Standard-CLP stands for the minimum standard which, however, especially with gear oils, can be surpassed by the producer. The number after the designation CLP (e.g. 220) stands for the viscosity level. CLP- gear oils are subdivided into mineral-based and synthetic CLP. Synthetic gear oils are subdivided into polyalphaolefin(PAO) based and polyglycol (PG) based oils. Attention! CLP PG gear oils cannot be mixed with other mineral, Ester or PAL-based oils! Synthetic gear oils are not necessarily better than mineral based oils. It depends on the gear type and the application situation.
Often, specifying a gear oil for an end user is as simple as following an OEM recommendation. This should always be the first step in identifying the proper gear oil to use. This information will either be found directly on a nameplate of the gearbox or contained in a lubrication chart in the maintenance manual/
user guide for the respective make and model of the gearbox. OEMs use several standards to define the desired performance characteristics and the type of the oil for a given application, temperature range or operating condition. The following is a brief overview to explain a few of the standards used in the gear oil industry.
Viscosity of a gear oil is one of the most important physical characteristics to be considered. With so many different international standards defining viscosity requirements, the International Standards Organization Viscosity Grade (ISO VG)
was developed with input from all international organizations.
This ISO system is used to minimize confusion between equipment anufacturers, end users and lubricant suppliers by standardizing the different viscosity grades of an oil. The ISO VG is defined as the base oil’s viscosity expressed in the unit centistoke (cSt), which is also equal to mm2/s at a standard temperature of 40°C. There is an allowable tolerance of +/- 10% of that standard viscosity grade. For example the viscosity of an ISO VG 460 oil is acceptable at a minimum of 414cSt at 40°C and a maximum of 506cSt at 40°C. ISO viscosity grades can vary from an ISO VG 2 up to ISO VG 3200 and are defined in standard steps in between.
The API specification is written by the Lubricants Group of the American Petroleum Institute and is developed to assist automotive manufacturers and end users in the proper selection of transmissions, transaxles and axle lubricants. The test requirements are defined by ASTM D7560 and ASTM D7450.
While the API designation is primarily focused on automotive products, there still are a few OEMs that will use this for industrial applications. Currently there are only three API designations that are used.
These are API GL-4, API GL-5, and API GL MT-1.
• API GL-4: Intended for use in applications with spiral bevel gear sets that operate under moderate to severe conditions.
• API GL-5: Intended to be used in hypoid gears that are operating under high speeds and shock loading, or under low speed and high-torque conditions. This is defined in ASTM D7450.
• API MT-1: Denotes lubricants that are intended for use in non-synchronized manual transmissions. They are specifically designed to perform under the operating conditions and on the components in a manual transmission. This is specifically true for the compatibility of sealing materials.
API GL-1, API GL-2, API GL-3, & API GL-6: These four designations are all not currently in use due to the ever-changing application and test requirements. They may still be listed by a manufacturer or OEM, but in the situation, they are the API Designation document should be checked to provide a current and accurate lubricant recommendation.