ARD-WORKING DIESEL ENGINES present a serious challenge
to the lubricants that protect them. Tight clearances
and intense pressures can generate enough force to tear
apart the molecular structure of the oil, causing permanent
viscosity loss. Permanent viscosity loss is termed
"shear" and leads to accelerated equipment wear, oil
consumption and deposit formation.
Shear stability measures a lubricant’s ability to withstand
shearing forces without degrading to a lower viscosity.
To meet CJ-4 requirements for shear stability, the
American Petroleum Institute (API) requires diesel oils to
pass the Kurt Orbahn 90-Cycle Shear Stability Test.
Resisting shear and maintaining protective viscosity in
the harsh operating conditions of diesel engines is challenge
enough for many diesel oils, but maintaining viscosity
in the face of fuel dilution is another challenge
altogether. Factors such as frequent starts, excessive
engine idling, short trips and cold weather have contributed
to moderate levels of fuel dilution in diesel applications
for years, while recent issues with emission systems
have brought the fuel dilution problem to a whole new
For example, AMSOIL has documented increasing fuel
dilution levels in 2007-2009 Caterpillar C13 and C15 onhighway
engines. There are many possible causes, including
problems with a unit injector or leaking seals. Another
cause of fuel dilution is new emission systems using incylinder
post-fuel injection, a process most 2007-2010
light-duty GM, Ford and Dodge diesel pickups use to
regenerate the diesel particulate filter.
Because diesel fuel is a natural solvent, it causes a
multitude of problems when it contaminates the
oil, including reduced oil viscosity, reduced oil
fi lm strength, increased engine wear (particularly
in the cylinder/ring area), increased volatility,
weakened lubricant detergency, accelerated
lubricant oxidation, varnish formation, acid formation/
corrosion and low oil pressure.
The most notable problem associated with
increased fuel contamination is reduced viscosity
and the corresponding effect it has on oil
performance. When combined with shearing
conditions, as little as 4 percent fuel dilution is
generally enough to reduce an oil’s viscosity to
less than the specified viscosity grade.
AMSOIL sent five competitive synthetic CJ-4
5W-40 diesel oils to an independent laboratory
for shear stability testing. Knowing the tough
environment that diesels present to lubricating
oils, AMSOIL doubled the standard Kurt Orbahn
90-cycle test and had the oils tested for 180
cycles. Samples were then contaminated with 2
and 4 percent ultra low sulfur diesel (ULSD) fuel.
As the graph shows, even after being shear
tested for twice the industry standard and
concontaminated with 4 percent fuel dilution, AMSOIL maintained
viscosity and was the only oil to stay within an SAE
40 viscosity rating. As other oils lost viscosity due to
shearing forces and fuel dilution, their ability to protect
against wear was jeopardized.
"The superior shear stability of AMSOIL Premium API
CJ-4 Synthetic Diesel Oils, even in the face of fuel dilution,
is a significant selling point,"
said Executive Vice President Alan Amatuzio. "Although
some emission system hardware has forced AMSOIL to
scale back its drain recommendations in the corresponding
applications, shear stability test results show AMSOIL
is the best choice for keeping diesel engines protected
and running at peak performance."
AMSOIL Premium Diesel Oils are formulated with an
ultra shear stable polymer system that maintains viscosity
better than inferior products. Testing proves that
AMSOIL provides unsurpassed shear stability, offering
better viscosity control than competitive oils.
Even though recent fuel dilution issues forced AMSOIL
to adjust its Premium API CJ-4 Synthetic Diesel Oil drain
interval recommendations in 2007-2010 Dodge 6.7L, Ford
6.4L and GM 6.6L light-duty turbo-diesel pickups and
2007-2009 on-highway Caterpillar C13 and C15 engines
to the manufacturer-recommended drain intervals,
AMSOIL Premium Diesel Oils remain the premium choice
for diesel applications. AMSOIL Premium Diesel Oils
resist viscosity loss from both shearing forces and fuel
dilution to maintain their protective fi lm strengths, providing
superior protection to all diesel engines.