Engine oil specifications are regulated primarily by two major organisations:

• The American Petroleum Institute (API) – responsible for setting engine oil standards in the United States and associated markets.
• The Association des Constructeurs Européens d’Automobiles (ACEA) – which defines engine oil standards for the European market.

In addition, many Original Equipment Manufacturers (OEMs) such as BMW and Mercedes-Benz maintain proprietary engine oil specifications. While many of these align with API and ACEA standards, we recommend consulting the Vertex online Lubrication Guide or reaching out to our Technical Team to ensure you select the correct engine oil for your vehicle.

Below is a guide to API and ACEA Engine Oil Sequences.

American Petroleum Institute (API) Oil Categories

Current and past API Service Categories are shown in easy-to-read charts. Vehicle owners should first check their owner’s manual. Some oils meet multiple performance levels. For gasoline engines, the latest category includes the properties of previous ones. For example, if an API SN oil is recommended, an API SP oil will fully protect the engine. In diesel engines, the newest category generally—but not always—includes previous ones.

API FA-4 oils, labelled with the FA-4 Donut, are formulated for specific XW-30 diesel engines meeting 2017 GHG emission standards. These oils are not interchangeable with API CK-4, CJ-4, or earlier categories; refer to the engine manufacturer’s recommendations to confirm compatibility.

ILSAC Standards for Passenger Car Engine Oils

Current ILSAC standards are listed here, but vehicle owners should check their owner’s manual first. Some oils meet multiple performance levels. The latest ILSAC standard includes the properties of previous ones, allowing it to service older engines that recommended earlier oils.

Gasoline Engines “S” Specifications

Current API Service Categories are listed here; however, vehicle owners should consult their owner’s manual first. Some oils meet multiple performance levels. The latest API Service Category includes the properties of previous ones, making it suitable for servicing older engines that recommended earlier oils.

Diesel Engines “C” Specifications

(Follow your vehicle manufacturer’s recommendations on oil performance levels)

Diesel Engines “F” Specifications

(Follow your vehicle manufacturer’s recommendations on oil performance levels)

Association des Constructeurs Européens d’Automobiles (ACEA) Oil Sequences

A/B Specifications: Gasoline and Diesel Engine Oils – “High SAPS” 

A3/B3 Category withdrawn with these Oil Sequences. Stable, stay-in-grade engine oil intended for use in passenger car and light-duty gasoline & diesel engines and/or for extended oil drain intervals where specified by the engine manufacturer.

A3/B4 Stable, stay-in-grade engine oil intended for use at extended oil drain intervals in passenger car and light-duty gasoline & DI diesel engines, but also suitable for applications described under A3/B3.

A5/B5 Stable, stay-in-grade engine oil intended for use at extended oil drain intervals in passenger car and light-duty gasoline & DI diesel engines designed for low viscosity engine oils with HTHS viscosity of 2.9 to 3.5 mPa.s. These engine oils are unsuitable for use in certain engines – consult vehicle-OEM’s owner’s manual/handbook in case of doubt.

A7/B7 Stable, stay-in-grade engine oil intended for use at extended oil drain intervals in passenger car and light-duty gasoline & DI diesel engines designed for low viscosity engine oils with HTHS viscosity of 2.9 to 3.5 mPa.s. Relative to A5/B5 these engine oils provide also low speed pre-ignition- and wear protection for turbocharged gasoline DI engines as well as turbocharger compressor deposit (TCCD) protection for modern DI diesel engines. These engine oils are unsuitable for use in certain engines – consult vehicle-OEM’s owner’s manual/handbook in case of doubt.

C Specifications: Catalyst & GPF/DPF compatible Engine Oils for Gasoline & Diesel Engines – “Low SAPS”

Note: These Oils will increase the DPF/GPF and TWC life and maintain the Vehicle’s Fuel economy.

Warning: Some of these Categories may be unsuitable for use in certain Engine Types – consult the vehicle OEM’s owner’s manual/handbook in case of doubt.

C1: Category Obsolete.

C2: Stable, stay-in-grade engine oil with mid-SAPS Level, for aftertreatment system compatibility. Intended for use at extended oil drain intervals in passenger car and light-duty gasoline & DI diesel engines designed for low viscosity engine oils with a minimum HTHS Viscosity of 2.9 mPa s.

C3: Stable, stay-in-grade engine oil with mid-SAPS Level, for aftertreatment system compatibility. Intended for use at extended oil drain intervals in passenger car and light-duty gasoline & DI diesel engines designed for engine oils with HTHS viscosity of minimum 3.5 mPa.s.

C4: Stable, stay-in-grade engine oil with low-SAPS Level, for aftertreatment system compatibility. Intended for use at extended oil drain intervals in passenger car and light-duty gasoline & DI diesel engines designed for engine oils with HTHS viscosity of minimum 3.5 mPa.s.

C5: Stable, stay-in-grade engine oil for improved fuel economy, with mid-SAPS Level, for aftertreatment system compatibility. Intended for use at extended oil drain intervals in passenger car and light-duty gasoline & DI diesel engines designed and OEM-approved for engine oils with HTHS viscosity of minimum 2.6 mPa.s.

C6: Stable, stay-in-grade engine oil for improved fuel economy, with mid-SAPS Level, for aftertreatment system compatibility. Intended for use at extended oil drain intervals in passenger car and light-duty gasoline & DI diesel engines designed and OEM-approved for engine oils with HTHS viscosity of minimum 2.6 mPa.s. Relative to C5 these engine oils provide also low speed pre-ignition- and wear protection for turbocharged gasoline DI engines as well as turbocharger compressor deposit (TCCD) protection for modern DI diesel engines.

