Gear Oils: Understanding the Differences
In the realm of gear oils, the American Petroleum Institute (API) has delineated specific Gear Load (GL) classifications:
GL-1: This classification refers to oils devoid of extreme pressure (EP) additives, typically containing fatty materials.
GL-2: This grade incorporates a mild EP additive.
GL-3: Similar to GL-2, but with enhanced properties.
-GL-4: Equivalent to MIL-L-2105B, generally satisfied by a 50% GL-5 additive level.
GL-5: Corresponding to MIL-PRF-2105E, this classification is the primary recommendation for field service in passenger cars and trucks worldwide.
GL-6: Designed for severe service applications involving high offset hypoid gears, this classification is often used to describe oils for limited slip differentials.
MT-1: Intended for non-synchronized manual transmissions in buses and trucks, offering a higher performance level than GL-3.
What Is GL-4?
The designation of GL-4 oil pertains to its application in automotive systems utilizing hypoid or spiral bevel gears. This oil is specifically formulated for vehicles operating at moderate speeds and loads, ensuring optimal performance for this utility. Depending on the brand, some GL-4 oils may be suitable for smaller vehicles, while others are versatile enough to accommodate both smaller and heavier vehicles. The primary application of GL-4 oil is in manual gearboxes and transaxles.
What Is GL-5?
GL-5 gear oil is distinguished by its exceptional extreme pressure rating, making it a preferred choice for high-speed and high-load applications. Its primary utilization is in hypoid gears within automotive axles. GL-5 can be regarded as an equivalent to GL-4 gear oil, albeit on a more extensive scale, serving as a viable substitute due to their analogous properties. A significant comparison exists between GL-5 and GL-6; the latter is particularly tailored for vehicles equipped with high pinion offset hypoid gears, such as those found in limited-slip differentials.
GL-4 vs. GL-5: Key Differences
The primary distinction between GL-4 and GL-5 lies in the incorporation of a greater number of additives specifically designed to enhance extreme pressure performance. These additives, particularly phosphorous and sulfur compounds, function by creating a sacrificial layer on gear surfaces, thereby mitigating degradation rates.
1. Application: GL-4 is designed for standard gears in manual vehicles operating at moderate speeds, whereas GL-5 is formulated for hypoid gears in automotive axles subjected to high speeds and loads.
2. Additive Levels: GL-4 contains up to 4.0% anti-scuffing additives, in contrast to GL-5, which includes up to 6.5%. This higher concentration in GL-5 enhances its performance under challenging conditions.
3. Red Line GL-4 and GL-5 gear oils contain copper deactivation compounds which make them suitable for yellow metal synchros.
4. Extreme Pressure Ratings: While GL-4 possesses a commendable level of extreme pressure additives, GL-5 is superior in high-load scenarios.
4. Performance: GL-5 oils are generally more suitable for high-performance applications due to their increased additive content, enabling them to withstand greater stress.
Understanding these differences is crucial for selecting the appropriate gear oil for specific applications.