Gear Oils
Gear Oil GL Ratings: From GL-1 to GL-5 Explained
GL ratings classify gear oils by their extreme pressure performance. Understanding the difference helps protect your gearbox and differential.
Gear oils are classified by the American Petroleum Institute using GL (Gear Lubricant) ratings. Each rating indicates the level of extreme pressure (EP) protection provided.
The GL Rating Scale
GL-1: Straight mineral oil with no EP additives. Used in older manual transmissions and axles operating under mild conditions.
GL-2: Contains mild EP additives. Designed for worm gear axles.
GL-3: Moderate EP protection. Used in manual transmissions and spiral bevel axles under moderate conditions.
GL-4: Good EP protection. The standard for most modern manual transmissions and transaxles.
GL-5: Highest EP protection. Required for hypoid gears in rear axles and differentials, especially under high-speed, high-torque conditions.
Choosing the Right GL Rating
Using a higher GL rating is not always better. GL-5 oils contain high levels of sulfur-phosphorus additives that can attack yellow metals (brass, bronze) found in some manual transmissions. Always follow the manufacturer's specification.
MB Lubricants' GEARLUBE range covers the full GL-1 through GL-5 spectrum, ensuring the right protection for every application.