- mroilguys
- Aug 15, 2023
- 0 min read
- mroilguys
- Aug 9, 2023
- 4 min read

You've probably heard of GL4 and GL5 gear oil if you're a car enthusiast. Whether you're changing your vehicle's gear oil for maintenance or upgrading its performance, understanding the differences between these two types of gear oil is critical. The composition, application, and performance of GL4 and GL5 gear oils differ.
In this comprehensive blog post, we'll delve into the six key differences between GL4 and GL5 gear oil and explore whether using GL-5 instead of GL-4 is possible. Furthermore, we'll discuss which one is more common and whether gear oil can go bad with age. So, buckle up and let's jump into the world of GL4 and GL5 gear oil.
What Is The Difference Between Gl4 And Gl5 Gear Oil: 6 Difference
Gear oil GL4 and GL5 have some key differences. Some of them are listed below:
1. EP Additive Levels and Performance
GL-5 gear oils have around twice as many EP additives as GL-4 gear oils to ensure optimal performance in high-speed, high-load applications like modern automotive axles. EP or extreme-pressure additives protect gear systems from wear and tear under heavy loads and high speeds.
These additives form a protective film on the metal surfaces, reducing friction and preventing metal-to-metal contact. As GL-5 gear oils contain a higher concentration of EP additives, they provide enhanced protection and lubrication, making them suitable for demanding applications.
EP additives make GL-5 gear oils more wear, scoring, and pitting resistant so they last longer.
2. Application Scope and Gear Type:
GL-4 gear oils are suitable for manual transmissions with moderate speeds and loads. They work well with spiral bevel and hypoid gears in car axles and spur/helical gears in manual transmissions.
On the other hand, GL-5 gear oils are specifically designed for hypoid gears in automotive axles that are exposed to demanding conditions, such as high-speed operations and heavy loads. If you have a manual transmission with moderate speeds and loads, GL-4 gear oil would be the appropriate choice.
However, GL-5 gear oil is better for hypoid gears in automotive axles subject to high speeds and heavy loads.
3. Protection:
EP additives reduce friction between gear surfaces, improving overall gear performance and efficiency. GL-5 gear oils contain higher levels of EP additives than GL-4, making them suitable for gears subjected to extreme stress.
Increased EP levels in GL-5 gear oils ensure superior protection, especially in high-pressure and high-temperature applications.
4. Compatibility and Limitations:
When using GL-5 gear oil, it's important to know its limitations and potential incompatibility with materials like bronze and copper. The sulfur/phosphorus additives in GL-5 formulations can react negatively with these materials. This reactivity can lead to corrosion and damage, making GL-5 unsuitable for use in gearboxes unless specifically allowed by the manufacturer.
On the other hand, GL-4 gear oils can be a more versatile option in certain applications. They can be used for hypoid gear service under severe conditions without shock loading. This means that GL-4 gear oils can provide enhanced protection without the risk of material incompatibility.
It's important to understand the specific requirements of your machinery and consult with the manufacturer to determine the appropriate gear oil for your needs.
5. Manufacturer Recommendations and Gearbox Suitability:
GL-4 gear oils are typically recommended for moderate-speed and load applications, while GL-5 gear oils are ideal for high-speed and high-load scenarios.
However, it's important to note that GL-5 gear oils may not be suitable for all gearboxes due to potential compatibility issues with certain materials. Therefore, following the manufacturer's recommendations is essential to ensure the correct gear oil is used for the specific gearbox.
Is it possible to use GL-5 instead of GL-4?
Although GL-5 and GL-4 gear oils may seem similar, they are not interchangeable. The main difference lies in each formulation's level of extreme pressure additives. GL-5 gear oils are designed for high-pressure applications and contain a higher concentration of additives to withstand the demands of heavy-duty gearboxes.
On the other hand, GL-4 gear oils have a lower concentration of extreme pressure additives and are suitable for less demanding applications, such as manual transmissions and light-duty gearboxes. The higher concentration of additives in GL-5 gear oil can damage synchronizers and other internal components in gearboxes that require GL-4.
It is always best to consult the manufacturer's specifications to ensure the correct gear oil is used for optimal performance and longevity of the gearbox.
What Is The Most Common Gear Oil Gl-4 Or Gl-5?
Based on the information provided, it is clear that GL-4 is the most common gear oil grade used in synchromesh gearboxes and transaxles. However, it is important to note that GL-5 gear oil is also available and may be used as a substitute for GL-4 in certain applications.
While GL-5 oils contain extreme pressure additives like GL-4 oils, they typically have a higher concentration. This makes GL-5 gear oil more suitable for heavy-duty applications like those found in trucks and SUVs.
Conclusion
As we come to a close, it is important to understand that the choice between GL4 and GL5 gear oil is not as simple as picking one over the other. GL5 gear oil provides better protection under high pressure and temperatures, making it ideal for heavy-duty applications.
Whereas GL4 gear oil is useful for older vehicles and manual transmissions requiring a lower friction modification level. The key takeaway is that it is always best to consult the manufacturer's recommendations before choosing between the two varieties.
Ultimately, the decision between GL4 and GL5 gear oil will depend upon your vehicle's specific needs.
- mroilguys
- Aug 9, 2023
- 4 min read

Gear oil is an essential factor for your vehicle's powertrain system, responsible for keeping the transmission and differential running smoothly and efficiently. But how often do you need to change your gear oil?
The optimal frequency for changing your gear oil depends on whether you're driving a manual or automatic gearbox. For manual transmissions, it's generally recommended to have an oil change every 30,000 to 50,000 miles (48,000 to 80,000 km). For automatic transmissions, oil needs to be changed every 60,000 to 100,000 miles (96,000 to 160,000 km).
In this article, we'll cover how to tell if it's time to change your gear oil, how easy it is, and even the color of bad gear oil and its tendency to thicken. So, look no further for all your gear oil change-related concerns.
How Do You Know If Your Gearbox Oil Needs Changing?

