Tagged: lubricants

Lubrication Explained

What is Lubrication?

Lubrication is the process of reducing friction, wear, and heat between moving surfaces by introducing a lubricating substance, such as oil or grease.

The Purpose of Lubrication

If you walk into any industrial facility, you will find lubricants. While they come in all types of textures (greases or oils), viscosities, and packaging, one thing remains true: We need them. Lubricants were designed to reduce friction as their main function. However, that’s not their only use.

Although lubricants can effectively reduce friction, they can also reduce or transfer the heat built up in machines. This only applies to oils circulated through the systems and not grease that remains in place.

Additionally, lubricants can minimize wear by providing an adequate film to separate surfaces from rubbing on each other.

The 6 Functions of a Lubricant

Lubricants also help improve the efficiency of the machine by removing heat and reducing friction. They can also remove contaminants (for oils that are circulating, not grease) and transport them away from the machine’s internals. This is due to some additive technologies (such as dispersants or detergents).

Depending on the type of lubricant or its application, its function can also change. For instance, hydraulic oils are specifically used to transmit power, something that gear oils or motor oils cannot do. On the other hand, the lubricant can be considered a conduit of information if condition monitoring is considered.

Lubricants provide several functions depending on their application and environment. However, the main functions of a lubricant include reducing friction and wear, distributing heat, removing contaminants, and improving efficiency.

How Lubrication Reduces Friction and Wear

At the heart of lubrication is the main function of overcoming friction. When two parts move or two surfaces rub against each other, microscopic projections called asperities exist. Even on what appears to be smooth surfaces, asperities exist, and when these move over each other, friction is produced, which in turn can generate heat and cause wear.

Wear can typically occur in various forms, but in many of these, the touching of the asperities serves as the trigger point for wear to occur.

This is where lubricants really make a statement. They serve to provide a barrier between the two surfaces, almost allowing them to float over each other seamlessly. As such, friction is reduced once the asperities are kept apart, and this even influences a reduction in the occurrence of wear.

Wear can typically occur in various forms, but in many of these, the touching of the asperities serves as the trigger point for wear to occur. With the presence of the appropriate viscosity of lubricants, these asperities can be kept apart, and the occurrence of wear can be diminished significantly.

The Role of Lubrication in Preventive Maintenance

As we have noted above, proper lubrication can help to prevent wear. This is one of the many characteristics which make it ideally suited as a tool for preventive maintenance.

As defined, preventive maintenance can help maintenance professionals schedule time-based tasks / prescribed intervals¹. Any maintenance manual will include prescribed intervals at which lubricants should be changed (typically after 500 hours or 5000km).

OEMs (Original Equipment Manufacturers) defined these intervals as general guidelines for machine operators. This gives operators an idea of the lubricant’s expected life or the duration after which it would no longer be able to perform its functions adequately. By changing the lubricants at these intervals, one could avoid unplanned downtime.

Another aspect of lubrication associated with preventive maintenance is relubrication intervals. In some machines, there are minimum required reservoir levels that need to be maintained.

However, depending on the system, there may be some expected loss of lubricants during its lifetime. As such, relubrication intervals can help prevent unwanted downtime by injecting new oil or grease (with fresh additives) and maintaining the required reservoir levels.

Find out more in the full article featured in Precision Lubrication Magazine.

Oil Properties / Storage & Handling of Lubricants

Storage and Handling & Advancements in Hydraulic oils

Hydraulic systems have smaller clearances than many. As such, it is imperative that these oils be kept clean and free from any debris. Most hydraulic components have a required ISO 4406 rating that should be met to ensure that the oils do not allow foreign particles to enter as these can easily clog the clearances and cause the system to stop working.

Chevron Lubricants produced a document that compiles some ISO 4406 codes for various types of industrial off highway equipment, which also includes the hydraulic standards. It noted the recommended ISO Cleanliness for John Deere hydraulic Excavators can be ≤23/21/16, this can be found here (Chevron Lubricants, 2015).

