GOOGLE is your friend !!! I googled "EP-GL5" and got all kinds of info. In particular, note the underlined & bolded statement under "Product Benifits" in the write-up (I underlined & bolded the sentence for emphasis:
Thuban GL5 EP
Description
Thuban GL5 EP oils are high performance, multipurpose, thermally stable, extreme pressure, automotive gear lubricants formulated with "clean gear" technology for applications where API GL-5/MT-1 performance is required.
They are available is SAE viscosity grades 80W-90 and 85W-140
RECOMMENDED FOR
Automotive hypoid gear differentials operating under high speed and/or low speed, high torque conditions
Heavy duty, non-synchronised manual transmissions and transaxles requiring this type of lubricant
Automotive steering gears
Top-up of limited slip differentials after break-in of new or rebuilt units
Thuban EP GL5 should not be used in manual transmissions and transaxles where the manufacturer recommends API GL-4 lubricants and advises against the use of API GL-5 lubricants.
PRODUCT BENEFITS
Reduced maintenance costs:
Special dispersant in the "clean gear" technology additive package suspends sludges and carbonaceous deposits in the gear oil, preventing their deposition on gear components and oil seals, thus avoiding the need for premature overhaul due to deposit induced seal wear or leakage. Outstanding thermal stability minimises the total amount of deposits that the dispersant has to deal with.
Extended gear equipment life:
High performance, sulfur-phosphorus EP additive system provides excellent load carrying capacity to protect gear equipment against surface distress (ie spalling, pitting, scoring and wear) under heavily loaded conditions. The special inhibitor system resists corrosion of copper alloys and ferrous metals.
Prolong oil service life:
Highly refined base oil and special inhibitor system provides excellent oxidation stability to resist oil degradation and thickening during long periods of severe high temperature operation.
PERFORMANCE CHARACTERISTICS
API: GL-5, GL-4
API: MT-1
Mack: GO-J
US Military: MIL-PRF-2105E
KEY PROPERTIES
SAE Grade 80W-90 85W-140
Density at 15°C, kg/L 0.903 0.909
Flash Point, °C 230 234
Pour Point °C -30 -15
Timken OK Load, kg 27 27
Viscosity, cSt at 40°C 140 344
Viscosity, cSt at 100°C 15.0 25.5
Viscosity Index 108 97
MSDS links click here click here
SERVICE CONSIDERATIONS
Modern automotive and heavy duty equipment places severe demands on gear oils. Heavier loads, diverse driving conditions, terrain and more aerodynamically designed body shapes have resulted in higher operating temperatures for differentials, transmissions and steering gear units.
At elevated gear oil temperatures, it has been found that many gear oils used in manual transmission and differential applications can allow sludge and hard carbonaceous deposits to form which cause oil seal wear, leading to leakage and premature equipment failure. Consequently, more thermally stable, "clean gear" oils are required to resist oil degradation and deposit formation.
Thuban GL5 EP is a thermally stable, "clean gear" technology gear oil, incorporating additional dispersant chemistry in its additive package to suspend any sludges and carbonaceous deposits which form, and prevent their deposition on oil seals, gears and critical yellow metal components of transmissions.
API MT-1 designates the type of service that is characteristic of non-synchronised manual transmissions, as commonly used in heavy duty equipment. Lubricants meeting the requirements of API MT-1 provide protection against the combination of thermal degradation, component wear and oil seal deterioration, which is not provided by lubricants that only meet the requirements of API GL-5.
ENVIRONMENT, HEALTH AND SAFETY
Click on the links in the table above to view the Material Safety Data Sheet (MSDS) for each product. Users should consult the MSDS, follow the precautions outlined and comply with all laws and regulations concerning its use and disposal. Used packaging material should not be incinerated or exposed to flame. After use, protect your environment. Do not pollute drains, soil or water with used product.
OTHER INFORMATION
For further information on Caltex products and services call the Lubelink Advisory Service on 1300 364 169 between 8.00 am and 6.00 pm (EST) Monday to Friday.
All reasonable care has been taken to ensure that the information contained in this publication is accurate at the time of printing. However, the information is liable to variation in the event of subsequent changes in the blend, formulation, method of storage, improper handling and usage etc.
