Gl4 Vs. Gl5 Gear Oil : What are The Differences?

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. Talking about specifications, we have the GL class under the API grading, which introduces us to gl4 vs. gl5.

Many people want to know about the functionality of these two oils and if you can use them 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 gear lubricant showing you the designation of the product, which is 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 of this article, both GL4 and GL5 have EP additives, but the latter has more, translating to 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, and it aided in reducing the wear rate of gear sets. The result was an excellent performance of the transmission unit and enhanced durability.

However, the lead had adverse effects on the environment, leading to its phasing out in favor of a phosphorous and sulfur mixture. The combination creates a sacrificial coat on the gear’s metal surfaces, preventing abrasions and shock loads.

can i use gl4 instead of gl5

Read Also: 75w90 vs. 80w90: A Comparison of the Gear Oils

What Is GL4?

The designation of the GL4 oil is automotive that uses 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 transaxle use.

Gl4 vs. GL3; what is the difference? GL3 gear oil also serves spiral bevel gear systems, but it has a milder amount of EP additives than GL4. Can you use them interchangeably? You can use GL4 in GL3 systems to benefit from the former’s high load support and anti-wear capability.

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 behind its preference for high-speed and high-load applications. Its target is mainly 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 they have similar qualities. Gl5 vs. GL6 is another crucial comparison point. The GL6 is ideal for vehicles with high pinion offset hypoid gears, like 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 the former has more additives to boost its extreme pressure. The additives, in this case, are phosphorous 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, with the GL4 being 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 work in high-pressure conditions, though the latter has a high affinity to extreme-pressure surroundings.


Can You Use GL5 Instead Of GL4?

GL5 and GL4 have similar properties, and they have a decent amount of additives to enhance their extreme pressure rating. 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?

In the case of the GL-grade gear oils, we weigh the best as per their extreme pressure rating. GL5 oils rank top in extreme pressure due to their high sulfur and phosphorous. 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, transaxles, differentials, and transfer cases. The GL4 oil is versatile when you consider the many applications it has.

What Does GL4 Mean In Gear Oil?

Under API specs, we have the GL oils graded according to extreme pressure rating. GL4 is an oil grade, meaning gear lubricant at grade 4. This four means it has a decent level of additives in sulfur and phosphorous that increase its extreme pressure. The oil is among the top in extreme pressure rating, second to the 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 get corroded when exposed to elements like 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 like phosphorous and sulfur that enhance its performance. Look for the right gear oil retailer to get a befitting 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 understand that GL5 will do well in extreme conditions.

Is GL5 Yellow Safe?

Yellow safe refers to gear oils being non-corrosive to yellow gear metals, which feature copper, brass, and bronze. GL5 has sulfur and phosphorous 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 have sulfur and phosphorous additives for efficiency. Pick the right product for your gear according to the recommended specification by the manufacturer for extended service.

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Hi there, I am R. Hasan Tito, a mechanic, and owner of this website. My friend and I created this website to share our knowledge, expertise, and experience with our fellow mechanics' community and car users. I am a specialist and certified automotive mechanic (Both Heavy Commercial and Private Cars). I worked as a Mechanic and Mechanic Supervisor for over fifteen years at Global Rebound Automotive companies - Toyota, TATA, BMW, Nissan, TVs, and Others. Now, I enjoy my new role of leading a team of automotive experts (in their respective fields) and publish new content on a regular basis on my website and social media.

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