Product Families

Gear Oils


Gears are the most common way to transmit power from one revolving shaft to another. Different combinations of gears may be responsible for increasing speed, decreasing speed, increasing torque, changing the direction of the shaft, and/or adjusting the angle between the input and output shafts. Gears are usually found in meshed pairs; the smaller gear is called the pinion and the larger gear is called the bull gear, ring gear, or just simply “the gear”.

Due to varying needs and applications, there are several types of gear. A basic knowledge of the most common types of gear, their components and methods of operation is helpful in understanding which lubricant will enhance gear performance. Below are some of the types gear encountered in today’s equipment. Each gear is typically named after its general shape or by the arrangement of its teeth.

Product Range Available Viscosities 1 Performance Additives 2 Base Oil Typical Viscosity Index Upper temperature guide for normal operations 3 Description and Application
Molub-Alloy GM Range EP/Solids Mineral - 82°C/180°F Heavy duty load and shock loading.
Molub-Alloy GM 170W 680 Compounded/Solids Mineral 97 82°C/180°F Heavy duty load and shock loading, especially for worm gears
Optigear 1100 Range MFT-PD Mineral 95 88°C/190°F MFT - PD oil, low friction, surface protection and gearbox life extension
Optigear BM Range MFT-PD Mineral 95 88°C/190°F MFT - PD oil, low friction, surface protection and gearbox life extension, with Flenders approval, can be used for worm gears
Optigear EP Range MFT-PD + EP Mineral 95 88°C/190°F As Optigear BM + High loading (API GL5-FZG scuffing load carrying), where boundary and mixed friction can occur.
Optigear Synthetic X 220, 320, 460 MFT-PD PAO >150 100°C/212°F MFT- PD, used in Wind Industry, for surface protection, long life and wide temperature fluctuations.
Optigear synthetic CT 220, 320 EP PAO >150 100°C/212°F Enhanced conventional type, used in Wind Industry, for surface protection, long life and wide temperature fluctuations.
Optigear Synthetic PD...ES Range MFT-PD PAO >150 100°C/212°F MFT - PD for surface protection, long life and wide temperature fluctuations, with Flenders Approval.
Optigear RMO 150 MFT-PD + EP PAO 133 100°C/212°F High load carrying, automotive type additives for railroad gearboxes
Optigear Synthetic 800 Range EP/AW PAG >200 120°C/248°F High Temperatures, low friction especially for worm gears

What are the different types of Gear?

Spur Gear

  • Have straight teeth that are parallel to the axis
  • Drive parallel and non-intersecting shafts
  • Are used in slow-speed industrial applications

Helical Gear

  • Have teeth that are cut at an angle to the face of the gear
  • Drive parallel and non-intersecting shafts
  • Are used for high-load applications (e.g. rolling mills)

Double Helical Gear

  • Are like a side-to-side combination of two helical gears, having teeth with opposing angles; also known as herringbone
  • Run without any end thrust

Bevel Gear

  • Tooth-bearing faces are conically shaped
  • Are used to transmit power between two shafts whose axes intersect

Spiral Bevel Gear

  • The teeth of an ordinary bevel gear can be twisted to form a spiral bevel gear. The spiral appearance results from cutting angled teeth into a cone-shaped gear
  • The angled teeth allow for a quiet, smooth transfer of power and strong gear system

Worm Gear

  • Are made up of two parts: the worm and the wheel
  • Offer the smoothest, quietest form of gearing
  • Provide high-ratio speed reduction and take up minimal space

Hypoid Bevel Gear

  • Resemble bevel gears, except that the shaft axes do not intersect
  • Have spiral teeth that are curved and oblique
  • Are not commonly found in industrial applications

typical wind gear type

Epicyclic (Planetary) Gear

  • Epicyclic (or planetary) gearboxes are slightly different. They give a higher gear ratio in a smaller space
  • Can be used for increasing speed (slow input, fast output); ind turbines do this
  • Are most commonly found in wind gearboxes, and can also incorporate more than one planetary gear stage as well as a helical gear stage
  • "Winning in the Wind Sector" is a separate training module that covers more in this area

Hpl mineral gear oils

HPL Mineral gear oils with mft-pd

HPL OptigearTM gear oils are based on MicrofluxTrans Plastic Deformation (MFT PD) technology to improve friction surfaces to an extent not possible with normal machining processes and conventional EP lubricants. These additives instantaneously create a passive film on metal surfaces before friction occurs. Under severe load, components of the additive combination are activated and diffuse into the metal surfaces, initiating an improvement of their frictional characteristics through plastic deformation. This unique physio-chemical reaction achieves a non-sacrificial micro-smoothing of the friction surfaces that provides optimum wear protection and an extremely low coefficient of friction even under extremes of pressure, vibration, shock loads and varying speeds.

