GL5

GL-5 is a performance designation for gear lubricants defined by the American Gear Manufacturers Association (AGMA). It applies to lubricants intended for enclosed gear drives that operate under high load, especially hypoid gear sets used in many automotive rear axles and in some industrial gearboxes.

GL-5 oils typically employ a high level of extreme-pressure EP additives, usually sulfur-phosphorus compounds, to form protective films under heavy load and reduce wear on gear teeth. This makes GL-5 formulations well suited to handling high torque and shock loads. However, the same EP package can be aggressive toward yellow metals such as brass or bronze and may be incompatible with some synchronizer assemblies in older transmissions. For this reason, GL-5 is not universally suitable for gearboxes that specify GL-4.

Common viscosity grades include 75W-90, 80W-90, and 85W-140, with both mineral-based and synthetic formulations available. They are widely used in automotive differentials with hypoid gears and in various industrial gearboxes. In some applications, limited-slip differentials require specific formulations or friction modifiers in GL-5 oils; in others, OEMs still call for GL-4 or a different specification.

Users should follow the vehicle or equipment manufacturer’s recommendation and avoid mixing GL-5 with GL-4 gear oils. GL-5 is a gear oil specification rather than a catch-all lubricant category and does not cover hydraulic or engine oil requirements.