Hydraulic oils should be pre-filtered before being placed in your equipment even though there are filters on the inside of the equipment by reducing the amount of contamination entering the system from the onset, you can ensure a longer life for your hydraulic oil. Hydraulic oils should also be stored in closed containers not those that are left open to the atmosphere!

Advancements in Hydraulic Oils

According to (Fitzpatrick & Thom, 2021), the hydraulic oil market was approximately worth USD 77.5 billion by the end of 2021. Mobile hydraulics account for 65% of the market while industrial equipment represents 35% of the market. Clearly, the larger market share exists for mobile hydraulics. However, OEMs are also moving towards smaller oil sumps with longer oil drain intervals that can impact on the volume of hydraulics needed periodically.

Changes by OEMs also impact the formulation of hydraulic oils. For instance, if a smaller sump is used then, the hydraulic oil must now be able to cool faster, transport the same (or larger) force and maintain the intended viscosity of operation while being under greater stress. In these cases, the additive packages involving the antiwear, thermal stability, viscosity index improvers, defoamants and dispersants must be formulated to work in unison without compromising the other.

There have been changes in additive technology that allow for larger tolerances for various characteristics but while additives are evolving, the refining of base oils is also trying to keep up. With all of these evolutions, the chemical composition of hydraulic oil today vastly differs from one created in the 1950s. The requirements of hydraulic oil have also greatly evolved, forcing these changes in formulation.

Hydraulic oils today need to provide longer oil drain intervals, better stick/slip characteristics, increased efficiency, improved conductivity and wear performance and an added level of sustainability. Formulators need to create hydraulic oils that can adhere to these characteristics while also not infringing on regulatory requirements. This makes hydraulic oils one of the most powerful types of oils because they must conform to these requirements while also transferring force from one place to another.

References

Chevron Lubricants. (2015, January 24). Chevron Lubricants Latin America. Retrieved from Chevron Lubricants: https://latinamerica.chevronlubricants.com

Fitzpatrick, A., & Thom, M. (2021, November 08). How the Global Hydraulic Fluid Market Is Changing—And What It Means for the Future. Retrieved from Power Transmission Engineering: https://www.powertransmission.com/blogs/1-revolutions/post/189

Mang, T., & Dresel, W. (2007). Lubricants and Lubrication Second Edition. Weinheim: WILEY-VCH.

Pirro, D. M., Webster, M., & Daschner, E. (2016). Lubrication Fundamentals, Third Edition Revised and Expanded, ExxonMobil. Boca Raton: CRC Press, Taylor & Francis Group.

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Oil Properties

Are Consolidation and Cheaper Hydraulic Oils Worthwhile Considerations?

Given the various types of hydraulic oils that exist, can they all be consolidated into one hydraulic oil that can serve the purpose for all the applications? The short answer is no, the longer answer is that if there is overlap among OEM recommendations within the same viscosity, then there is a possibility of consolidation. Typically, OEMs will provide guidelines on the oils recommended for use and they should be sought out for these consolidations as they will be more familiar with compatibility issues, as well.

On the other hand, it may mean that the hydraulic storage area of the warehouse has numerous hydraulic oils. In this case, a proper labelling system should be in place to ensure that the correct oil gets to the right location. Since these are specialized, using an incorrect oil (or an oil that does not meet the right specification) can result in disastrous outcomes for the equipment especially for compatibility challenges.

Are Consolidation and Cheaper Hydraulic Oils Worthwhile Considerations

One of the most common issues with hydraulic equipment is the existence of leaks. Depending on the application, some owners prefer not to fix the leaks and use cheap hydraulic oil to keep the equipment working. However, this is not the best practice.

When hydraulic oil leaks out into the environment, this can be hazardous to the people on the site (spills or trips), equipment (skids or contamination) and the environment since it was not disposed of properly. By using cheap oil, this can also damage the equipment even more as that oil may not meet the OEM requirements. In these cases, more harm is being done to the environment and the equipment and there can be significant losses financially and operationally.

This is where the quality of the oil and operations (no leaks) can trump quantity (excess volumes of cheaper oil). Unless the leaks are fixed, then the volume of cheaper oil will continue to increase and there will be additional labour costs to constantly maintain the sump levels as well as delays to the project.