Glossary:

SAPS: Sulphated Ash, Phosphorus, Sulphur

HTHS: High Temperature High Shear Viscosity

DI:      Direct Injection

DPF:   Diesel Particle Filter

GPF:   Gasoline Particle Filter

TWC: Three-Way Catalyst

E Specifications: Heavy Duty Diesel Engine Oils 

E4: Stable, stay-in-grade oil providing excellent control of piston cleanliness, wear, soot handling and lubricant stability. It is recommended for highly rated diesel engines meeting Euro I, Euro II, Euro III, Euro IV and Euro V emission requirements and running under very severe conditions, e.g. significantly extended oil drain intervals according to the manufacturer’s recommendations. It is suitable for engines without particulate filters, and for some EGR engines and some engines fitted with SCR NOx reduction systems. However, recommendations may differ between engine manufacturers so driver manuals and/or dealers shall be consulted if in doubt.

E6: Stable, stay-in-grade oil providing excellent control of piston cleanliness, wear, soot handling and lubricant stability. It is recommended for highly rated diesel engines meeting Euro I, Euro II, Euro III, Euro IV, Euro V and Euro VI emission requirements and running under very severe conditions, e.g. significantly extended oil drain intervals according to the manufacturer’s recommendations. It is suitable for EGR engines, with or without particulate filters, and for engines fitted with SCR NOx reduction systems. E6 quality is strongly recommended for engines fitted with particulate filters and is designed for use in combination with low sulphur diesel fuel. However, recommendations may differ between engine manufacturers so driver manuals and/or dealers shall be consulted if in doubt.

E7: Stable, stay-in-grade oil providing effective control with respect to piston cleanliness and bore polishing. It further provides excellent wear control, soot handling and lubricant stability. It is recommended for highly rated diesel engines meeting Euro I, Euro II, Euro III, Euro IV and Euro V emission requirements and running under severe conditions, e.g. extended oil drain intervals according to the manufacturer’s recommendations. It is suitable for engines without particulate filters, and for most EGR engines and most engines fitted with SCR NOx reduction systems. However, recommendations may differ between engine manufacturers so driver manuals and/or dealers shall be consulted if in doubt.

E8: Improves upon E6 by enhancing oxidation resistance, aeration control, and piston cleanliness. Backward compatibility means E8 oils can replace E6 oils in engines that previously required ACEA E6. E8 Focuses on modern emissions standards with Low SAPS formulation, making it ideal for engines with advanced after-treatment systems. E8 includes the Volvo T-13 oxidation test, a rigorous standard that evaluates an oil’s resistance to oxidation, which is critical for extended drain intervals and high-temperature applications. The E8 specification uses the OM471 test (a replacement for the OM501LA test used in E6) to ensure high levels of piston cleanliness and wear protection, particularly important for engines equipped with after-treatment devices. E8 is tested to conform to the Caterpillar Oil Aeration Test (COAT) to measure the oil’s ability to resist aeration, which is crucial for maintaining stable oil pressure and preventing power loss.

E9: Stable, stay-in-grade oil providing effective control with respect to piston cleanliness and bore polishing. It further provides excellent wear control, soot handling and lubricant stability. It is recommended for highly rated diesel engines meeting Euro I, Euro II, Euro III, Euro IV, Euro V and Euro VI emission requirements and running under severe conditions, e.g. extended oil drain intervals according to the manufacturer’s recommendations. It is suitable for engines with or without particulate filters, and for most EGR engines and for most engines fitted with SCR NOx reduction systems. E9 is strongly recommended for engines fitted with particulate filters and is designed for use in combination with low Sulphur diesel fuel. However, recommendations may differ between engine manufacturers so driver manuals and/or dealers should be consulted if in doubt.

E11: Introduced in 2022 as part of an update to ACEA’s heavy-duty diesel engine oil categories. E11 replaces the older E9 category, targeting improved performance in oxidation stability, aeration resistance, and piston cleanliness, using tests that align with API CK-4 standards. Oils meeting E11 are formulated for high-load, extended-drain applications and are suited for Euro VI diesel engines while also being backward-compatible with older engine standards (Euro V and below)​. The ACEA E11 standard requires a low ash content (less than 1%) to protect emissions control systems, such as diesel particulate filters. It also includes rigorous tests for aeration, which ensures the oil maintains pressure and performance in high-demand environments, helping prevent issues like loss of power due to foaming. Additionally, E11 addresses bore polishing through stringent piston cleanliness and wear-resistance benchmarks, making it suitable for heavy-duty applications across diverse environmental conditions​.

Brake Fluids

Brake fluid acts as a non-compressible hydraulic fluid to transfer power to the braking system.

This article will focus on the correct storage and handling of brake fluids.

Brake fluids are hydroscopic, meaning that the fluid absorbs atmospheric moisture over time. The hydroscopic properties of brake fluids have both advantages and disadvantages as listed below:

Advantages of Hygroscopic Property – Moisture Absorption

Uniform Distribution

The hygroscopic nature helps in evenly distributing the absorbed moisture throughout the brake fluid. This prevents the formation of water pockets within the braking system, which can lead to localised boiling and vapor lock.

