Gear Lubricants
Background & Properties
castrol.com/GPS
800 255 4417
May 2025
GPS
Industry Specifications
Copper Corrosion (ASTM D 130)
Corrosion levels are taken on copper components aer a specified time interval and under strict temperature
conditions in ASTM D 130.
Test Limit
3 max aer 3 h at 121.1°C
Oil Compatibility and Solubility (FTM 3430 & FTM 3440)
Evaluated by FTM 3430 and FTM 3440 respectively, an oil must show minimal separation of material and
continue to maintain solubility aer being mixed with different reference oils.
Test Limit
FTM 3430: 0.25% wt max or original nonpetroleum material in sample
FTM 3440: 0.50% wt max of original nonpetroleum material in sample
API MT-1
API MT-1 was designed as a specification for transmissions apart from API GL-4. It provides additional
protection against thermal degradation, component wear and oil-seal deterioration versus API GL-4 and API
GL-5 lubricants. e test requirements for API MT-1 lubricants are as follows:
Copper Compatibility (ASTM D 130)
Measured by ASTM D 130, API MT-1 lubricants have a stricter corrosion limit than API GL-5 lubricants.
Test Limits
2A max aer 3 h at 121.1°C
Foam Resistance (ASTM D 892)
Same test and limits as API GL-5 lubricants.
ermal and Oxidative Stability (L-60-1)
Same test and limits as API GL-5 but with added measurements for component cleanliness as shown by
carbon and sludge deposits.
Test Limits
7.5 min carbon/varnish rating on large gear
9.4 min sludge rating on all gears
E7
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