What Does GL Mean in Oil?

When you see the letters GL on the oil label, you might wonder what they mean. GL stands for extreme pressure rating, and this rating is important when you’re trying to maintain the performance of your vehicle. It also means that the oil contains a certain amount of additives, which are necessary for certain parts of your car. Luckily, GL oil is a good choice for all of these parts, and it’s a very versatile oil.

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The API GL-4 in oil specification is designed for use in heavy-duty commercial manual transmissions. This oil has a high extreme pressure additive activity, which reduces the risk of metal fatigue and spalling under moderate loads. It is also ideal for lubricating drive axles with spiral bevel gears.

GL-4 gear oil has lower levels of extreme-pressure additives than GL-5 gear oil. These additives are essential for protecting gears during extreme conditions. GL-5 gear oil contains twice as much EP additive as GL-4. These oils are typically recommended for heavy-duty manual transmissions and heavy-duty manual gear applications.

GL-4 lubricant is the most effective lubricant for off-road transmissions. The additives work in conjunction with quality base oils to protect gearboxes from performance-compromising effects. This oil has excellent viscosity-temperature properties at both high and low temperatures, making it a great choice for a variety of applications.

GL-5 is intended for heavy-duty gear sets that experience high sliding forces. Hypoid differentials, which are commonly used in heavy-duty trucks, require a different lubricant than GL-4. These differentials are often used in heavy-duty vehicles, such as Caterpillar scrapers and on-road trucks. Some manual-shift transmissions may also use GL-5 lubricant, though it should be noted that EP additives can be harmful to yellow metals.

API GL-4 gear oil is suitable for a small axial offset, and is the minimum standard for synchronized manual transmissions in Europe. It is also suitable for large axial offset and for differentials. It is best to check for the specific requirements of the oil before using it.


GL-5 gear oil is recommended for high-performance, extreme-service applications. It provides excellent lubrication, wear resistance, and protection against rust. This multipurpose gear oil is suitable for both conventional and high-performance differentials. However, you should consult with the manufacturer before using GL-5.

It should be noted that GL-5 gear oil has higher Extreme Pressure (EP) levels than GL-4. This is because GL-5 contains more EP additives, which prevent microwelds on gear flanks. It also improves cold-weather performance. A higher GL category should be used for gear oil, unless the manufacturer has recommended a different level of EP.

GL-4 gear oil is less aggressive and uses half as much sulfur/phosphorus additives than GL-5. Consequently, it does not damage synchronizers as much. But, it will eventually wear down. On the other hand, GL-5 gear oil has four times as much copper.

API GL-5 is a standard for hypoid gear lubricants in automotive transmissions. It also includes oils for high-speed and high torque axles. It is also approved for use in military applications. Some oils are MIL-L-2105D or MIL-PRF-2105E.


API GL-5 and GL-6 in oil are two types of lubricants that have different properties. These types of oils are suitable for axles and gearboxes of light trucks and passenger cars that are operated under various conditions. API GL-5 and GL-6 in oils are meant for axles and gearboxes with high pinion offset that require protection against gear scoring.

GL-5 oil is ideal for use in manual truck transmissions. Its high EP rating makes it an excellent choice for these transmissions. GL-5 is the replacement for GL-4 oil in many applications. It is also suitable for use in limited-slip differentials and high pinion offset hypoid gears. These oils are also approved for use in military vehicles.

GL number is a vital factor for oil protection in gearboxes. Higher GL numbers contain more EP additives that prevent metal-on-metal contact between gears. Choosing the wrong oil grade can lead to tooth wear and synchroniser rings not biting properly. For this reason, it is vital to choose the right oil.

While API GL-5 is considered the best grade of oil, the GL-6 in oil is considered the worst. It contains up to 10% of anti-scuffing additives. API GL-6 oils are not generally recommended for gearboxes.


The API GL-1 performance classification designates a gear oil that meets the basic needs of most high-performance over-the-road transmissions. It is a versatile lubricant that offers protection against thermal degradation, component wear, and oil seal deterioration. Amalie SMG Lubricant GL-1 meets the requirements of this standard and is recommended for use in high-performance over-the-road transmissions.

GL-1 gear oil is ideal for use in manual transmissions and spiral bevel axles. This oil is suitable for light, moderate, and heavy duty conditions. It is also suitable for older classic vehicles. GL-1 gear oil is non-detergent, which makes it a safe choice for gears and other components.

GL-2 is an oil similar to GL-1, but with some EP and anti-wear additives. It is a good choice for hypoid axles under moderate conditions. GL-6 is a dated spec, as it was originally designed for high pinion offset gears. Modern GL-5 oils have greater EP strength and are intended for low-to-moderate loads.

The GL number of the gear oil is important to ensure optimum performance. A higher number means the oil contains more EP additives, which protect the gears from metal-on-metal contact. Using the wrong GL grade can result in teeth wearing out or synchroniser rings not biting.


A high-quality gear oil should be able to withstand high-temperature and high-speed operations. GL-2 in oil is a very good choice for many applications. The castor oil-based formula is also very compatible with copper alloys. Moreover, it meets the original equipment manufacturer specifications.

GL2 is regulated by a transcription factor called MYB23. Its promoter contains two heptamer/octamer elements, HDG2 and HDG11. The latter two transcription factors bind to DNA. However, they differ in amino acid sequence. The two genes have similar functions, and both are involved in regulating the cellular fate of shoot epidermal cells.

In the study, researchers found that two genes, WRI1 and GLABRA2, were critical in regulating the oil content of leaves. A GL2-overexpressing mutant had 8% more oil, but failed to affect the size of the seeds. In addition, GL2 was found to block the formation of trichomes, a structure that is important for seed coat mucilage.

Interestingly, both MYB23 and CESA5 promoters were found to contain the GL2 transcription factor. The presence of MYB23 in seedlings increased the oil content in the seeds, but GL2 itself was not upregulated. Consequently, the MBW complex could not assemble normally.

GL-2 in oil is similar to GL-1, but contains mild EP and anti-wear additives. It is used when GL-1 is not adequate. It is also used in hypoid axles.


Royal Gear Oil GL-3 is an excellent moderate duty gear lubricant for light equipment. It is formulated using the best solvent-refined base oils and extensively proven EP additives. It provides excellent protection against rust, corrosion, foaming, and gear scuffing. It is a great choice for moderate-speed gearing and has excellent anti-scuffing properties.

GL-3 is the most common oil for manual transmissions with moderate or light loads. It has a low EP performance and is not intended for very severe loads. It is recommended for low-speed manual transmissions and spiral bevel axles under light/moderate loads. It has less extreme-pressure (EP) performance than GL-4 oil, and is used to superseed GL-1 oils.

GL-4 is an upgrade of GL-3 and supersedes many applications of GL-3. GL-5 is made for specific applications, and does not work as well in hypoid axles. It is no longer recommended for high-pinion offset gears, such as those in scooters. GL-4 has become increasingly difficult to source, but fully synthetic GL-5 is the best choice.

GL-5 is a gear oil rated for hypoid gears and axles. It is also recommended for non-synchronized manual transmissions, such as those found in buses and heavy-duty trucks. This oil protects against thermal degradation, wear and component deterioration.