Corrosion Inhibition

By absorbing moisture, the brake fluid helps to reduce the likelihood of free water causing rust and corrosion in the brake system.

Disadvantages of Hygroscopic Property – Moisture Absorption

Decreased Boiling Point

Over time, as the fluid absorbs moisture, its boiling point decreases. This can lead to a higher risk of brake fluid boiling under heavy braking conditions, causing brake fade or vapor lock, which compromises braking performance.

Regular Maintenance Requirement

Due to moisture absorption, glycol-based brake fluids need to be changed regularly to maintain optimal performance and safety. The absorbed moisture can degrade the fluid’s effectiveness, necessitating more frequent maintenance.

Brake Fluid Handling and Storage

Due to the hydroscopic nature of brake fluid, it is essential to adhere to correct storage and handling procedures. Due to heat generation during braking, it is important to understand brake fluids boiling point. A brake fluid technical data sheet will list the dry and wet boiling point of brake fluids. The dry boiling point listed is the temperature at which pristine unused brake fluids will boil. The wet boiling point lists the temperature at which the brake fluid will boil after 3.7% absorption of water by volume from the atmosphere. The usual absorption rate to reach 3.7% water absorption is 12-months in a sealed braking system. It must be noted that the 3.7% absorption is only an estimate and that poor handling procedures can accelerate water absorption.

Vertex DBF DOT 4 exhibits a dry boiling point of 230^oC, whilst the wet boiling point has dropped to 155^oC. This represents a decreased boiling point of 75^oC.

Brake Fluid Handling Procedures

It is important to reduce brake fluids from atmospheric exposure. To reduce exposure to water absorption, the correct procedure is to always completely drain braking systems of fluid and refill with pristine product from a sealed container. Due to the nature of bulk supply, this is not always possible, so the following procedures should be adopted when servicing brake systems with fluid drawn from bulk containers:

1. Minimise atmospheric exposure by keeping lids tightly secured on all containers containing brake fluids.
2. If lids need to be removed, they must be securely fastened as soon as possible. Leaving brake fluid exposed is a safety hazard due to degradation of the fluid through water absorption.
3. Do not transfer brake fluids from the original container to a different container. Agitation during the transfer process will substantially increase water absorption and subsequent degradation of the fluid.
4. When servicing braking systems, do not top up the fluid reservoir; a complete drain and subsequent replacement of new fluid is required. If an emergency fluid top up is required, a full system drain should be conducted as soon as practical. The requirement to fully replace brake fluids is not limited to product drawn from bulk supply, but also includes product drawn from sealed containers.
5. The generally accepted life expectancy of brake fluid is 12-months; therefore, all brake fluids need to be replaced after 12-months of use to ensure safe working operation of the fluid.
6. The generally accepted upper limit of water content in brake fluid is around 3.0%. The use of brake fluid water content testers is encouraged. Brake fluid water content testers are inexpensive and can adequately ensure the integrity of brake fluids. Ensure any brake fluid water content testers are compatible with the type of brake fluid in use.
7. If a brake fluid water content tester is unavailable, visual inspection of the fluid can assist in determining the viability of the fluid. Noticeable darkening or colour changes may be an indication of contamination with water or other undesirable contaminates.
8. Store brake fluids in a stable environment. Moving cooled break fluids into a hotter environment will cause condensation and accelerated water absorption. Before using brake fluids, move the container into an area of the same temperature where the fluid will be drawn. Allow time for the temperature to equalise.

Hydraulic Fluids: Anti-Wear, Zinc-Free, Biodegradable, High Viscosity Index and Fire-Resistant Options

Introduction

Hydraulic systems provide power transfer through the compression of fluids. Choosing the right hydraulic fluid is essential for ensuring system efficiency, reducing wear, and extending the life of components. This article explains the key types of hydraulic fluids—anti-wear, zinc-free, high viscosity index, and fire-resistant – helping users understand their benefits and applications.

Anti-Wear Hydraulic Fluids

Anti-wear (AW) hydraulic fluids are the most common type of hydraulic fluids. These fluids are designed to protect metal surfaces from friction and wear, which can lead to system failure over time. Anti-wear fluids contain additives—commonly zinc-based compounds like zinc dialkyldithiophosphate (ZDDP)—that form a protective layer on metal parts, preventing direct contact.

Benefits

• Reduces wear on pumps and valves, extending equipment life.
• Enhances performance in high-pressure systems.
• Provides oxidation stability, reducing sludge and deposit formation.

Applications

• Construction and mining equipment.
• Manufacturing machinery.
• Hydraulic presses and injection moulding machines.

Zinc-Free Hydraulic Fluids

While anti-wear fluids often use zinc-based additives, some systems require zinc-free hydraulic fluids. These fluids use alternative anti-wear chemistry, such as phosphorus- or sulphur-based additives, to protect equipment while eliminating the potential downsides of zinc.

Why Choose Zinc-Free Fluids?

• Environmental and Regulatory Compliance. Some industries require zinc-free fluids due to concerns over water contamination and disposal regulations.
• Compatibility with Yellow Metals. Zinc-based fluids can react with components made from brass, bronze, or copper, leading to corrosion.
• Suitability for Specific Equipment. Certain hydraulic pumps and motors require zinc-free formulations to prevent performance issues.

Common Applications

• Marine and offshore equipment.
• Food processing and pharmaceutical industries.
• Power generation and environmentally sensitive applications.