More details on MFT PD can be found in the Technical Information section.

There are many examples of case studies where HPL gears oils have demonstrated significant performance benefits over conventional gears oils. Here are some examples:

  • Extending Gearbox Life
  • Company: Alcoa
  • Product: Castrol Optigear BM 460 replaced GR-XP 460

Evaluation before Castrol:

  • Gear teeth had been showing wear on six-monthly inspections
  • Temperature of gearbox had been steadily increasing
  • There was a need to introduce a new oil to reduce temperature and extend the life of the gearbox


  • To prove that the introduction of a new oil could halt teeth wear, extend the life of the gearbox
    and reduce the elevated temperature

Evaluation with Castrol:

  • Temperature was reduced by 10ºC within four hours of operation
  • Gear teeth wear stopped
  • There was a need to introduce a new oil to reduce temperature and Gearbox life has been extended
  • Total savings: $50,000
  • Extending Maintenance Intervals
  • Industry: Integrated steel mill
  • Machine: KOBM Tilt Drive Gearbox

Issue: The KOBM tilt drive gearbox had given the engineering group problems for many years. Gear wear was evident; analysis showed high metal wear, requiring repairs to the gears. To change the gearbox would require a five-to-seven-day closure of the continuous plant. Shell originally supplied Omala 320 then moved to Omala 460; Omala 680 was being used when Castrol became involved

Solution: Castrol recommended Optigear BM 680 for this gearbox

Result: The use of Castrol Optigear BM 680 stopped the build-up of wear metals and provided enough gear repair to allow the gearbox to run to its next scheduled change (extended to 12 months)

  • Total savings: $100,000
  • Reducing Frequent Breakdowns
  • Company: Vale
  • Product: Castrol Optigear BM 320 replaced conventional gear oil
  • Machine: Renk Zanini Reducer

Evaluation before Castrol: Low reliability due to early wear of gears; useful life of reducer was 48 days

Challenge: To prove that the introduction of new oil could halt wear and extend the life of the gearbox

Evaluation with Castrol: Temperature was reduced by 35% as shown in the images below, with actual temperatures on the images. There was a significant increase in reducer life to two years



  • Total savings: $54,000

HPL Mineral Gear Oils with Lubricating Solids

The Castrol Molub-AlloyTM GM range is based on solid-film lubricants containing special blends of micron-sized and submicron-sized lubricating solids to enhance the performance of premium-quality oils and greases. Solid-film lubricating technology exploits both the friction-fighting laminar physical structures as well as the bivalent, trivalent and quadrivalent chemical bonds that characterise a broad range of solid lubricating materials. Castrol’s Molub-Alloy range has been developed using synergistic combinations that offer load-carrying, friction-reducing and anti-wear performance over a broad range of industrial operating temperatures and pressures.

More details on lubricating solids can be found in the Technical Information section.

Castrol Molub-AlloyTM GM 969/320 is another product in the Castrol Molub-Alloy GM range, based on the same lubricating solids but with the addition of a synthetic thickener that coagulates at the point of oil loss to stop the leak. At the point of lubrication on the gears, however, it acts like other Castrol high-performance gear oils to provide long-term wear protection.

In one case study at a steel mill, Castrol Molub-Alloy GM 969 eliminated shaker gearbox failures that previously had leaked incessantly.

HPL Mineral Gear Oils with Lubricating Solids_10Maintenance totalLube costMake-up costParts cost$20,000$10,000$30,000$40,000$50,000$60,000$70,00064,19055,1205,07065004,000Before CastrolAfter Castrol

Above: Cost savings associated with use of Castrol Molub-Alloy GM 969 in steel mill shaker gearboxes. Due to the heavy vibrations, seals were continually damaged and could not be fixed often enough to prevent large oil losses. After conversion to Castrol Molub-Alloy GM 969, oil loss was greatly reduced and gearbox failure was eliminated.

HPL synthetic gear oils

Castrol’s synthetic gear oils are specially engineered to handle extreme conditions, with enhanced features such as thermal stability, high load-carrying capacity, extreme pressure resistance, high viscosity index and wide temperature range. Each of the specially engineered synthetic gear oils is based on either a polyalphaolefin (PAO) or polyalkylene glycol (PAG) base and blended with additives to offer a unique technology for a specific application.

HPL Synthetic (pao) gear oils with MFT-PD

Similar additive system to HPL mineral gear oils with MFT PD but with the additional benefits of synthetic base oils, including:

  • Increased oil life compared with mineral oils
  • Better viscosity profile at high and low temperatures

More details on MFT PD can be found in the Technical Information section.

