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Motorists know when they’re supposed to change their motor oil. They
have owner’s manuals, 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.
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.”
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. Changing the gear lube after the
break-in period (about 5,000 miles) greatly reduces wear and extends
differential gear and bearing life. Auto manufacturers are beginning to
recognize the importance of draining abrasive break-in materials. As
seen in the chart, some manufacturers recommend an initial drain
interval of between 500 and 3,000 miles.
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 110 degrees F in the new axle and 95 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. |