High Viscosity Index (HVI) Hydraulic Fluids

Viscosity is a measure of a fluid’s resistance to flow, and the viscosity index (VI) indicates how much that viscosity changes with temperature. High viscosity index (HVI) hydraulic fluids are formulated to maintain stable viscosity across a wide temperature range, making them ideal for applications subject to extreme temperature fluctuations.

Advantages of HVI Fluids

• Consistent Performance in All Climates. They resist thinning in high temperatures and thickening in cold conditions.
• Improved Efficiency. Stable viscosity reduces energy loss and improves system response time.
• Longer Fluid Life. Reduced oxidation and thermal breakdown extend service intervals.

Ideal Uses

• Outdoor equipment operating in extreme temperatures.
• Aviation and aerospace hydraulics.
• Forestry and agricultural machinery.

Biodegradable Hydraulic Fluids

As industries seek environmentally friendly solutions, biodegradable hydraulic fluids have gained popularity. These fluids are designed to break down naturally, reducing environmental impact in case of leaks or spills.

Benefits of Biodegradable Fluids

• Eco-Friendly. Made from renewable sources like vegetable oils or synthetic esters, they degrade quickly in the environment.
• Regulatory Compliance. Many industries, such as forestry and marine operations, require biodegradable fluids to meet environmental standards.
• Good Lubrication and Wear Protection. Modern biodegradable fluids offer performance comparable to conventional fluids while being less harmful to ecosystems.

Common Applications

• Forestry and agricultural equipment.
• Marine and offshore operations.
• Construction sites near water sources.

Fire-Resistant Hydraulic Fluids

In environments where fire hazards are a concern, fire-resistant hydraulic fluids are essential for improving safety and reducing the risk of ignition. These fluids are designed to operate under extreme conditions while minimising fire hazards.

Types of Fire-Resistant Fluids

• Water-Glycol Fluids (HFC). Contain a mixture of water and glycol, offering excellent fire resistance but requiring specific system compatibility.
• Phosphate Ester Fluids (HFD-R). Provide high thermal stability and are commonly used in aerospace and power generation applications.
• Synthetic Ester Fluids (HFD-U). Offer a balance of fire resistance and biodegradability, making them suitable for industrial use.

Benefits of Fire-Resistant Fluids

• Enhanced Workplace Safety. Reduces the risk of ignition in high-temperature or high-pressure environments.
• Regulatory Compliance. Many industries require fire-resistant fluids to meet safety standards.
• System Protection. Helps prevent catastrophic failures due to fluid ignition.

Common Applications

• Steel mills and foundries
• Aviation and aerospace systems
• Underground mining and tunnelling equipment

Choosing the Right Hydraulic Fluid

Selecting the right hydraulic fluid depends on the specific needs of your equipment and operating environment. Consider the following:

• Manufacturer Recommendations. Always check OEM guidelines for fluid compatibility.
• Operating Conditions. For high-pressure systems, anti-wear fluids may be necessary. For temperature extremes, HVI fluids provide stability.
• Environmental Considerations. Zinc-free fluids or Biodegradable fluids may be required in sensitive applications.
• Environments where fire hazards are a concern, choose fire-resistant hydraulic fluids.

Conclusion

Understanding the differences between anti-wear, zinc-free, high viscosity index, biodegradable and fire-resistant hydraulic fluids ensure optimal performance and longevity of hydraulic systems. By selecting the right fluid for the job, operators can reduce wear, improve efficiency, and comply with environmental and safety regulations. If in doubt, consult with a Vertex lubricant specialist to determine the best fluid for your application.

Introduction

Gear oils are essential lubricants in various mechanical systems, playing a critical role in reducing friction, dissipating heat, and preventing wear and corrosion. Among the key components of gear oils are extreme pressure (EP) additives, which are designed to enhance the lubricating properties of the oil under high-pressure conditions. In this article, we delve into the mechanics of gear oils, focusing particularly on the function and mechanism of extreme pressure additives. We will also discuss the differences in Gear Oil GL ratings, Gear Oil Viscosities and the importance of understanding correct Gear Oil selection.

Fundamentals of Gear Oils

Gear oils are formulated to provide lubrication in systems with sliding or rolling contacts, such as gearboxes, transmissions, and differentials. These oils must withstand high loads, speeds, and temperatures while maintaining their lubricating properties over extended periods.

Key Characteristics of Gear Oils

1. Viscosity: Gear oils are available in various viscosity grades, which determine their flow properties at different temperatures. Proper viscosity selection is crucial to ensure adequate lubrication under both low and high operating conditions.
2. Film Strength: The ability of the oil to form a durable lubricating film between moving surfaces is critical in preventing metal-to-metal contact and subsequent wear. Vertex’s range of Synthetic Gear Lubricants provide superior Film Strength over conventional Mineral Based Gear Lubricants.
3. Oxidation Stability: Gear oils must resist oxidation, which can lead to the formation of sludge, varnish, and corrosive by-products, degrading lubricant performance and equipment longevity. Vertex’s range of Synthetic Gear Lubricants provide superior Oxidation Stability over conventional Mineral Based Gear Lubricants.
4. Corrosion Protection: Effective gear oils contain additives to protect metal surfaces from corrosion, particularly in environments exposed to moisture and contaminants.

