Automotive gear oils protect gears, bearings and cross-shafts from premature failure, ensure reliable equipment operation and increase transmission and differential service life. Automotive gear oils achieve this by performing the following five vital functions:

• Reducing friction and wear
  An oil film of a certain thickness must be maintained between gear teeth at all times to prevent metal-to-metal contact between gear surfaces under extreme pressure conditions. Hypoid gear drives are especially tough systems to lubricate, since the gear contact motion severely shears the oil with sliding as well as rolling motions and the gears are severely shock loaded.

• Providing oxidation stability
  A gear oil should resist thermal degradation and sludging so that harmful viscosity increase is minimized over time.

• Cooling the gear surfaces
  Gear components are prevented from destructive over-heating, by circulating oil through the gear mesh zones, where frictional heat is generated.

• Inhibiting rust and corrosion
  A gear oil must be non-corrosive to bronze, and protect steel surfaces against rust, especially when water contamination is present.

• Maintaining long clutch life and preventing seal leaks
  Clutches used in wet brakes and manual transmissions can become “glazed” and lose their function, if gear oils decompose at high temperatures. Gear oils must, therefore, be thermally stable.Undesirable decomposition products can also coat seals with carbon, causing leakage.