  • Gearbox life extension
  • Prolonged Oil Life and Reduced Micropitting Helps to Extend Gear Life in Wind Turbine Gearboxes
  • Wind energy producer in Denmark

The Situation

A wind farm owner in Denmark using a mineral gear oil in its 600kW wind turbines was experiencing performance issues with the current gear oil, leading to downtime and high maintenance costs.

Before Castrol

  • The gear oil being used caused micropitting on the gears, leading to gearbox failure and downtime
  • Residue formation caused a build-up on gearbox walls
  • High foam was present
  • Oil lasted less than two years

Using Castrol Optigear Synthetic X

  • Castrol Optigear Synthetic X exceeded expectations by extending gearbox life, prolonging oil life and saving countless hours of downtime
  • Residue formation was eliminated
  • No foam presence was detected
  • Excellent load-carrying performance was achieved in the gearboxes
  • Testing of the oil after two years in service shows the gear protection performance remains equal to the new oil
  • Oil life was extended by a minimum of 50%; the expected oil lifetime is 3+ years with the potential to run much longer
  • Gearbox protection
  • Newly launched Optigear Synthetic PD ES range
  • Benefits include:
  • Reduced micropitting; gears running more reliably
  • Reduced energy consumption
  • Lower friction, so lower running temperature
  • Oil and equipment lasting longer
  • Problem-solver
  • Lower noise

Refer to launch information for more details.

Gearbox protection-30%

Lower Frictional Torque1
and superior surface protection2
than commercially available gear oils

HPL synthetic (PAO) Gear Oils with Enhanced EP/AW System

Conventional lubricants containing EP/AW (Extreme Pressure/Anti-wear) additives protect friction surfaces by means of soft metallic or oxide layers. These prevent direct contact between the friction surfaces, but are removed by mechanical load so have to be renewed again and again. Some reaction products can cause a premature ageing of the lubricant, and chemically active EP additives can react with yellow metals.

To combat the disadvantages of this type of technology when used in HPL fluids, the amount of additive has been significantly increased. This retains the advantages of this type of technology, which are compatibility with other fluids and low water content.

More details on EP/AW technology can be found in the Technical Information section.

  • Reduced maintenance interventions
  • Castrol Optigear Synthetic CT 320 has up to 30% less foam than other conventional gear oils, helping to prevent trips and unnecessary tower climbs. Three-and-a-half years’ field-trial experience and extensive lab tests have helped to deliver and prove enhanced gearbox protection.

Castrol Optigear Synthetic CT 320 has been helping a major wind turbine manufacturer’s turbines for over seven years now.


PAG synthetic lubricants, such as the Castrol Optigear Synthetic 800 range, are unique in many ways and include the following benefits over other oil types:

  • Very high viscosity index (VHVI)
  • Low coefficient of friction
  • Excellent thermal stability
  • Improved gearbox efficiency
  • Lower gearbox temperatures

The VHVI of these lubricants permits them to be used in extremely low temperatures and wide temperature ranges, often allowing for lubricant viscosity grades to be consolidated. When heated, the viscosity with the original lubricant is maintained more closely, providing greater oil film than other lubricants at elevated temperatures. The low coefficient of friction reduces the energy consumption, lowers the gearbox temperature, and increases the efficiency of the gears. This is particularly observed in worm gear drives, where efficiencies are typically much lower than other gear sets.

Viscosity-temperature relationship of various lubricants

Asset 225100120140160180200Temp (°F)Viscosity (cSt)250PAG (ISO 320)PAO (ISO 320)Mineral (ISO 320)

Above: The viscosity of oils drops with temperature, but PAG oils maintain viscosity better than mineral oils and other synthetics. At 104˚F, all of these lubricants have a viscosity of 320cSt, but at 200˚F, the mineral oil and PAO are much lower in viscosity than the PAG (Castrol Optigear Synthetic 800/320).


Example: In one case study at a steel mill, Castrol Optigear Synthetic 800 eliminated worm gear failures on castor withdraw roll and straightener gearboxes. The previous PAO oil could not maintain proper film strength at the high temperatures (>200˚F), resulting in 10 failures per year.

Annual cost comparison

annual-cost0Fluid costEquipment costDowntime costTotal annual costAnnual savings$50,000$100,000$150,000$200,000$250,000$300,000$256,970Previous PAOCastrol Optigear Synthetic 800

Above: Case study in steel mill worm gear drives on castor withdraw rolls and straighteners. The previous PAO lost film strength at the working temperature of over 200˚F, resulting in 10 failures per year. Castrol Optigear Synthetic 800 maintained exceptional film strength and eliminated all failures.

Open gear oils

For details, refer to the Open gear oils and greases section of this document.

Food-grade gear oil

For details, refer to the Food-Grade oils and greases section of this document.