Role of Extreme Pressure Additives

Extreme pressure additives are incorporated into gear oils to provide enhanced lubrication under conditions of high pressure, shock loading, and boundary lubrication. These conditions occur in gear teeth contact areas, during engine power transfer via gearboxes, differentials, and final drives. Gear teeth meshing during power transfer undergoes significant forces and high temperatures which can lead to metal-to-metal contact, scuffing, and wear. Lubricants are squeezed out during high load and gear teeth contact and offer limited protection against wear. The use of Extreme Pressure Additives provides protection and longevity of the equipment through the formation of Tribofilms which create “Sacrificial Wear Layers” in the absence of adequate boundary lubrication during oil squeeze out.

Mechanism of Extreme Pressure Additives:

1. Formation of Tribofilms: Extreme pressure additives contain active ingredients such as sulphur-phosphorus compounds, chlorinated compounds, or solid lubricants like molybdenum disulfide. When subjected to high pressures and temperatures, these additives react with metal surfaces to form protective tribofilms. Tribofilms act as sacrificial layers, reducing friction and wear by providing a barrier between contacting surfaces.
2. Chemical Reactions: Extreme pressure additives chemically react with the metal surfaces, forming chemisorbed layers that offer increased resistance to welding and seizure under extreme loading conditions.
3. Boundary Lubrication Enhancement: Under boundary lubrication conditions, where the oil film thickness is insufficient to fully separate moving surfaces, extreme pressure additives ensure lubrication by forming protective layers that minimise metal-to-metal contact and friction.

Performance Considerations:

1. Compatibility: Extreme pressure additives must be compatible with other additives present in the gear oil formulation to avoid adverse interactions that could compromise performance or lead to equipment damage.
2. Temperature Stability: The effectiveness of extreme pressure additives can be influenced by temperature variations. Proper formulation and selection of additives ensure stability and performance across a range of operating temperatures – Vertex Synthetic Gear Lubricants provide better temperature stability than conventional mineral based products.
3. Environmental Impact: Some extreme pressure additives, particularly those containing chlorine, may raise environmental concerns due to their potential toxicity and persistence. Manufacturers must balance performance requirements with environmental considerations when formulating gear oils.

Extreme pressure additives play a crucial role in enhancing the performance and longevity of gear oils in demanding industrial and automotive applications. By forming protective tribofilms and chemisorbed layers, these additives minimise friction, wear, and scuffing under extreme operating conditions, ensuring smooth and reliable operation of mechanical systems. However, proper formulation, compatibility, and environmental considerations are essential to maximise the benefits of extreme pressure additives while minimising potential drawbacks.

Understanding Gear Lubricant (GL) Ratings:

Gear lubricants are classified according to their performance characteristics and application suitability using the Gear Lubricant (GL) rating system. This system, established by the American Gear Manufacturers Association (AGMA), provides a standardised method for categorising gear oils based on their load-carrying capacity, viscosity, and other essential properties.

1. GL Rating Scale: The GL rating scale consists of different classifications, denoted by alphanumeric codes such as GL-1, GL-4, GL-5, etc. Each classification indicates specific performance attributes and application suitability.
2. Key Factors Considered:
   • Load-Carrying Capacity: The ability of the gear oil to withstand high loads without failure is a crucial consideration. Higher GL ratings typically indicate greater load-carrying capacity, making them suitable for heavy-duty applications, however, higher gear oil ratings can be detrimental in components containing metals such as brass or bronze – more on this later.
   • Extreme Pressure (EP) Performance: GL ratings often correlate with the gear oil’s ability to provide effective lubrication under extreme pressure conditions. Gear oils with higher GL ratings usually incorporate enhanced EP additives to improve performance under high-pressure and shock-loading conditions.
   • Viscosity and Temperature Stability: The viscosity grade and temperature stability of gear oils are essential factors in determining their performance across a range of operating conditions. GL ratings may also reflect the viscosity requirements for specific applications, ensuring adequate lubrication under varying temperature and load conditions.
3. Common GL Ratings:
   • GL-1: These gear oils are typically mineral-based and offer basic lubrication properties. They are suitable for manual transmissions and light-duty gearboxes with low-speed, low-load applications. However, some Heavy-Duty Transmissions (such as Eaton Fuller and Roadranger Transmissions) contain metallurgical and design properties requiring a GL-1 rated Lubricant; for example, Vertex Transgear RR 50 is rated as a GL-1 Gear Lubricant.
   • GL-4: Gear oils with GL-4 rating offer improved EP performance compared to GL-1 oils. They are suitable for moderate-duty automotive transmissions, hypoid gears, and spiral bevel gears operating under moderate loads and speeds. For example, Vertex Transgear 4 80W-90 is a GL-4 rated Gear Lubricant.
   • GL-5: GL-5 rated gear oils provide high-load-carrying capacity and are formulated with robust EP additives to withstand extreme pressure conditions. They are suitable for heavy-duty automotive differentials, industrial gearboxes, and other applications subjected to high loads and shock loading. For example, Vertex Transgear 5 80W-90 is a GL-5 rated Gear Lubricant.
   • GL-6: This rating is less commonly used but indicates gear oils designed for severe-duty applications with exceptionally high loads and extreme pressure conditions. GL-6 has been obsoleted, and Vertex does not carry a GL-6 Gear Lubricant.

4. Compatibility and Interchangeability:

• While GL ratings provide a useful guideline for selecting gear lubricants, it is essential to ensure compatibility and interchangeability with equipment manufacturer recommendations. Mixing gear oils with different GL ratings or formulations may lead to performance issues, including reduced lubrication effectiveness, increased wear, and equipment damage.

