Can You Use GL-5 Gear Oil Instead of GL-4?

Let’s say you’re out of GL-4 gear oil and the store is all out. Can you substitute GL-5?

If you can’t find GL-4 or if GL-5 is the only option, using GL-5 is better than using no oil at all. But the question is; can you use GL-5 gear oil instead of Gl-4?

It is a little bit challenging to answer, especially if you don’t have a clear idea of these gear oils and their differences. But don’t worry; we’re here to help you.

In this article, we will try to know if is it possible to use GL-5 gear oil instead of GL-4 or not. So why late? Let’s get started with it.

gl4 vs gl5

What Does GL Stand for in Oil

When you’re shopping for gear oil, you’ll likely come across two different types: GL-4 and GL-5. So, what does GL stand for in oil?

GL stands for gear lubricant. The 4 and 5 in GL-4 and GL-5 refer to the viscosity of the oil. The higher the number, the thicker the oil. GL-4 is thinner than GL-5, so it’s better suited for lighter applications like motors with smaller gears.

GL-5 is thicker and better suited for heavier applications, like motors with larger gears. It can also withstand more heat and pressure. That’s why it’s the preferred choice for most vehicles.

What is GL-5 Gear Oil

GL-5 gear oil is a product that is designed to lubricate gears in heavy-duty equipment. It is a synthetic oil that is manufactured to provide superior performance in extreme conditions.

It is designed for use in heavy-duty transmissions, differentials, and other gear-driven applications. GL-5 is formulated with additives that help protect against wear, rust, and corrosion.

This gear oil is not recommended for use in applications where an oil with an extreme-pressure (EP) additive is required.

What is GL-4 Gear Oil

GL-4 gear oil is a special type of lubricant designed for use in manual transmissions and differentials. It is made with a higher viscosity than other gear oils, which helps it to better protect gears and bearings from wear. GL-4 gear oil is also designed to be compatible with brass and bronze components.

While GL-4 gear oil can be used in many different types of manual transmissions and differentials, it is not suitable for use in all applications. For example, GL-4 gear oil should not be used in applications where there are high levels of friction, such as in limited-slip differentials. It is also not recommended for use in wet-clutch transmissions.

See: Can I Use Motor Oil For Transmission

The Difference between GL4 Vs GL5

The main goal of this article is to know if can you GL-5 gear oil instead of GL-4 or not. This is why we try to compare between these two gear oils. It will help you to know which is the better one.

EP Additives

When it comes to EP additives, GL4 oils have a lower dosage of additives than GL5 oils. This is because GL5 oils are formulated to protect gears against severe conditions, while GL4 oils are meant for less severe conditions. In most cases, GL4 gear oils do the job just fine. However, if you’re in a particularly severe environment, you may want to go with a GL5 gear oil instead.

EP additives are important because they help protect your gear from wear and tear. They work by coating the gear teeth with a thin film that acts as a shield between the teeth and the metal. This prevents them from coming into contact with each other and keeps them from wearing down.

As a general rule, GL4 oils should be used in applications where the gear temperature does not exceed 250 degrees Fahrenheit. If you exceed this limit, you may want to consider using a GL5 oil instead.

EP Protection

API GL-4 oils are not recommended for gearboxes that require extreme pressure and EP protection. The sulfur and phosphorus additives in API GL-4 oils may corrode and etch gear surfaces, leading to component damage and failure.

API GL-5 oils, on the other hand, are recommended for gearboxes that require extreme pressure and EP protection. The sulfur and phosphorus additives in API GL-5 oils protect gear surfaces from wear, pitting, and scoring.

Lead Additives

In terms of lead additives, GL4 oils are allowed a maximum of .000015% lead. GL5 oils, on the other hand, are allowed a maximum of .00005%. So, if you’re looking for an oil with the least amount of lead possible, GL5 is the way to go.

But that’s not the only difference. GL4 oils also contain EP additives, which help protect gear teeth from wear and tear. GL5 oils don’t have these additives, so they’re not as effective in preventing wear and tear.

However, GL5 oils are compatible with more types of gear than GL4 oils are. So, if you have a gear set that’s not compatible with GL4 oils, you may want to go with a GL5 oil. Just be sure to check the compatibility charts before making your decision.


