Can I Use GL5 Instead Of GL4?


There are quite a few oils available for use in gears, and API (American Petroleum Institute) has classified them into specific categories such as MT-1 etcetera, GL5, and GL4. Usually, GL4 will be the type most used as a lubricant.

Do many people wonder if “Can I use GL5 instead of GL4?” Indeed the following answer will be the information you need!

Can I Use GL5 Instead Of GL4?

The answer is that it is possible to use GL5 oil alternatively of GL4, but this is not appreciated or recommended. Understanding and evaluating this problem can rely on the API GL rankings.

Overall, GL5 is standing higher than that, but why is it not recommended to replace the position of GL4. Find out below! 

Product  Features
“Red Line” 75W140 – GL5 
  • Creates smoothness to help lower running heat.
  • Provides friction modifiers.
  • Support lubrication under severe conditions. 
“Sta-Lube” API – GL4 
  • It contains additives to help prevent corrosion.
  • Contains oil to help avoid wearing gear.
  • High reliability.

Reasons And Analysis 

As we all know, changing the GL5 oil for the GL4 is not recommended. Follow the reasons right below to learn more about this issue!

Associated additives contain phosphorus and sulfur

The one with the greater EP protection is the one with the greater GL rating, and this problem also requires the involvement of more additives. In general, EP additives are related to phosphorus and sulfur compounds.

If you are a person with an understanding of chemistry, you won’t be very pleased to hear these two names. The nature of these two mixtures will often stick to the metal cover and thereby create a polar attraction with another metal. 

Attack on metal coverings

EP additives are added through the polar attraction to wet the metal. Next, generate heat, and additives will attack other metals. A powerful attack will affect and wear out the synchronizers.

Which Standard Assurance Has Fewer Additives?

In general, GL4 contains only half of the additives that GL5 has. Specifically, this means that there will be less protection EP than that but will reduce most of the damage to synchronizers.

If you choose GL5, this is a trade-off for gear protection, but synchronizers will suffer a lot. We can estimate that the synchronizer will wear so much and to the point of not contacting the side, other parts, and even the gears. 

What Is The Distinction Between GL5 And GL4?

Although these two oils are similar, there are quite noticeable differences. The following information will help you find out the details:

“EP” Additives

The most significant difference between these two substances lies in the EP additives. In particular, the additives associated with phosphorus and sulfur compounds will have a high degree of corrosion. Metals will be attacked by these compounds when in the process of generating a lot of heat.

In general, to ensure the best, you should choose the type with fewer additives. While the GL4 is excellent for you, the GL5 has an unbelievable amount of additives.

“EP” Protection

The GL level rating would be the way to determine the level of EP protection. Specifically, the ranking details will start with GL1 up to GL6 and MT1. For example, a GL level of 5 provides a higher level of protection under extreme conditions such as loads, torques, and speed.

Overall the GL5 has more protection than the GL4, and GL4 will also handle torques and speed. However, in the case of high pressure and heat, the GL5 has an advantage. Meanwhile, the GL4 has excellent protection for the gears. 


Viscosity plays an important role in the process of making the engine work. In GL5 oil, the viscosity is high because it contains many additives. GL4 contains few additive compounds, which should reduce the viscosity of the additive.

Lead Additives

“Lead” will be utilized and added in additives to help decrease gear wear. Although this is environmentally-unfriendly material, combining it with phosphorus and sulfur will help you reduce the harm. Components in GL5 contain more lead than GL4.

Can I Combine GL5 And GL4?

You can mix GL5 in GL4 oils and use this mixture for transmissions. In addition, you can also integrate GL5 with MT1 to use for gearboxes.

Most of the essential recommendations advise against using GL5 oil in your engine. Even though you have mixed it with another oil like GL4, it still finds the potential to damage other copper components inside the transmission.

In general, to ensure the best for the gearbox, you still should not use the GL5, even if it is a mixture. In some emergencies, you can use it, such as not immediately supplying GL4.

Which Oil Is More Beneficial?

GL4 will undoubtedly be the more appreciated name for gear guarantee. You can evaluate and choose the most suitable compound from the information mentioned above.

If you use the GL5 in extreme conditions, you are making things worse. The types of phosphorus/sulfur compounds inside the additives will directly affect the covering of the alloy/metal.

GL4 is an excellent choice with protection standards to avoid this dangerous corrosion. In general, GL4 is consistently rated better in all aspects than GL5.

A Few Tips For You

A few tips will help if you think about using GL5 as a replacement for GL4. The fact that manufacturers have created oils and classified them differently is all for a purpose.

You will easily confuse them to be the same, but the ingredients inside them are significantly different. In particular, when choosing an oil, you need to pay attention to the characteristics and composition of each oil for each type of engine. This issue will be helpful to you in these circumstances.


If you were wondering, “Can I use GL5 instead of GL4?, you have found a great answer based on the information provided above. Overall, each oil class has different properties, and it is essential to understand their function before using or intending to interchange them.

Hopefully, this helpful information will help you make the best choices for your engine!

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