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API GL-04 vs. API GL-05: What's the Difference?

Edited by Aimie Carlson || By Janet White || Published on April 13, 2024
API GL-4 is designed for gearboxes with moderate loads, while API GL-5 is formulated for high-load, high-speed applications, offering enhanced protection and performance.

Key Differences

API GL-4 and API GL-5 are classifications of gear lubricants as defined by the American Petroleum Institute (API), differing primarily in their intended use and the level of extreme pressure (EP) protection they offer. API GL-5 lubricants, on the other hand, are formulated for use in automotive differentials and transmissions subjected to higher temperatures and more extreme pressures. They include a higher concentration of EP additives than GL-4 lubricants, providing superior protection against wear and scoring.
The difference in additive composition means that API GL-4 lubricants are often used in applications where gear protection under relatively light loads is essential without the potentially corrosive effects of the higher sulfur content found in GL-5 lubricants. Conversely, API GL-5 lubricants' enhanced thermal stability and resistance to breakdown under high shear conditions make them the preferred choice for high-performance applications. However, due to their aggressive additive package, GL-5 lubricants can potentially damage yellow metal components (like brass and bronze) found in some gearboxes and differentials, unless specifically stated otherwise by the manufacturer.
Both API GL-4 and GL-5 serve to protect gears and bearings from wear and tear, the choice between them depends on the specific requirements of the vehicle's drivetrain components, as outlined by the manufacturer. Using a GL-5 lubricant in a system designed for GL-4 could lead to component damage due to the incompatibility of additives with certain materials.

Comparison Chart

Load Capacity

Designed for moderate loads.
Formulated for high loads and high-speed conditions.

EP Additives

Lower concentration of extreme pressure additives.
Higher concentration of extreme pressure additives.


Suitable for certain manual transmissions and transaxles.
Recommended for automotive differentials and transmissions under severe conditions.

Potential Corrosivity

Less aggressive towards yellow metals.
More aggressive, can damage yellow metals unless specified as safe.

Thermal Stability

Good for moderate temperatures.
Enhanced thermal stability for higher temperatures.

API GL-04 and API GL-05 Definitions


Offers protection under light to moderate loads and speeds.
API GL-4 gear oil is perfect for vehicles that aren't driven aggressively.


May be harmful to yellow metals unless specifically stated as compatible.
Before switching to API GL-5, I confirmed it wouldn't corrode the bronze parts in my transmission.


Contains additives to prevent wear without damaging softer metals.
API GL-4 is formulated to protect gears without harming the brass synchros.


Recommended for vehicles operating under severe conditions.
Off-road vehicles benefit greatly from the enhanced protection of API GL-5.


Suitable for many manual transmissions and front-wheel drive transaxles.
The mechanic recommended API GL-4 for my manual transmission fluid change.


Provides superior protection against wear and scoring.
API GL-5 ensures my differential is protected under extreme conditions.


Less corrosive to yellow metals than higher grade lubricants.
I chose API GL-4 to ensure the longevity of my gearbox's components.


Contains a higher concentration of extreme pressure additives.
The high EP additive content in API GL-5 lubricants guards against gear failure.


API GL-4 lubricants are intended for moderate load conditions.
For my vintage car's gearbox, I only use API GL-4 lubricant.


API GL-5 lubricants are designed for high-load, high-speed applications.
For my high-performance vehicle, API GL-5 gear oil is a must.


What is API GL-4?

API GL-4 is a classification for gear lubricants that specifies the performance requirements for manual transmissions and other gearboxes.

What are the main characteristics of API GL-4 lubricants?

They provide moderate levels of protection against gear wear and pitting, suitable for gear sets operating under moderate conditions.

How does API GL-4 differ from API GL-5?

API GL-4 is designed for lower stress conditions and may not contain the additives necessary for the high-pressure conditions that API GL-5 lubricants can handle.

What types of vehicles use API GL-4?

Typically used in cars, light trucks, and other vehicles with manual transmissions.

Are API GL-4 lubricants suitable for synchromesh transmissions?

Yes, they are often recommended for synchromesh transmissions due to their balanced frictional properties.

Can I use API GL-4 in an application requiring API GL-5?

Generally, no. GL-5 has higher pressure handling capabilities, and using GL-4 could lead to inadequate protection.

What distinguishes API GL-5 lubricants from API GL-4?

GL-5 lubricants have higher concentrations of EP (Extreme Pressure) additives to withstand the demands of higher torque and shock loads.

Can API GL-4 lubricants be used in hypoid gears?

Yes, but only in situations where the manufacturer specifies GL-4 level protection for low to moderate load conditions.

What is the viscosity range for API GL-4 oils?

They can range widely in viscosity to suit different transmission designs and operating temperatures.

How does temperature affect API GL-4 lubricants?

Like all gear oils, their viscosity and performance can vary with temperature; formulations are designed to maintain optimal performance across a specified temperature range.

Are there any specific additives in API GL-4 lubricants?

Yes, they contain additives to prevent oxidation, wear, and corrosion but at lower concentrations compared to GL-5 lubricants.

Can API GL-5 lubricants be used in manual transmissions?

Not recommended if the manufacturer specifies GL-4, as the high additive content may interfere with synchronizer materials causing shifting problems.

What additives are found in API GL-5 lubricants?

Contains high levels of EP additives, as well as agents for protection against rust, oxidation, and foam.

What is API GL-5?

API GL-5 is a gear lubricant classification designed for high-load, high-speed applications, offering enhanced protection against wear and pitting.

Where is API GL-5 commonly used?

Primarily in automotive differentials and industrial gearboxes where high stress and shock loading occur.

Are API GL-5 lubricants backward compatible with GL-4 applications?

Not typically, due to their higher additive levels which can be incompatible with gears and seals designed for GL-4.

What are the viscosity requirements for API GL-5 oils?

Similar to GL-4, they vary widely to accommodate different operating conditions and gear designs.

How do API GL-5 lubricants perform in low temperatures?

They are formulated to ensure adequate flow and protection in low temperatures, though specific performance can vary by product.

Is there a significant cost difference between GL-4 and GL-5?

The cost can vary based on the formulation and specific performance additives used, with GL-5 potentially being more expensive due to its higher additive concentration.

Can API GL-5 oils be used in hypoid gears?

Yes, they are especially recommended for hypoid gears or when gear manufacturers require GL-5 level protection.
About Author
Written by
Janet White
Janet White has been an esteemed writer and blogger for Difference Wiki. Holding a Master's degree in Science and Medical Journalism from the prestigious Boston University, she has consistently demonstrated her expertise and passion for her field. When she's not immersed in her work, Janet relishes her time exercising, delving into a good book, and cherishing moments with friends and family.
Edited by
Aimie Carlson
Aimie Carlson, holding a master's degree in English literature, is a fervent English language enthusiast. She lends her writing talents to Difference Wiki, a prominent website that specializes in comparisons, offering readers insightful analyses that both captivate and inform.

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