Therefore, the overall impact on the efficiency of the hydraulic equipment will be reduced. However, if the leaks are fixed and a quality hydraulic oil is used, then the machine can operate more efficiently, complete the assigned projects and possibly even reduce extra labour costs related to maintenance.

Ideally, consolidation can be achieved as long as the OEM requirements are being fulfilled. However, cheaper oil that does not meet the required OEM standard for a particular piece of equipment is not an ideal option as it can cause more harm than good in the long run.

Find out more about the article featured in Equipment Today Magazine.

Oil Properties

Are There Different Types of Hydraulic Oils?

Similar to there being endless types of greases, there are also many types of hydraulic oils specifically designed for certain systems. Hydraulics comprise of lots of different operations as such, they will be called upon to perform in various applications. Some of these can include being fire resistant, biodegradable or even being able to also act as an engine oil. These properties can be influenced by the type of base oil used to produce these oils. For example, fire resistant or rapidly biodegradable fluids or even specialty hydraulic fluids can use PAOs (Polyalphaolefins), PAGs (Polyalkylglycols), POE (ester oils) or other synthetic oils as their base oil.

As per (Mang & Dresel, 2007), hydraulics require special types of additives for their applications. The most important additives for hydraulic oils are:

“Surface active additives” – For hydraulic oils these can be rust inhibitors, metal deactivators, wear inhibitors, friction modifiers, detergents / dispersants, etc.

“Base Oil active additives” – For hydraulic oils, these can be antioxidants, defoamers, VI Improvers, Pourpoint improvers, etc.

Typically, the additives for hydraulic oils can be broadly classed into those which contain zinc and ash and those which do not. Zinc and Ash free oils can represent 20-30% of hydraulic oils on the market and are used for specialty applications where the presence of zinc or ash can hamper the functionality of the equipment.

One such example is the use of these oils in the JCB Fastrac 3000 series for the hydraulic oils. These systems contain yellow metals which can be easily degraded with the presence of zinc or the filterability of the oil can be impacted due to the presence of water. Hence, zinc and ash free oils must be used in these instances.

The following shows a chart of the types of hydraulic fluids as per (Mang & Dresel, 2007) broken down by hydrokinetic applications, hydrostatic applications and mobile systems.

Figure 1: Classifications of hydraulic fluids as per (Mang & Dresel, 2007) Chapter 11, figure 11.9.

As seen above, there are many different classifications of hydraulic oils. To provide some clarification on the symbols used in DIN 51 502 and ISO 6743/4, (Mang & Dresel, 2007) produced this table.

Figure 2: Classification of mineral oil-based hydraulic fluids as per (Mang & Dresel, 2007), Chapter 11, Table 11.3.

When looking at hydraulic oil classifications, these categories will come up and it is important to be able to understand what each of these mean as well as how it translates to your system. Typically, the most common are the ISO HM and ISO HV.

The ISO HM refers to oils with improved anti-wear properties used in general hydraulic systems with highly loaded components and where there is a need for good water separation operating in the range of -20 to 90°C.

The ISO HV oils are HM oils with additives that improve viscosity-temperature behavior. Ideally, these are used in environments that experience significant changes in temperatures, such as construction or marine, between the ranges of -35 to 120°C.

Find out more about the article featured in Equipment Today Magazine.

Oil Properties

What Are The Functions of Hydraulic Oils?

Hydraulic oils are used in many areas of our life, from the telescopic booms of cranes to the control valves in a tractor. These oils are special as they perform a particular function which is unique to them. In addition to the regular functions of an oil, hydraulic oils can transmit power which truly sets them apart. In this article, we will take a deeper dive into the world of hydraulic oils, how they can be used, ways that they should be stored and handled and of course some advancements that we’ve seen over the years.

What Are The Functions of Hydraulic Oils?

Before going any further, we must understand how hydraulic oils function and the impact that they create for our equipment. As per (Pirro, Webster, & Daschner, 2016), the concept of hydraulics revolves around the transmission of force from one point to another where the fluid is the transmitter of this force. Ideally, this is based off Pascal’s Law where, “The pressure applied to a confined fluid is transmitted undiminished in all directions and acts with equal force and at right angles to them.”

