The transmission oil change is an essential practice for your vehicle, and you have to get a product with the correct specifications for your vehicle. Let’s talk about specifications: the GL class under the API grading introduces us to GL4 vs. GL5.
Many people want to know about the functionality of these two oils and whether they can be used interchangeably. We will provide more information about the oil types to help you navigate this topic.
What Does GL Stand For In Oil?
The starting point in the GL4 vs. GL5 discussion is deciphering the meaning of GL. It means the gear lubricant shows the product designation for the vehicle’s gear unit. Under the GL class, you find other oil types with numbers from 1 to 6.
The GL1 oil does not have any EP additives. EP stands for extreme pressure, and the additives improve the oil’s performance in different conditions. GL2 oil has fatty materials, while GL3 contains mild EP additives.
On to the main players in this article: both GL4 and GL5 have EP additives, but the latter has more, resulting in a better EP rating. Finally, you have GL6, which is suitable for high-offset hypoid gears.
What is the benefit of additives? Some time back, lead was the main additive in gear oils, helping reduce gear set wear rates. The result was excellent transmission unit performance and enhanced durability.
However, the lead had adverse environmental effects, leading to its phasing out in favor of a phosphorus-sulfur mixture. The combination creates a sacrificial coat on the gear’s metal surfaces, preventing abrasions and shock loads.
Read Also: 75w90 vs. 80w90: A Comparison of the Gear Oils
What Is GL4?
The GL4 oil designation is automotive, used in vehicles with hypoid or spiral bevel gears. The vehicles have moderate speeds and loads for this utility to perform optimally. Depending on the oil brand, some may work with smaller vehicles, while others are multipurpose, serving both smaller and heavy vehicles.
The target of GL4 is mainly manual gearboxes and transaxles.
Gl4 vs. GL3; what is the difference? GL3 gear oil also serves spiral bevel gear systems, but it has fewer EP additives than GL4. Can you use them interchangeably? You can use GL4 in GL3 systems to benefit from its high load support and anti-wear capabilities.
What Is GL5?
Flipping the coin of this discussion, we bring you the GL5 gear oil. It has an extreme pressure rating, which is one of the reasons it is preferred for high-speed, high-load applications. Its target is mainly the hypoid gear in automotive axles.
You may consider the GL5 a GL4 gear oil equivalent, though on a larger scale. You can use it as a replacement for GL4, as it has similar properties. GL5 vs. GL6 is another crucial comparison point. The GL6 is ideal for vehicles with high-pinion offset hypoid gears, such as those in limited-slip differentials.
The MIL-PRF-2105E is a military-grade GL5 released sometime in the mid-1990s. It is mainly for use on military vehicles.
Gl4 vs. Gl5 Differences
The main difference between GL4 and GL5 is that GL4 has more additives to boost its extreme-pressure performance. The additives, in this case, are phosphorus and sulfur compounds. They help by providing a sacrificial layer on the gear surfaces to reduce their degradation rate.
The other contrasting point is their use: the GL4 is suitable for severe hypoid gear service without the shock-loading factor. On the other hand, you use the GL5 for high-service hypoid gear with shock loads. Plus, it is not for use on the gearbox. GL4 and GL5 operate under high pressure, though the latter has a high affinity for extreme-pressure environments.
FAQs
Can You Use GL5 Instead Of GL4?
GL5 and GL4 have similar properties and include a decent amount of additives to enhance their extreme pressure ratings. You can use GL5 instead of GL4, though it does not mean you should. For the best performance of your vehicle’s transmission system, use the recommended oil type.
Which Is Better, GL4 Or GL5?
For GL-grade gear oils, we weigh them based on their extreme pressure rating. GL5 oils rank high in extreme pressure due to their high sulfur and phosphorus content. The fact that you can use it in place of GL4 oil shows that it is the best in its category.
Can I Use GL4 in Differential?
The differential is a set of vehicular gears that sends power from the engine to the wheels. For the differential to work effectively, you need to oil it. GL4 does an excellent job on gearboxes, transmissions, differentials, and transfer cases. The GL4 oil is versatile, with many applications.
What Does GL4 Mean In Gear Oil?
In the API specs, we have GL oils graded according to their extreme pressure rating. GL4 is an oil grade, meaning it is a gear lubricant grade 4. This four indicates it has a decent level of additives in sulfur and phosphorus, which increase its extreme pressure. The oil is among the top in extreme-pressure rating, second only to GL5 oil.
Is GL4 Yellow Metal Safe?
Yellow metals refer to copper, bronze, and brass, which you find in low-load systems, such as in motorcycles. A downside of yellow metals in gears is that they can corrode when exposed to elements such as sulfur. You may find traces of metals in the oil. GL4 has sulfur, intended to improve its wear resistance. However, the same compound will corrode yellow metals.
Is GL5 Synthetic?
Synthetic oils offer excellent service to your gear and are generally clean. The GL5 oil has synthetic versions with mineral additives, such as phosphorus and sulfur, that enhance its performance. Look for a reputable gear oil retailer to find a suitable product for your car.
What Weight Is GL5 Gear Oil?
Most of the time, you will find GL5 oil with a weight of 80W-9. This weight code shows you its thickness in different conditions. The 80 is the oil’s thickness in winter conditions, and the 90 is 100 degrees Celsius. Looking at its performance figures, you can see that GL5 will perform well in extreme conditions.
Is GL5 Yellow Safe?
Yellow safe refers to gear oils that are non-corrosive to yellow gear metals, which include copper, brass, and bronze. GL5 has sulfur and phosphorus additives to increase its extreme pressure rating. Sulfur corrodes the yellow metal; thus, GL5 is not yellow-safe.
Final Word
When getting gear oil for your car, it is prudent to check the specifications to ensure that you have the right product. In the GL4 vs. GL5 discussion, we learned that the oils contain sulfur and phosphorus additives to improve efficiency. Pick the right product for your gear based on the manufacturer’s recommended specifications for extended service.
Learn More:
