A Guide to Gear Oils

The selection of a gear oil for any application must take into consideration Load and pressure on the gears, the rotational speed of the gears and the ambient conditions the gears will be used in.

Basic Functions

The basic functions of a gear oil are to:

  • Prevent metal to metal contact
  • Reduce wear
  • Dissipate heat
  • Reduce friction, shock and noise between gears
  • Carry additives
  • Flush contaminants from metal contact area
  • Prevent corrosion
  • Assist in protecting gears against pitting
  • Demulsify water
  • Assist in protecting against metal transfer

Castrol Branded Gear Oils

Alpha SP                General Purpose Gear oil

Castrol HSR            Heavily Fortified Gear oil

Castrol HSG             Molybdenum di sulphide additive

Optimol BM             Micro flux trans technology

Tribol                      Hi load extreme pressure Synthetic 

Molub Alloy             Hi load mineral and synthetic oil

Alphasyn                Synthetic extreme pressure

Optisyn                  Synthetic high temp gear oil

Unilube BG              Open gear lubricant

This information has been sourced, reviewed and adapted from materials provided by Castrol.

For more information on this source, please visit Castrol.


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