As applied to hydraulic oils, once a force is exerted on an oil, the oil can transmit this force to either help an actuator turn or stop an excavator from moving (through braking). This is the transmission of pressure, but hydraulic oils can also provide the functions of reduced wear, prevention of rust and corrosion, reduction in wear and friction and an overall improvement in system efficiency.

For anyone who has worked with hydraulic oils, they will be familiar with the fact that these oils have very tight clearances which requires them to be clean. As they are transmitting power through the fluid, having clean hydraulic oil is essential, so this flow is not disrupted. Since the force will be the same throughout the lubricant, having these tighter clearances allows for more force to be output per square area at the intended target without the contaminants.

Overall, hydraulics will perform the regular functions of an oil but with the added benefit of the transmission of force for these applications. But not all hydraulic oils are created equally and some need to be specifically designed for particular applications within our industry.

Find out more about the article featured in Equipment Today Magazine.

Oil Properties

Understanding the oil analysis results of Diesel Engine Oil

Having the information above is great to understand how your diesel engine oil degrades, but how will you know that it is degrading? One of the most reputable ways is to submit your oil for testing in the lab. Depending on the type of diesel engine (on-highway, marine or off-highway), different tests will be involved. However, here are the basic ones that you should be familiar with.

When determining the health of your diesel engine oil, the first thing to check is the oil’s viscosity, total base number (TBN), whether all the additives are at the correct levels, if there are any wear metals or contaminants present and finally the presence of water or fuel dilution as shown in Figure 3.

Figure 3: Basic oil analysis tests for your diesel engine

Viscosity (American Society for Testing and Materials D445) – The viscosity levels should ideally fall within ±5% of the original value. If they exceed ±10% of the original value, then the levels will fall out of the classification for that grade of oil.

For instance, Mobil Delvac 15w40’s kinematic viscosity, at 100°C, is 15.6 millimeters squared per second (mm²/s), according to its technical data sheet. If this value drops below 14.04 mm²/s or above 17.16 mm²/s then it can no longer be classed as a 15w40 oil and will not be able to properly lubricate the engine. These values vary depending on the manufacturer, application of the oil and the lab being used. These are a guideline in this example.

TBN– This is the amount of alkalinity remaining in the oil. The oil’s alkalinity helps neutralize the acids formed in a diesel engine. This value is always depleting as acids are continuously forming in an engine. However, if the TBN value drops below 40% to 50%, then there isn’t much reserve left to continue to protect the oil. This is the threshold limit, which can vary depending on the application, but this is a good guide to follow.

Additives – All finished lubricants have additive packages. These will vary depending on the oil producer. However, a few additives should be on your radar when trending their depletion in diesel engine oils. These include zinc, phosphorus, magnesium and calcium. These additives typically form parts of the dispersant, corrosion and antiwear additives that protect the oil. Ideally trending the decline of these may be helpful but your lab would have reference values (based on the type of oil) and can advise on concerning levels.

Wear metals – During the engine's lifetime, components will wear. Depending on the engine’s manufacturer, the warning limits will also vary (this also differs depending on the application). Iron, aluminum, chromium, copper, lead, molybdenum and tin are some metals to trend. If other special metals are in your engine, then you can ask your lab to include them in the oil analysis report. Typically, if there is an upward trend, this indicates wear/damage of specific components.

Operators can perform a simple test to determine if metal filings are in their oil (indicating some form of wear). They can place the oil in a shallow container and then place a magnet below the container or place the magnet in a sealed plastic bag and immerse it into the container. When the magnet is removed, if there are metal filings on the magnet, then this indicates the presence of wear metals, and the mechanic should begin investigating for damaged components.

Contaminants– These include any material which is foreign to the lubricant. Typically, labs test for the presence of sodium and silicon. Depending on the application’s environment, these values can increase indicating that they are entering the system somehow. Usually, this can occur during lubricant top-ups or improper storage and handling practices.