When determining if your gearbox oil needs changing, there are several key points to consider. Optimize machinery performance with premium gear oil from Mroilguy website. Ensure longevity and efficiency today!
1. Monitoring Signs of Poor Lubrication:
To ensure optimal performance, regularly checking for unusual noises is crucial in detecting signs of poor lubrication in your vehicle's gearbox.
By listening for grinding, whining, or clunking sounds during gear shifts or while driving, you can identify potential issues with insufficient lubrication in the gears. These unusual noises might indicate damage caused by the lack of proper lubrication.
It is important to pay attention to these signs as they can be an indication that your gearbox oil needs to be changed. If you notice any of these unusual noises, it is recommended to consider changing the gearbox oil to prevent further damage and maintain the smooth operation of your vehicle's transmission system.
2. Detecting Unusual Smells and Burning Odors:
If you notice any strange smells or burning odors coming from your vehicle's gearbox or differential, it could indicate potential issues with lubrication or oil leaks. These odors are often a result of poor lubrication or aging oil that has deteriorated over time.
Inadequate oil in the gearbox or differential can lead to increased friction and heat buildup, which can cause the oil to burn and emit a distinct smell. This burning odor serves as a warning sign that the lubrication is not functioning properly and may require immediate attention.
Note: To prevent further damage and ensure optimal performance, it is important to regularly change the gearbox oil and inspect for any leaks or worn seals.
3. Observing Gear Shifting Issues:
Experiencing slipping gears or jerky shifts could be a sign of gearbox issues. These symptoms can occur due to various factors, such as inadequate gearbox oil levels.
Before diving into complex diagnostics, it is crucial to check the gearbox oil levels. Inadequate oil can lead to compromised shifts, causing gears to slip or shift in a jerky manner. If the oil level is low, it is essential to address this issue promptly. Adding the correct amount of gearbox oil can often resolve the shifting issues.
However, if the problem persists even after ensuring adequate oil levels, further investigation may be required to identify and address the underlying gearbox issues.
4. Assessing Fluid Condition and Color:
If you've been experiencing gear shifting issues, the next step is to assess the condition and color of your gear oil. Over time, gear oil can accumulate deposits and contaminants, leading to degraded performance.
One telltale sign that your gear oil needs to be changed is a darkening color and a burnt smell. When the oil degrades, it becomes less effective at lubricating the gears, which can result in poor gear shifting and increased wear on the components. If the gear oil appears dark or burnt, it is a clear indication that it needs to be changed.
Is It Easy To Change Gear Oil?
Changing gear oil can be challenging without a car hoist, but it is still doable for experienced car fans with access to drain plugs. Gear oil replacement requires precision and attention to detail.
Firstly, gather the necessary tools such as a wrench, a drain pan, and the correct type and quantity of gear oil specified by the manufacturer. Locate the drain plug on the gearbox and position the drain pan underneath. Carefully remove the drain plug and allow the old gear oil to drain completely. Once drained, replace the drain plug and tighten it securely.
Next, locate the fill plug and remove it. Use a funnel to pour the new gear oil into the gearbox until it reaches the proper level. Replace the fill plug and tighten it.
What Is The Color Of Bad Gear Oil?
When your gearbox has been compromised, you'll notice that the color of the fluid is no longer pink, but instead brown or black. This change in color is a clear indication that there is a problem with your gear oil.
The normal color of gear oil should be pink, as stated by gearbox specialists. However, when the fluid turns brown or black, it suggests that there may be contaminants present or that the oil has deteriorated over time. These contaminants can include metal particles, dirt, or sludge, all of which can cause damage to your gearbox if left untreated.
Does Gear Oil Get Thicker Over Time?
As gear oil ages, it becomes thicker and can lead to various issues with the gearbox. Over time, the viscosity of gear oil increases, causing it to lose its ability to properly lubricate the gears and other moving parts. This increased thickness can result in increased friction, heat, and wear within the gearbox.
The thickened oil may also struggle to flow properly, leading to inadequate lubrication in certain areas. This can result in accelerated wear and tear on the gears, bearings, and seals, potentially causing premature failure of these components. Additionally, the increased viscosity can impede the gearbox's ability to transfer power efficiently, leading to decreased performance and decreased fuel efficiency.
To avoid these issues, it is essential to regularly change the gear oil according to the manufacturer's recommendations.
Conclusion
Many of us often overlook the importance of changing our gear oil, but it’s a simple and quick process that can ultimately save us money and keep our vehicles running smoothly. Not only does regularly changing your gear oil enhance the performance and longevity of your gearbox, but it can also prevent unnecessary wear and tear on the transmission.
Signs such as strange noises, gear shifting difficulties, or a burning smell should not be ignored and may indicate that it’s time for a change. Don't forget, contaminated or thickened gear oil can seriously affect your vehicle's performance, so follow the manufacturer's guidelines and change your gear oil periodically.