In summary, the GL rating system serves as a valuable tool for selecting gear lubricants based on their performance characteristics and application requirements. By understanding the implications of different GL ratings and matching them to specific operating conditions, equipment operators can ensure optimal lubrication performance, longevity, and reliability of their mechanical systems, however, it must be noted that higher GL ratings do not indicate that lower GL ratings have been superseded, or that higher GL ratings are the correct choice for all applications. In the next section, we shall explore the use of high GL rated Gear Lubricants in Brass and Bronze Gears

Challenges of Using Higher GL Ratings with Brass or Bronze Gears:

While higher GL-rated gear oils offer superior load-carrying capacity and extreme pressure performance, they may not always be compatible with certain gear materials, such as brass or bronze. Brass and bronze are commonly used in gears due to their excellent machinability, wear resistance, and low friction properties. However, these materials can be sensitive to certain additives found in gear oils, particularly those used in formulations with higher GL ratings. Here are some challenges associated with using higher GL-rated gear oils with brass or bronze gears:

1. Corrosion and Metal Attack: Many extreme pressure additives, such as sulfur-phosphorus compounds and chlorinated compounds, can react with copper-based alloys like brass and bronze, leading to corrosion and metal attack. The reactive nature of these additives may accelerate wear and degradation of gear surfaces, compromising gear integrity and performance over time.
2. Yellow Metal Embrittlement: Brass and bronze gears are susceptible to a phenomenon known as “yellow metal embrittlement” when exposed to certain additives present in high GL-rated gear oils. This process involves the diffusion of sulphur from the oil into the metal surface, resulting in the formation of brittle intermetallic compounds. As a result, the gears become more prone to fracture and failure under load, posing a significant safety risk in critical applications.
3. Surface Damage and Pitting: Incompatibility between high GL-rated gear oils and brass/bronze gears can lead to surface damage and pitting due to increased friction and wear. The formation of abrasive compounds or deposits on gear surfaces may exacerbate wear rates, causing premature gear failure and reduced operational reliability.
4. Reduced Gear Life and Efficiency: The use of incompatible gear oils with higher GL ratings can shorten the service life of brass or bronze gears and decrease overall system efficiency. Increased wear, corrosion, and surface damage can lead to higher maintenance costs, downtime, and potential gear replacement, impacting the productivity and profitability of equipment operations. Figure 1 below illustrates erosive gear damage due to incorrect use of a GL-5 Gear Lubricant.

Figure 1. Brass gear damage due to GL-5 extreme pressure additive erosion.

Recommendations for Brass/Bronze Gear Applications:

1. Select Appropriate Gear Oil Formulation: When using brass or bronze gears, it is essential to choose gear oils specifically formulated for compatibility with yellow metals. These oils typically have lower levels of sulphur, phosphorus, and other additives known to cause corrosion or embrittlement in copper-based alloys.
2. Consult Equipment Manufacturer Recommendations: Follow the gear oil recommendations provided by the equipment manufacturer to ensure compatibility and optimal performance. Manufacturers may specify certain gear oil formulations or GL ratings that are suitable for use with brass or bronze gears, taking into account the specific operating conditions and material compatibility requirements.
3. Monitor Gear Condition and Performance: Regular inspection and monitoring of gear condition and performance can help identify early signs of wear, corrosion, or other issues related to lubricant compatibility. Implementing proactive maintenance practices, such as oil analysis and gear inspections, can extend gear life and minimise the risk of unexpected failures.

In conclusion, while higher GL-rated gear oils offer superior performance in terms of load-carrying capacity and extreme pressure protection, they may pose compatibility challenges when used with brass or bronze gears. By selecting appropriate gear oil formulations, following manufacturer recommendations, and monitoring gear condition, operators can mitigate the risks associated with lubricant-induced damage and ensure the reliable operation of brass or bronze gear systems.

Other Considerations – Carbonitrided Gears

Carbon-coated gears, also known as carbonitrided gears, are typically steel or brass gears that have undergone a surface treatment process to improve wear resistance and reduce friction. This treatment involves introducing carbon and nitrogen into the surface layer of the gear through a diffusion process, forming a hard, wear-resistant carbonitride layer.

When it comes to gear lubrication, the choice of gear oil is critical to ensure optimal performance and longevity of carbon-coated gears. While GL-5 gear oils are formulated to provide excellent extreme pressure (EP) protection and load-carrying capacity, they may not be suitable for use with carbon-coated gears due to the potential for damage.

1. Chemical Compatibility: GL-5 gear oils contain EP additives, such as sulphur-phosphorus compounds and chlorinated compounds, which can react adversely with certain surface treatments, including carbonitriding. These additives may chemically attack the carbonitride layer, leading to degradation and loss of the protective coating.
2. Surface Damage: The reactive nature of EP additives in GL-5 gear oils can cause surface damage to carbon-coated gears, including wear, scoring, and pitting. This damage compromises the integrity of the carbonitride layer, reducing its effectiveness in providing wear resistance and friction reduction.
3. Loss of Performance: The use of GL-5 gear oils with carbon-coated gears may result in reduced gear performance and service life. Surface damage and degradation of the carbonitride layer can lead to increased friction, heat generation, and wear, ultimately leading to premature gear failure and decreased operational reliability.