Presence of water – This is never a good sign because water can affect the lubricant by changing its overall viscosity, bleaching out some of the additives and even acting as a catalyst. Many labs perform a crackle test (where the oil is heated and if it produces a “pop” sound, then that confirms water in the lubricant. In certain instances, it is obvious that there is water present because it settles out in the sump/container. Labs can also perform a test to quantify the volume of water present. Typically, 2,000 ppm to 5,000 ppm is too much for most applications but this varies depending on the manufacturer.

Operators can perform their version of the crackle test by placing some of the oil in a metal spoon and heating it with a flame. If it produces a pop, then they can confirm that the oil has too much water in it before sending it off to the lab. Note: This should not be done in a highly flammable environment!

Fuel dilution – This occurs in most diesel engines due to the nature of the engine. However, limits need to be adhered to because too much fuel in the oil can lead to drastic changes in its viscosity. Usually, this value should not exceed 6%, but this can vary depending on the application and the manufacturer.

One way that operators can find out if there is fuel in their oil is to place a small drop of the oil on a coffee filter and leave it to “dry” for some time. The oil will spread out in concentric rings and if there is fuel present, there will be a rainbow ring. This means that the mechanics need to figure out if there is an issue with any of the injectors or seals in the diesel engine.

Ideally, the main idea with oil analysis is to develop a trend for your equipment and understand how the values align over time. This can help operators spot if an inaccurate sample was taken (possibly after a top-up, directly after an oil change or even from the bottom of the sump). An analysis also assists in planning the maintenance of components. For instance, if the value of iron in the oil analysis report keeps increasing then there is a strong possibility that some iron component is wearing. This can give the mechanic the time they need to investigate the engine and replace the component before it causes unscheduled downtime.

Protect One of Your Greatest Assets

Your diesel engine oil is one of the greatest assets in your fleet. You should be able to use an oil that aligns with your application while slowing its degradation rate with good practices and managing its health. Diesel engine oils form a critical part of your operation and deserve attention.

References

American Petroleum Institute. (November 18, 2016). New API Certified CK-4 and FA-4 Diesel Engine Oils are Available Beginning December 1. Retrieved from API: https://www.api.org/news-policy-and-issues/news/2016/11/18/new-api-certified-diesel-engine-oils-are

American Petroleum Institute. (February 19, 2024). API's Motor Oil Guide. Retrieved from API: https://www.api.org/-/media/files/certification/engine-oil-diesel/publications/motor%20oil%20guide%201020.pdf

The International Council on Combustion Engines. (2004). Guidelines for diesel engines lubrication - Oil Degradation | Number 22. CIMAC.

Want to read the entire article? Find it here in Equipment Today Magazine.

equip-today - evolution-diesel-June-horz

Oil Properties

Why Does My Diesel Engine Oil Degrade?

All oils degrade over time. They can be considered consumable items as they must be replaced over time. Diesel engine oils are no different except that they may be susceptible to certain mechanisms that turbine oils are not. The diesel engine is often placed under a lot of pressure to deliver power while keeping cool and managing emissions.

The critical areas for lubricant performance in a diesel engine usually include:

Viscosity control
Alkalinity retention, base number (BN)
Engine cleanliness control
Insoluble control
Wear protection
Oxidation stability
Nitration

Typically, these factors are monitored in these types of oils to ensure that they remain in a healthy condition.

Several factors affect oil degradation in a diesel engine. According to The International Council on Combustion Engines (The International Council on Combustion Engines, 2004), these include specific lube oil consumption; specific lube oil capacity; system oil circulation speed; NOx content in the crankcase atmosphere; and influence on the lubricant, fuel contamination in trunk piston engines, deposition tendency on the cylinder liner wall, metals in lubricant systems, and oil top-up intervals. These can further be divided into systemic conditions (which cannot be easily altered) and environmental conditions (because of processes occurring within or to the system) as shown in Figure 2.

Figure 2: Systemic & Environmental Conditions which affect degradation of diesel engine oil

Systemic Conditions

While lubricant degradation can be caused by environmental strains being placed on the lubricant, there are times when the operating design of the system also encourages degradation. Three such cases for diesel engine oils are specific lube oil consumption, specific lube oil capacity and system oil circulation speed.

