Viscosity Index

As temperatures rise, gear lubricant viscosity and loadcarrying

abilities decrease. A lubricant’s viscosity index

(VI) indicates its ability to maintain its protective viscosity

in high temperature service. The higher a lubricant’s VI,

the less its viscosity changes in temperature extremes.

The ASTM D-2270 Viscosity Index test measures a

lubricant’s viscosity change between 40°C (104°F) and

100°C (212°F). AMSOIL Severe Gear Synthetic 75W-90

Gear Lube provides a high viscosity index, allowing it to

protect against thermal runaway by maintaining its

superior viscosity protection in high temperature service.

Shear Stability

Many gear lubes are formulated with viscosity index (VI)

improvers in order to ensure multi-grade viscosity protection

in both hot and cold temperatures. VI improver

additives keep lubricants from becoming too thick to

flow in cold temperatures and too thin to protect in

high temperatures. However, shearing forces within

equipment can cause these additives to break down and

lose viscosity.

The CEC L-45-A-99 (KRL) 20-Hour Shear Test is a

requirement for all automotive gear lubes to ensure

they do not shear down and fall below minimum viscosity

requirements. The graph shows initial oil viscosity

and viscosity following the test, while the shaded

area indicates SAE J306 high-temperature viscosity

Viscosity Protection

Viscosity is the most important property of a lubricant

in its defense against friction and wear. Viscosity correlates

to film strength, and it is film strength that keeps

moving parts from contacting each other and creating

friction, heat and wear. The higher the viscosity of a

lubricant, the greater protection it provides. AMSOIL

Severe Gear Synthetic Gear Lubes are available in

75W-90, 75W-110, 75W-140, SAE 190 and SAE 250 viscosities,

each providing superior protection through

superior film strength

As gear and bearing loads increase, oil temperature

rises. As oil temperature rises, the oil becomes

thinner. When the oil becomes thinner, wear protection

is reduced and friction increases. As friction

and wear increase, the oil temperature rises further,

the oil becomes even thinner, and the friction and

wear increase again. This nasty cycle called thermal

runaway can ultimately lead to gear failure. AMSOIL

Severe Gear® Extreme-Pressure Lubricants are

shear stable. They maintain their protective

viscosity in the most demanding gear

applications. Break the cycle with

AMSOIL Severe Gear.

that seven gear lubes sheared down below the minimum

viscosity requirements for SAE J306. AMSOIL Severe

Gear 75W-90 tested in the proper initial viscosity range

and retained the highest viscosity of all tested oils after the

shear test, indicating its superior ability to protect against

thermal runaway by maintaining its protection qualities in

severe, high shear operating conditions.

The superior viscosity protection, viscosity index

and shear stability properties of AMSOIL Severe Gear

Synthetic Gear Lubes effectively protect equipment

from the devastating effects of thermal runaway. Severe

Gear Synthetic 75W-90, 75W-110 and 75W-140 Gear

Lubes are ideal for severe-duty applications, including

towing, hauling, steep hill driving, commercial use,

plowing, racing, off-road use, rapid acceleration,

frequent stop-and-go operation and high ambient

temperatures.

Severe Gear 75W-90 provides superior performance

and replaces competing 75W-90 and 80W-90 gear oils.

It delivers the best fuel efficiency and cold temperature

performance in the Severe Gear line.

Severe Gear 75W-110 provides superior performance

and replaces competing 75W-110, 75W-90 and 80W-

90 gear oils. It delivers better viscosity protection than

Severe Gear 75W-90 and better fuel efficiency than

Severe Gear 75W-140.

Severe Gear 75W-140 provides superior performance

and replaces competing 75W-140, 80W-140 and 85W-

140 gear oils. It is recommended where these viscosities

are required by OEMs and where maximum

viscosity protection is needed for extreme severe-duty

applications.

Severe Gear Synthetic SAE 190 and SAE 250 Gear

Lubes are formulated for racing and off-road applications,

including off-road truck racing, rock racing, rock

crawling, tractor pulling, funny car racing and dragster

racing. Other severe duty applications include heavy

duty trucks and equipment where increased lubricant

film is necessary.