Gear Lubricants
Background & Properties
castrol.com/GPS
800 255 4417
May 2025
GPS
Industry Specifications
Oil Compatibility and Solubility (FTM 3430 and FTM 3440)
Same test and limits as API GL-5 gear lubricants.
Oil Seal Compatibility (Similar to ASTM D 471)
A test not required for API GL-5 gear lubricants. Measures the change in volume, hardness and elongation of
oil seals for API MT-1 lubricants.
Test Limits
Polyacrylate
Elongation change -60 to 0%
Hardness change -20 to +5 pts
Volume change -5 to +30%
Fluoroelastomer
Elongation change -75 to 0%
Hardness change -5 to +10 pts
Volume change -5 to +15%
Anti-wear Characteristics (ASTM FZG D 5182)
Another test not performed on API GL-5 lubricants, ASTM FZG D-5182 determines a lubricant's anti-wear
strength.
Test Limit
Min 10 stage pass
High Temperature Stability (Mack Transmission Test T2180)
Performed only on API MT-1 lubricants, the Mack Transmission Test T-2180 evaluates the oil's thermal stability
during extreme high temperatures.
Test Limit
Equal to or better than reference oil
ere is increasing concern from OEMs regarding the operating temperatures API GL-5 lubricants must
consistently face. API MT-1 was the result of an update to the API GL-5 category as spurred by heavy-duty
equipment builders.
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