Specific lube oil consumption (SLOC, g/kWh) is defined as the oil consumption in grams per hour per unit of output in kilowatts (kW) of the engine (The International Council on Combustion Engines, 2004). Over the years, there has been a reduction in the SLOC for engines with special rings inset into the upper part of the cylinder liner. These reduce the rubbing of the crown land against the cylinder liner surface.

With reduced oil consumption, oil top-ups, which would have introduced fresh oil into the system, are consequently reduced. This fresh oil would have increased the presence of additives and helped in maintaining the required viscosity of the current oil. However, since the SLOC is reduced, the oil does not get a “boost” during its lifespan and will continue to degrade at its current rate. Hence, a lower SLOC may encourage the degradation of diesel engine oil.

Specific lube oil capacity, also known as the sump size, which is the nominal quantity in kilograms (kg) of lubricant circulated in the engine per unit of output in kW. According to The International Council on Combustion Engines, the specific oil capacity does not directly affect the equilibrium level of degradation. However, it can influence the rate at which deterioration occurs as smaller sump sizes can increase the rate at which degradation achieves an equilibrium level. Typically for dry sump designs, the specific oil capacity is around 0.5 kg/kW to 1.5 kg/kW. These values are closer to 0.1 kg/kW to 1.0 kg/kW for wet sumps.

System oil circulation speed refers to the time taken for one circulation of the total bulk oil. In diesel engines, lubricants are usually subjected to blow-by gas (including soot and NOx) during their time in the crankcase. If the lubricant spends a longer time in the crankcase, it can become degraded at a faster rate. Typically, the time required for one circulation of bulk oil averages between 1.5 minutes to 6 minutes. However, we have seen the trend toward smaller sump sizes and, by extension, shorter circulation times, which should reduce the degradation rate.

Environmental Conditions

The environmental conditions that lubricants must endure can also influence their degradation. These conditions can either be enforced through the system, its operating conditions or from conditions outside the system. There are a few environmental conditions which must be addressed (The International Council on Combustion Engines, 2004).

NOx content in the crankcase atmosphere and influence on the lubricant has more applicability to gasoline engines compared to diesel engines but they should not be fully ruled out. Diesel engines are more susceptible to sulfur-derived acids (caused by the burning of diesel fuel). However, NOx can be produced by the oxidation of atmospheric nitrogen during combustion, which can affect degradation.

Field studies show a correlation between nitration levels, an increase in viscosity and an increase in acid in the oil. NOx can also behave as a precursor and catalyst that promotes oxidation through the formation of free radicals in the lubricant. On the other hand, there can be direct nitration of the lubricant and its oxidation products to produce soluble nitrates and nitro compounds. These can eventually polymerize to form similar by-products of oxidation. This can lead to increased acidity (lowering the BN) and increased viscosity of the lubricant.

Fuel contamination in trunk piston engines happens quite often in diesel engines. If the fuel injectors are defective or the seals do not effectively seal to keep fuel out, fuel enters the oil. When fuel is in the oil, oil can become degraded quickly, often causing the viscosity to reduce to a value that compromises the ability of the oil to form a protective layer inside the component. The fuel dilution test can quantify the content of fuel in the oil. Depending on the type of engine, the tolerance levels will differ.

Deposition tendency on the cylinder liner wall is usually caused by unburnt fuel or excess oil in this area or the chamber. Typically, the piston rings scrape these deposits back into the oil, leading to an increase in the volume of insolubles. This also increases the viscosity of the oil, and it appears a darker color.

Reducing the SLOC also decreases the deposits on the liner wall because special rings (near the top of the liner) are installed to have controlled clearance of the piston crown. This reduces the crown land deposit which can also minimize bore polish and hot carbon wiping.

In addition, with a reduction in SLOC, the number of oil top ups is also reduced. As such, the replenishment rate of additives (in particular the BN) is not as frequent. Therefore, the degradation of the oil will advance at a slightly faster rate due to the lower SLOC which affects the rate of top up.

