Gear Lubricants
Background & Properties
castrol.com/GPS
800 255 4417
May 2025
GPS
Industry Specifications
API GL-5
e mechanical tests required for API GL-5 gear lubricants are as follows:
Load Carrying (ASTM L-37)
is low speed/high torque test determines the load-carrying ability of the lubricant. Extreme pressure
additives are needed to pass this test.
Test Limit
No tooth disturbance, such as pitting, ridging, rippling or severe wear
Corrosion Resistance (ASTM L-33-1)
Corrosion resistance in the presence of water is determined by this test. e gear lubricant must protect a
surface against rust aer 7 days of water exposure.
Test Limit
No rusting aer 7 days on any working surface Max .5 in rust on cover plate
(1% of surface area)
High-Speed Shock Loads (ASTM L-42)
e ability to prevent scoring under high-speed shock load conditions is measured by ASTM L-42.
Test Limit
Gear/pinion scoring must be equal to or better than RGO-110
ermal and Oxidative Stability (L-60-1)
L-60-1 measures base oil quality, additive component and thermal and oxidative stability.
Test Limit
100% max viscosity increase
3% max pentane insolubles
2% max toluene insolubles
Anti-foam Properties (ASTM D 892)
e oil's ability to resist foam is determined aer 5 minutes of aeration during the ASTM D 892.
Test Limit
Sequence I 20 ml, max
Sequence II 50 ml, max
Sequence III 20 ml, max
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