To mitigate the risk of damage to carbon-coated gears when using gear lubricants, including GL-5 oils, it’s essential to consider the following:

1. Select Suitable Lubricants: Choose gear oils specifically formulated for use with carbon-coated gears. These lubricants typically have lower levels of EP additives and are designed to provide lubrication without compromising the integrity of the surface treatment. For example, Vertex Torqgear AMT SYN 75W-90 has been manufactured to meet the Volvo 97315 specification which is suitable for carbon-coated gears in approved transmissions.
2. Consult Gear Manufacturer Recommendations: Follow the gear oil recommendations provided by the OEM to ensure compatibility and optimal performance. Consult the Vertex Lube Guide for suitable fluids which can accessed via the Vertex Lube Guide App or the link provided on our webpage. The Vertex Lube Guide can also be accessed via the link: https://www.datateck.com.au/Lube/LubricantsNZ/
3. Monitor Gear Condition: Regular inspection and monitoring of gear condition are essential to detect any signs of wear, damage, or lubricant-induced issues. Implement proactive maintenance practices, such as oil analysis and gear inspections, to identify potential problems early and take corrective action as needed.

In summary, while GL-5 gear oils offer excellent EP protection and load-carrying capacity, they may not be suitable for use with carbon-coated gears due to the potential for damage to the surface treatment. By selecting suitable lubricants, following manufacturer recommendations, and monitoring gear condition, operators can ensure the reliable performance and longevity of carbon-coated gear systems. It must be noted that GL-5 Gear Lubricants are not compatible with Brass or Bronze gears irrespective of the addition of a carbonitride layer.

Viscosity in Gear Oil Lubricants

Viscosity is one of the most important properties of gear oil lubricants, as it directly affects the ability to provide effective lubrication, reduce wear, and ensure smooth operation of gear systems. Viscosity refers to a fluid’s resistance to flow. Thicker (higher viscosity) oils flow more slowly, while thinner (lower viscosity) oils flow more easily.

Understanding Gear Oil Viscosity Grades

Gear oil viscosities are classified using the SAE J306 standard, which defines viscosity grades for automotive gear lubricants. These grades are designated by numbers such as 75W-90, 75W-140, or 85W-140.

The SAE J306 table below outlines the viscosity requirements for different gear oil grades:

The first number, followed by a “W” (winter), indicates the oil’s low-temperature performance. Lower numbers equate to thinner oil which flows better in cold conditions.

The second number represents the oil’s viscosity at high operating temperatures, ensuring sufficient lubrication under load.

For example, Vertex Transgear FE SYN 75W-90 gear oil remains fluid at lower temperatures compared to a Vertex Transgear 5 85W-140, making it suitable for colder climates or applications requiring easier cold weather operation.

Why Viscosity Matters

Protection Against Wear

Adequate viscosity maintains a protective film between gear teeth, reducing metal-to-metal contact and preventing wear.

Temperature Stability

A properly selected viscosity grade ensures the oil remains effective across a wide range of operating temperatures.

Efficiency and Performance

Using the correct viscosity minimises power losses due to excessive fluid drag while ensuring smooth operation.

Comparing Gear Oil Viscosity to Engine Oils

Gear oils typically have higher viscosities than engine oils because gears operate under higher loads and require a thicker lubricating film. However, the viscosity grades of gear oils and engine oils are not directly comparable. For example, an SAE 90 gear oil has a viscosity similar to an SAE 40 or 50 engine oil, even though the numbers appear different.

Selecting the right gear oil viscosity is essential for maintaining the longevity and performance of gear-driven systems. Always refer to manufacturer recommendations when choosing the appropriate viscosity grade for specific applications.

Appendix:

Copper Strip Corrosion Test – ASTM D130

The Copper Strip Corrosion Test (ASTM D130) tests the corrosive properties of Gear Lubricants. The test strip is immersed into the Gear Lubricant and tested at 40⁰C and 100⁰C. Most testing is limited to 100⁰C for 3 hours as increased temperatures accelerate copper corrosion. If little to no staining occurs at strip section 1a, then the gear lubricant is considered safe to use for brass or bronze gears. NB: the test is not indicative of carbon-coated gear suitability. Staining from 1b to 4c is indicative of EP induced metal corrosion. Figure 2 below shows a typical Copper Strip Corrosion Test Kit.

Figure 2 Copper Strip Corrosion Test Kit

Viscosity is one of the most important properties of a lubricant. It determines how easily the oil flows, affects wear protection, and influences energy efficiency. Selecting the right viscosity ensures that machinery operates smoothly under different conditions. This article will explain viscosity in simple terms, referencing key standards such as SAE J300, SAE J306, and ISO 3448. Tables have been included to illustrate viscosity classifications and comparisons across different lubricant types.

What is Viscosity?

Viscosity is a measure of a fluid’s resistance to flow. A higher viscosity means a thicker fluid that flows more slowly, while a lower viscosity means a thinner fluid that flows more easily. There are two main types of viscosity measurements:

Kinematic Viscosity

Measured in mm²/s (square millimetres per second) or centistokes (cSt), it describes how fast a fluid flows under gravity. The standard test method is ASTM D445.

Dynamic Viscosity

Measured in millipascal-seconds (mPa·s) or centipoise (cP), it quantifies a fluid’s internal resistance to flow when force is applied. The standard test method is ASTM D2983.

Kinematic viscosity is typically used to classify lubricants, while dynamic viscosity is important for cold-start performance and gear oils.