Metals in lubricant systems can also act as a catalyst for the degradation of the oil. During the oxidation process, copper is one of the most common catalysts in addition to other wear metals (such as iron) which can increase the rates of oxidation. As such, the presence of these metals increases the degradation rate as well.

Oil top-up intervals must be managed in such a way that it does not disturb the balance of the system. Typically, when the sump level falls below 90% to 95% (depending on the manufacturer), a top-up is needed. When fresh oil enters the system, it replenishes some additives and breathes new life into the oil. However, with this change in temperature of new oil coming into the system (especially in large quantities of about 15%), the deposits held in suspension tend to precipitate.

Additionally, foaming (caused by the increased concentration of some additives) can occur if too much fresh oil is added at once. As such, oil top-up intervals must be managed to avoid further degradation.

Want to read the entire article? Find it here in Equipment Today Magazine.

Oil Properties

The Evolution of Diesel Engine oil CK4 vs FA4

As engines have evolved, the lubricants that keep them running have changed with them.

Diesel engines have been around for more than half a century. Chances are that if you are around fleets or equipment, you have encountered a diesel engine. They have been described as the workhorses of the industry, and they provide users across industries with the power they need. Whether it’s in the form of a generator for a medical facility, a tractor engine on a farm or an engine on a school bus, diesel engines are everywhere.

Diesel engines have evolved, and a diesel engine today may not exactly line up with the diesel engines of the past. However, their evolution has been slower than that of the gasoline engine. For instance, many diesel engines today still use a 40-weight oil (albeit multigrade or semi-synthetic) which can tell us about the changes in the viscosity requirements over the years.

This column explores how the specifications changed to get a better idea of:

The evolution of diesel engine oils
Some reasons behind its degradation
Ways that degradation sources can be identified through oil analysis

Understanding Diesel Engine Oil Specifications

As per the American Petroleum Institute (API), the standards governing Diesel Engine oils began with the CA spec which became obsolete in 1959. The latest diesel engine oil standards were upgraded to CK4 and FA4 in December 2016. On the other hand, the gasoline spec entered its latest standard, the SP spec which includes 0w16 and 5w16, in May 2020.

What Does This Mean for Your Fleet?

Most API standards are backward compatible. This means that an engine that requires a CJ4 spec oil can still use a CK4 spec oil, but the reverse is not true.

For more modern engines, oils have been engineered following environmental regulations that did not exist 50 years ago. Additionally, these newer engines now have more demand compared to older engines.

As such, the oil is under more duress and must perform under these conditions. Newer oils are formulated with this in mind.

CK4 oils provide enhanced protection against oil oxidation and viscosity loss caused by shear and oil aeration, catalyst poisoning, particulate filter blocking, engine wear, piston deposits, degradation of low- and high-temperature properties, and soot-related viscosity increase compared to the CJ4 oils (API, 2024). It must be noted that FA4 oils are not backward compatible with the CJ4 oils nor are they intended for on- or off-highway applications which require CJ4 oils.

The Evolution of Diesel Engine oil CK4 vs FA4

The FA4 oils are blended to a high-temperature, high-shear (HTHS) viscosity range of 2.9 centipoise (cP) to 3.2 cP to assist in reducing greenhouse gas emissions. They are especially effective at sustaining emission control system durability where particulate filters and other advanced aftertreatment systems are used.

These oils also provide enhanced protection against oil oxidation and viscosity loss caused by shear and oil aeration. In addition, they protect against catalyst poisoning, particulate filter blocking, engine wear, piston deposits, degradation of low and high-temperature properties, and soot-related viscosity increase.

What’s the Difference Between CK4 & FA4 oils?

CK4 oils are specifically designed for use in high-speed, four-stroke-cycle diesel engines designed to meet the 2017 model year, on-highway and tier 4, non-road exhaust emission standards and for previous model year diesel engines. However, these are also formulated for diesel engines using diesel fuel ranging in sulfur content up to 500 parts per million (ppm) (0.05% by weight). Diesel fuels that contain more than 15 ppm (0.0015%) may impact the exhaust aftertreatment system’s durability and/or the oil drain interval.

