Motorists know when they’re supposed to change their motor oil. They
have oil life monitors, oil change centers and commercials all telling
them when it’s time for an oil change. Differential oil changes, on the
other hand, often get overlooked. Many people don’t even think of the
differential when performing routine maintenance on their vehicles and
don’t realize four-wheel drive trucks have two differentials and a
transfer case that all require service. In fact, according to one quick
lube company, only one to two percent of their customers purchase a
differential gear lube change.
Most differential wear occurs during the break-in period. Because
differentials are not equipped with filters, break-in metals are
suspended in the oil, causing increased wear as the particles mesh
between the gears. Hauling heavy loads and towing heavy trailers cause
additional stress to the differential during the break-in period and can
cause premature differential damage or failure. Changing the gear lube
after the break-in period (about 3,000 miles) is a low-cost maintenance
investment that provides a significant payoff, including greatly reduced
wear, extended differential gear and bearing life and protection for
expensive vehicle investments. Auto manufacturers recognize the
importance of draining abrasive break-in materials. As seen in Chart 1,
some manufacturers recommend an initial drain interval of between 500
and 3,000 miles.
Differential internal components consist of six gears (one pinion,
one ring, two side and two spider gears), six bearings (two pinion, two
carrier and two axle) and sometimes include a clutch setup for limited
slip performance. All of these parts require high quality, clean gear
oil in order to perform at an optimal level.
Most pickup trucks, SUVs and vans operate in severe service
conditions, including towing, hauling, steep hill driving, commercial
use, plowing, racing, off road use, rapid acceleration, frequent stop
and go operation and high ambient temperatures. These severe service
operating conditions subject the differential to extreme pressures and
operating temperatures.
New vehicles such as turbo diesel trucks and vehicles with V-10
engines boast more horsepower and torque than their predecessors, but
differential designs have remained virtually unchanged. Differentials
today are subjected to severe duty service and encounter more stress and
heat than was seen only a few years ago. Modern gear oils are faced with
the challenge of providing adequate wear protection during severe
service operating conditions, while also providing maximum fuel
efficiency.
In fact, according to a 2005 SAE paper entitled Breaking the
Viscosity Paradigm: Formulating Approaches for Optimizing Efficiency and
Vehicle Life, “Concurrent with the strong drive toward better fuel
economy, consumers have been demanding increased performance, which has
required axle lubricants with enhanced durability protection and lower
operating temperatures. There has been a 34% increase in engine
horsepower over the last decade, while axle gear sizes have remained
constant, sump capacities have been lowered, and drain intervals
extended. In the light truck segment there has been a 93%
horsepower increase since 1981.”
Further evidence of stress and increased temperatures during the
differential break-in period is documented in a 2005 SAE paper entitled
The Effect of Heavy Loads on Light Duty Vehicle Axle Operating
Temperature. A light duty GM truck towing 14,000 pounds was driven from
Orange County, Calif. to the Nevada state line. The test was conducted
with both a new axle and a broken-in axle. Over level ground towing, oil
temperature was measured at 230 degrees F in the new axle and 203
degrees F in the broken-in axle. Oil temperature over the most grueling
portion of the trip, during which a maximum 6% grade was encountered,
revealed the new axle was operating at 350 degrees F and the broken-in
axle was operating at 300 degrees F. Laboratory dynamometer test results
simulating a truck hauling a trailer provided similar results, with
level ground towing temperatures recorded at 266 degrees F with the new
axle and 194 degrees F with the broken-in axle and towing temperatures
(at a 3.5% grade) recorded at 370 degrees F with the new axle and 295
degrees F with the broken-in axle.
AMSOIL
SEVERE GEAR™ 75W-90 and 75W-140 Synthetic Gear Lubes are formulated for
severe service applications, protecting differential gears for extended
drain intervals of up to 50,000 miles in severe service and 100,000
miles in normal service, or longer where specified by the vehicle
manufacturer. Formulated with shear stable synthetic base stocks and an
extra treatment of additives, SEVERE GEAR™ Gear Lubes provide
unsurpassed wear protection and friction reduction, while their
excellent thermal stability prevents thermal runaway, a phenomenon
caused by a lubricant’s inability to control friction and increased heat
under high stress conditions.
AMSOIL
SEVERE GEAR™ Synthetic Gear Lubes are recommended for turbo diesel
pick-ups, SUVs, vans, delivery/utility vehicles, light, medium and
heavy-duty trucks, buses, heavy equipment, 4x4s, tow trucks, race cars,
tractors and motor homes.
AMSOIL
Synthetic Gear Lubes save motorists money through extended drain
intervals.
A test on four separate vehicles further demonstrated the importance
of changing the factory-fill gear lube within the first few thousand
miles. Oil analysis results revealed most of the wear in vehicle one
occurred within the first 6,869 miles. Despite higher mileages, vehicles
two and three only showed slightly higher iron wear than vehicle one.
Vehicle four was the only vehicle which had the factory-fill oil changed
to AMSOIL
synthetic gear lube, and despite significantly higher mileage than the
first three vehicles, it showed a significantly lower level of wear. The
chart and photos below provide visual evidence of the wear materials
present in the differentials of each vehicle. The photos clearly show
that the heaviest amount of wear occurs early in the break-in period.
