, leaving you
right back where you started. For small
volume systems like automotive engines, it
is advised to drain and replace the oil with
new fresh lubricant.
Casual addition of additives into formulated oil can be dangerous and should
be avoided. When in doubt, consult your
lubricant supplier.
oils with different indices is to highlight the
difference in additive package. If people get
used to the fact that a “90” is for gear and a
“40” is for engines, then the chances of crosscontamination would be reduced. And that
was a great design feature – putting an SAE
40 into a gear component would probably
not be very serious, but putting an SAE 90
into an engine requiring an SAE 40 certainly
would be.
What are the problems
I can face due to grease
mixing/contamination?
— Abdifatah Ahmed
Contamination is a particular concern
with greases. Unlike lubricating oils where
contaminants can be readily removed via
filtration, once grease is contaminated, it is
a virtual certainty that these contaminants
Regarding
replenishment,
whenever you top-up
a system with fresh
lubricant, you are in
effect replenishing
additives
will be introduced into equipment if the
grease is used. This can result in premature
equipment failure due to abrasion and
fatigue. Similarly, cross-contamination of
different greases through using transfer
tools or grease guns for two different
products should be avoided. Many different
grease thickeners are considered to be
incompatible and can lead to excessive
softening or thickening once the crosscontaminated grease is put into service. Just
like lubricating oils, greases should be stored
with pertinent information such as date of
manufacture, date of receipt, “used-by” date
and product data, including manufacturer
and brand.
We encourage technical questions
from our readers. Lubezine’s team of
lubricants specialist will be on hand to
answer your queries.
Lubezine Magazine | January-March 2012