On the other hand, FA4 oils are xW30 oils specifically designed for use in select high-speed, four-stroke-cycle diesel engines designed to meet 2017 model year, on-highway greenhouse gas emission standards. These are particularly formulated for diesel fuels with a sulfur content up to 15 ppm (0.0015% by weight).

API FA-4 oils are not interchangeable or backward compatible with API CK-4, CJ-4, CI-4, CI-4+ and CH-4 oils. Additionally, these oils cannot be used with diesel fuel containing between 500 ppm to 15 ppm of sulfur.

Figure 1 shows the API donut for both specifications as detailed by (API, 2016). This API donut typically appears on every diesel engine oil that is sold (those that are original and not counterfeit).

Figure 1: API donut. Source: American Petroleum Institute

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Lubricant Degradation

The Influence of Lubricant Selection on Degradation

Guidelines should always be followed when selecting a lubricant for a particular application. OEMs will have specific criteria ranges for specialty applications that must be satisfied. Some general guidelines which should be considered can be summarized in the table below based on the listed mechanisms above.

Based on the three listed mechanisms above, one can identify that choosing a lubricant can impact the type of degradation which occurs during its lifetime. As such, when selecting lubricants, it is critical to note their applications and the conditions they will endure.

Having a history of lubricant failures for particular equipment can also assist in this regard by informing users of past failure trends. Therefore, when selecting a lubricant, operators can be more mindful of the properties which should not be compromised during the selection process.

The process of troubleshooting degradation in lubricants has been covered in detail in the book, “Lubrication Degradation – Getting Into the Root Causes” by Bob Latino and myself, published by CRC Press, Taylor and Francis.

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Lubricant Degradation

Which Degradation Mechanism Is Affected?

My previous article published in Precision Lubrication covered six degradation mechanisms: oxidation, thermal degradation, microdieseling, electrostatic spark discharge, additive depletion, and contamination.

Upon further investigation, there are only three mechanisms where selecting the correct lubricant will impact the degradation mode. These are; oxidation, microdieseling, and electrostatic spark discharge. The properties of the lubricant can easily influence each of these degradation mechanisms.

When selecting a lubricant, especially for rotating equipment, one of the critical areas of importance is the performance of the antioxidants. When formulated, oils must be balanced to protect the components in various aspects.

Thus, some oils that boast a high level of antioxidants may suffer from low levels of antiwear, or these increased levels can react with other components to reduce the performance of the oil. During oxidation, antioxidants are depleted at an accelerated rate which can lead to lube oil varnish. Hence, the choice of lubricant can influence this degradation mechanism.

A good trending test, in this case, would be the RULER test to accurately quantify and trend the remaining useful antioxidants for the oil. This test can easily distinguish and quantify the type of antioxidant rather than providing an estimate of the oxidation, as with the RPVOT test.

It has been noted that oils with an RPVOT of more than 1000 mins have a low reproducibility value which can mislead users during trending of lubricant degradation. Corrosion inhibitors, not just antioxidants, have also influenced the RPVOT values. Thus, there are better tests for monitoring the presence of antioxidants and helping operators to detect the onset of possible lube oil varnish.

On the other hand, during microdieseling, entrained air can lead to pitting the equipment’s internals and eventually the production of sludge or tars depending on whether the entrained air experiences a high or low implosion pressure.

If bubbles become entrained in the lubricant and do not rise to the surface, this can directly result from the lubricant’s antifoaming property. The antifoaming property is essential when selecting an oil, especially for gearboxes. Typically, OEMs will have recommendations for their components that should be followed.

Another degradation mechanism that can be influenced by lubricant selection is electrostatic spark discharge. This mechanism occurs when the lubricant accumulates static electricity after passing through tight clearances. These then discharge at the filters or other components inside the equipment, providing sharp points or ideal areas to allow static discharge.

This is frequently seen in hydraulic oils due to the very tight clearances within the equipment. If fluid conductivity is above 100 pS/m, the risk of static being produced is reduced. Some OEMs also provide particular values the lubricant should meet for this property.

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