The American Petroleum Institute (API) has established a set of ratings to better distinguish between the unique physical and performance characteristics of different types of Gear Lubricants. Gearboxes and transmissions at work in heavy duty vehicles are subject to varying degrees of pressures, temperatures, and demands depending on make, model, and various other factors. Likewise, gear lubricants have unique specifications of their own - this potentially renders one exceptionally well-performing gear lubricant in one application useless or harmful in another.
API GL-4 automotive passenger car and light truck Gear Lubricants are intended for use in spiral-bevel and hypoid gears in automotive axles operated under moderate speeds and loads and may sometimes be implemented in select manual transmissions and transaxles. API GL-4 Gear Oils contain a milder level of extreme pressure (EP) additives which allows them to be used in broader applications. However, these lubricants are not intended for use in limited slip differentials or applications requiring an API GL-5 gear oil. Please consult OEM specifications to determine which type of lubricant performance category your vehicle requires.