Monograde vs. Multigrade Oils

Lubricants can be classified into monograde and multigrade oils based on their viscosity behaviour across temperature ranges.

Monograde Oils

These oils have a fixed viscosity at a specific temperature and do not include viscosity modifiers. Examples include Vertex Magna DD 40 diesel engine oil, and Vertex TDH 80W Agricultural Transmission / hydraulic / gear oil. Monogrades are generally used in applications where high load conditions may cause shearing (degradation) of the viscosity modifier. Monograde oils are generally not suitable for applications where wide temperature ranges are experienced.

Multigrade Oils

These oils contain viscosity modifiers (also called viscosity index improvers), allowing them to perform effectively across a wider temperature range. For example, Vertex DX-1 5W-30 oil behaves like an SAE 5W oil at low temperatures, ensuring good cold-start performance, and like an SAE 30 oil at high temperatures, providing adequate protection.

Role of Viscosity Modifiers

Viscosity modifiers are polymer additives that expand and contract depending on temperature:

• At low temperatures, the polymers contract, allowing the oil to flow easily for better startup lubrication.
• At high temperatures, the polymers expand, increasing resistance to flow and maintaining sufficient viscosity for engine protection.

Viscosity modifiers enable modern lubricants to provide better fuel efficiency, reduce wear, and improve overall engine performance. They are particularly important in high-performance and fuel-efficient engine oils.

Viscosity Classification Systems

Several international standards define viscosity grades for different lubricant applications. The tables below provide a detailed breakdown of these classifications.

Comparative Table of Kinematic and Dynamic Viscosity

For illustrative purposes, the following table compares kinematic viscosity (mm²/s, cSt) and dynamic viscosity (mPa·s, cP) for various lubricants and fluids at typical operating temperatures:

SAE J300 – Engine Oil Viscosity Grades

SAE J300 defines viscosity grades for engine oils, including both winter grades (e.g., 0W, 5W, 10W) and high-temperature grades (e.g., 30, 40, 50). Winter grades are designed for cold starts, while high-temperature grades ensure proper protection during operation.

The “W” in winter grades stands for “Winter”, indicating performance at low temperatures.

Vertex LS 5W-30 oil, for example, flows well at low temperatures (5W) and provides adequate viscosity at 100°C (30 grade).

Cold-cranking viscosity, measured using ASTM D5293, ensures the oil remains fluid enough for engine startup in winter conditions.

The table below provides the official SAE J300 classifications:

* 0W-40, 5W-40 & 10W-40 grades

** 15W-40, 20W-40, 25W-40 & 40 grades

Cold Cranking and Low-Temperature Performance

Cold cranking is a critical factor for engine oils, particularly in regions with low ambient temperatures. When an engine starts in cold weather, the oil must be fluid enough to circulate quickly and provide lubrication. The Cold Cranking Simulator (CCS) test (ASTM D5293) measures the oil’s viscosity at -10°C to -35°C, depending on the winter grade.

• Lower CCS viscosity values indicate better cold-start performance.
• Oils with high CCS values may cause difficult startups, excessive engine wear, or battery drain.

For example, a 0W oil has lower cold-cranking resistance than a 10W oil, making it more suitable for extreme winter conditions.

SAE J306 – Gear Oil Viscosity Grades

Gear oils use the SAE J306 standard, which categorises oils based on their viscosity at 100°C and their performance at low temperatures. Unlike engine oils, gear oils generally have higher viscosity levels.

Vertex FE SYN 75W-90 gear oil remains fluid in cold conditions (75W) and maintains proper lubrication at high temperatures (90 grade).

The low-temperature viscosity is measured using a Brookfield viscometer (ASTM D2983) to ensure smooth gear shifting in cold weather.

The SAE J306 table below outlines the viscosity requirements for different gear oil grades:

ISO 3448 – Industrial Oil Viscosity Grades

Industrial oils, such as hydraulic oils and industrial gear oils, follow the ISO 3448 standard, which classifies lubricants by their kinematic viscosity at 40°C.

Common grades include ISO VG 32, ISO VG 46, ISO VG 68, and ISO VG 220.

For example, Vertex Hytec AW 46 means the oil has a kinematic viscosity of approximately 46 mm²/s (or cSt) at 40°C.

The following table lists the standard ISO 3448 viscosity grades:

Comparative Table of Viscosities: SAE J300 / SAE J306 and ISO 3448

The following table provides a visual reference of the corresponding viscosities of engine oils, gear oils and industrial oils. Note: increases in values provide a corresponding increase in viscosities.

Why is Viscosity Important?

Choosing the right viscosity is essential for lubricant performance:

Low viscosity oils (e.g., Vertex Expert FE 0W-20 engine oil) reduce internal friction, improving fuel economy and cold-start performance.

High viscosity oils (e.g., Vertex Transgear SYN FE 75W-140 gear oil) provide better protection under high loads and extreme temperatures.

Cold-cranking performance ensures engines start easily in winter conditions, preventing wear during startup.

Conclusion

Understanding viscosity helps users select the right lubricant for their vehicles, machinery, and industrial applications. Whether considering engine oils (SAE J300), gear oils (SAE J306), or industrial lubricants (ISO 3448), viscosity plays a key role in ensuring proper lubrication and efficiency. The tables provided offer a reference point for selecting the correct viscosity grade based on your specific needs.

For specific product recommendations, always refer to the manufacturer’s guidelines and the viscosity classifications relevant to your equipment.