Automotive gear oils serve as a specialized lubricant for transmissions, differentials, and other gear systems, minimizing friction, wear, and heat under high-pressure conditions. Proper selection is critical, as using an incorrect gear oil can result in accelerated corrosion, increased component wear, and premature system failure.
The American Petroleum Institute (API) created a classification system to assist users in selecting the proper gear oils. In this system, GL-4 and GL-5 are the two most common categories, each having unique characteristics and uses. This blog will examine the two categories in greater detail to clarify their differences and guide the selection of the most suitable option for specific operational needs.
What are GL-4 Gear Oils?
GL-4 gear oils are formulated for gear systems that operate under moderate pressure and speeds, such as spur and helical gears found in various machinery. They contain moderate levels of extreme-pressure (EP) additives, which effectively protect gears without being overly aggressive towards yellow metals like brass or bronze, commonly present in machine components. This balanced formulation ensures reliable protection while maintaining compatibility with sensitive materials commonly used in industrial equipment. However, it may be inadequate for extreme pressure applications and is therefore not recommended for heavily loaded or shock-loaded industrial gear systems.
What are GL-5 Gear Oils?
GL-5 gear oils are designed for heavy-duty gearboxes that encounter high loads, shock loading, and severe operating conditions. These oils contain a significantly higher concentration of sulfur-phosphorus EP additives, providing superior protection against extreme pressure and wear. However, this aggressive formulation can be corrosive to yellow metals like brass or bronze. Despite this, GL-5 oils are highly effective in applications where maximum EP protection is critical, provided the equipment’s materials are compatible with their strong additive package.
Key Differences Between GL-4 and GL-5
| Feature | GL-4 | GL-5 |
| EP Additives | Lower sulfur-phosphorus levels | Higher sulfur-phosphorus levels |
| Protection Level | Suited for moderate loads and speeds | Suited for high load, high speed, and shock conditions |
| Metal compatibility | Compatible for yellow metals (brass, bronze) | Can be corrosive yellow metals (brass, bronze) |
| Typical Use Cases | Spur and helical gears, moderate-duty gearboxes | Heavy-duty gearboxes, hypoid gears, shock-loaded systems |
The additive composition and intended application of GL-4 and GL-5 gear oils are the main distinctions between the two categories. GL-4 is safer for gearboxes with brass or bronze components since it has less extreme pressure (EP) additives. Although GL-5 provides better protection under stress and suits high-load systems like differentials, its aggressive additives can corrode brass or bronze components.
Common Myths and Misconceptions
Many people assume GL-5 is always superior due to its stronger protection, but this is not necessarily true for all applications. While it works well in high-load systems, it can damage manual transmissions with brass or bronze parts. A higher additive concentration does not necessarily translate to better performance, and the key consideration is meeting the specific operational needs.
Another common misunderstanding is thinking that all additives are safe. Some like the sulfur-phosphorus compounds in GL-5 can be excessively reactive for softer metals like brass or bronze. Over time, this can lead to corrosion and wear. It is essential to choose gear oils that are suitable for the components’ materials.
Protect Your Gears with the Right Oil – Choose Fluid Solutions
Understanding the difference between GL-4 and GL-5 gear oils is essential to keeping your equipment protected and performing at its best. At Fluid Solutions, we offer expert guidance and high-quality lubrication products tailored to your system’s specific requirements.Â
With personalized recommendations and proven solutions, we help you choose the right oil to ensure reliable performance and long-term protection for your machinery. For expert advice and dependable lubrication solutions, contact us on (02) 8370 5928 or (0917) 894 9156, or email us at inquiry@fluidsolutions.com.ph. You can also find more information and updates on our Facebook and LinkedIn pages.