GL4 and GL5 gear oils have different viscosities. GL4 gear oil is thinner than GL5 gear oil. This means that GL4 gear oil will flow more easily and be less likely to cause damage to gears. GL5 gear oil is thicker and will provide more protection to gears but may cause damage to them if it is too thick.


GL4 oils are typically compatible with yellow metals, whereas GL5 oils contain sulfur-phosphorus EP (extreme pressure) additives that can be corrosive to brass, bronze, and copper alloys. For this reason, GL5 oils are not typically used in transmissions that contain yellow metals.

Shear Stability

So, what about shear stability? This is where GL5 really shines. Because of the higher level of additives, GL5 has much better shear stability. This means that it can withstand higher temperatures and loads without breaking down.

This is especially important in high-performance applications where there is a lot of friction and heat. It’s also important in heavy-duty applications where the gears are under a lot of stress.

So, if you’re looking for the best gear oil for your application, it really depends on what you’re using it for. If you need the best possible protection against wear and tear, then you should go with GL5. But if you’re looking for the best possible price, then GL4 is the way to go.


Now the final consideration is price. Usually, GL-5 gear oil is going to be more expensive than GL-4 gear oil. This is because it’s a more specialized product and there’s simply less demand for it.

However, the price difference isn’t usually significant, so if you need GL-5 gear oil for your application, it’s not worth skimping on quality just to save a few dollars.

At the end of the day, the most important thing is to use the right gear oil for your application. Whether that’s GL-4 or GL-5, make sure you do your research and use the product that’s going to keep your gears running smoothly for years to come.

Can You Mix GL-4 And GL-5


Q. Is An API GL5 Gear Oil Better Than an API GL4 Gear Oil?

Now that we know the difference between GL4 and GL5 gear oils, let’s answer the question: is an API GL5 gear oil better than an API GL4 gear oil?

The simple answer is no, they’re not necessarily better. It just depends on what you need them for.

If you’re looking for something that’s compatible with copper and brass components, then you’ll want to go with a GL4 gear oil. But if you need something that can withstand high temperatures and has excellent wear protection, then you’ll want to choose a GL5 gear oil.

Q. Can You Mix GL-4 And GL-5?

You might be wondering if it’s okay to mix GL-4 and GL-5 gear oils. After all, they both serve the same purpose, right?

Well, not exactly. GL-4 and GL-5 gear oils both have different purposes. GL-4 is designed for use in manual transmissions and hydraulic systems, while GL-5 is designed for use in differentials, gears, and transfer cases.

If you try to use a GL-4 gear oil in a differential that calls for a GL-5 gear oil, you could end up with some serious problems. The oil might not be able to handle the heat and friction that’s generated in a differential, which could lead to damage.

Q. Is It Possible to Use Gl-5 Gear Oil in a Car That Requires Gl-4?

Yes! you can, but you should not. Because Gl-5 gear oil is designed for use in transmissions and differentials that have Hypoid gears. These are the type of gears that you’ll find in most cars—the ones with teeth that are cut at an angle.

Now, the thing with Gl-5 gear oil is that it contains sulfur and phosphorus, which can actually damage yellow metals like bronze and brass. And since most car transmissions have these types of metals, using Gl-5 gear oil in your car could do some serious damage.

So, while it is technically possible to use Gl-5 gear oil in a car that requires Gl-4, it’s not something that we would recommend. If you’re not sure what type of oil to use in your car, always check the owner’s manual or ask a professional.

Final Thought

There is no doubt that both GL-4 and GL-5 are incredible gear oils. But can you use GL-5 gear oil instead of GL-4? We would not recommend it.

If you use GL-5 oil you will notice results very quickly. Take care of your car if you want to enjoy a hassle-free ride.

Is there anything else we miss out on? If yes; then feel free to comment on us. We will surely try to answer you. Thank you all.

Check: GL-6 Gear Oil


Emon is Lubricants specialist who studied on Petroleum Engineering in UAE. He have more than 10 years experience on different kinds of lubrication including automobile troubleshooting.