Gear oils play a crucial role in keeping gear systems working efficiently. Different gear oils are formulated for specific applications, including GL-4 and GL-5. Understanding the difference makes sure the right oil goes into the right gearbox.
GL-4 gear oil
GL-4 gear oils are used in manual transmissions and transaxles. They provide effective lubrication and corrosion protection in moderate operating conditions. GL-4 oils contain a lower level of extreme-pressure (EP) additives than GL-5 oils, which makes them the safe choice for many manual gearboxes with synchronisers.
GL-5 gear oil
GL-5 gear oils are formulated for high-stress applications, especially hypoid gears in differentials and axles. They contain a higher level of EP additives and provide stronger protection against wear, scuffing and high-temperature oxidation under heavy loads.
Differences between GL-4 and GL-5
- EP additives: the main difference is the level of EP additives. GL-5 contains roughly twice as much, giving stronger protection under high loads.
- Yellow-metal compatibility: the high EP content in GL-5 can attack brass and bronze synchronisers in some manual gearboxes. Where a manufacturer specifies GL-4, GL-5 should only be used if it is explicitly approved as compatible.
- Operating conditions: GL-4 suits moderate conditions, while GL-5 is designed for high loads, high temperatures and shock loading, such as in differentials and heavy-duty axles.
- Performance: GL-5 offers greater protection for hypoid gears, while GL-4 protects synchronisers and yellow-metal parts.
Conclusion
GL-4 and GL-5 are not interchangeable. Always follow your vehicle or gearbox manufacturer's recommendation. Regular oil changes and proper maintenance will extend the life of your gear system and keep it performing at its best.
