In two previous articles, we sketched some of the background of the GF-6 oil standard, and also provided some details of why a new oil standard was needed. In addition, we mentioned the fact that the main purpose of the GF-6 oil standard was to establish uniform specifications for engine oil formulation that are now designed specifically to reduce internal friction in modern engines to reduce both fuel consumption and harmful exhaust emissions.
However, as with all things automotive, the proverbial devil lies in the details, in this case, the details involve the relationship between any given oil formulation’s viscosity (resistance to flow), and the level of protection that oil formulation provides against boundary lubrication conditions, sludge formation, and corrosion. Thus, in this article, we will discuss the classification schemes within the GF-6 standard, which are designed to prevent the inappropriate use of some GF-6 oil formulations that could result in engine failures, but before we get to specifics, we need to discuss-
Although the demise of internal combustion engine technology is certain, at least as it pertains to internal combustion engines in light vehicles, nobody is quite sure how long fossil fuel-burning engines will be with us in markets such as ours, given the severe lack of infrastructure to support electric vehicles at meaningful scales.
What is also true is the fact that internal combustion technology has reached a plateau in terms of development. This means that no car manufacturer is going to embark on a hugely expensive research program to develop new technologies, materials, and control systems to produce more fuel-efficient engines- given that the demise of internal combustion engines is imminent in all major automotive markets.
Nonetheless, the imminent demise of internal combustion engines in light vehicles has not deterred environmental protection agencies from developing the most stringent exhaust emissions regulations to date. This iteration of the regulations, known as Euro 7, is expected to be introduced in 2025, and while it is still under construction it is also expected to be several orders of magnitude more stringent than the current Euro 6 regulations. As a point of interest, though, the Euro 7 regulations are also expected to be the last set of exhaust emissions regulations to be enacted before we see the death of internal combustion engine technology in light vehicles.
So, what does this have to do with oil viscosity? Simply this; since we will almost certainly see no further meaningful mechanical development of existing engines, the only thing engine designers have to work with to reduce friction to the point where modern engines might meet the expected Euro 7 regulations, is to reduce pumping losses by making oil flow through engines more easily. In practice, this means making oil much less resistant to flow than ever before, without sacrificing lubricity and corrosion protection, at the same time.
Balancing these two seemingly contradictory requirements is no easy task. Therefore, engineers have developed an objective test that matches an oil formulation’s viscosity with something called “High-Temperature High Shear" (HTHS), which is related to the degradation of friction modifiers in oil under high-stress conditions. Put differently, this means that the polymeric friction modifiers in oil degrade, or are broken up in high shear conditions such as in the interfaces between piston rings and cylinder walls, crankshaft bearing journals, and some valve train components.
In practical terms, this means that when the friction modifiers are broken up the oil “thins out” in a process that is largely independent of the oil’s temperature. Note though, that this should not be confused with the “normal thinning out” of oil caused by temperature, which is merely a case of the high temperature pushing the various constituent molecules of the oil a bit further apart, thus “loosening” the molecular structure of the oil.
So, in the context of an oil formulation's High-Temperature High Shear rating, the word "shear' refers to the resistance the viscosity modifiers in the oil have to being shorn apart at high temperatures in high-stress conditions. Note that HTHS viscosity is typically expressed in centiPoise (cP), but it is sometimes also expressed as MilliPascal per second in some GF-6 specifications. Note that one MilliPascal per second is equal to one centiPoise (cP).
We need not delve into the complexities of how HTHS ratings are measured and verified here, but suffice to say that several studies and research programs conducted by organizations that are not connected to the oil industry have shown an unambiguous relationship between GF-6 oil formulation’s HTHS ratings and measurable improvements in fuel economy. For example, fuel economy generally improves by between 0.5 per cent and as much as 2.0 per cent for each 0.5 cP reduction in HTHS viscosity, depending on the engine type and operating conditions. In other words, the thinner the oil is, the easier it flows through the engine, and the less fuel the engine uses, which brings us to-
The biggest downside of low HTHS oil formulations is that inappropriately low HTHS oil can affect the durability of some older engines because even a marginal decrease in oil film thickness can cause boundary lubrication conditions and increased mechanical wear. Moreover, using inappropriate oil could also cause serious decreases in oil pressure at low engine speeds, such as during idling when the engine is hot.
Worse, though, high-stress conditions could cause the permanent loss of viscosity due to polymeric fiction modifiers being torn apart, which does not only thin out the oil to unacceptable levels, but also largely renders the friction modifiers useless because these particular polymers depend on their long chain-like structures remaining intact to be effective.
So, to prevent this type of oil degradation, the GF-6 oil standards and specifications, and particularly the SAE J300 standard, include strictly enforced HTHS limits to ensure that all GF-6 engine oils can be relied on to provide the necessary lubrication and protection under high-temperature high shear conditions in all late-model engines under normal operating conditions.
For instance, for any GF-6 compliant, OEM-approved oil formulation to be classified as a SAE15W40 (or equivalent ACEA (European Automobile Manufacturers’ Association classified grade) viscosity grade, that oil must have a 3.7 cP or higher HTHS viscosity rating. Similarly, the requirement for a GF-6 compliant, OEM-approved oil formulation to be classified as SAE 5W30 (or equivalent ACEA classified grade) is a minimum HTHS viscosity rating of only 2.9 cP.
The two examples above show two things. The first is that the higher an HTHS viscosity rating is, the "thicker" the oil is. The second thing is that the lower an HTHS viscosity rating is, the “thinner” the oil is, but with the proviso that below certain viscosity grades, HTHS ratings have minimum allowable values to ensure these oil formulations provide new engines with adequate lubrication while minimizing pumping losses, at the same time. (Italics and bolding added for emphasis)
From our perspective as mechanics and technicians, the minutiae and highly technical details of HTHS ratings and their relationship to oil viscosity represent a clamouring background noise that could easily distract us from our primary goal, which is not to put the wrong GF-6 oil in the wrong engine. As a practical matter, some GF-6 formulations should never be used in engines that date from before 2017, but the good news is that all major oil formulators have gone to some pains to mark their packaging clearly to prevent the inappropriate use of the latest oil formulations. Before we get to the details of how GF-6 compliant oil is classified, though, we need to discuss-
Many online resources that discuss the details of GF-6 oils use a plethora of abbreviations for industry players, regulatory bodies, and other organizations and corporate entities that are involved in oil marketing and distribution.
This can be extremely confusing and even more so when not all correspondents use all known abbreviations. One good case in point is the fact that while some technical resources use the abbreviation ILSAC (International Lubricants Standardization and Approval Committee) in an off-hand way or sometimes not at all, others use it so often that it creates the impression that ILSAC was the driving force behind the development of the GF-6 oil standard.
The truth of the matter lies elsewhere. The fact is that ILSAC was formed by AAMA (American Automobile Manufacturers Association), DaimlerChrysler Corporation, Ford Motor Company, General Motors Corporation, and JAMA (Japan Automobile Manufacturers Association) as long ago as 1992. The stated purpose of this organization was to define, regularise, and standardise minimum performance standards for passenger car engine oil formulations used in the petrol engines these carmakers produced at the time.
ILSAC also developed a system known as EOLCS (Engine Oil Licensing and Certification System) to administer the licensing requirements of oil formulations. However, this system was based on then-existing API (American Petroleum Institute), SAE International, and ASTM International test standards and procedures.
So why is any of this important? It is important simply because it is extremely easy to fall down a rabbit hole filled with oil industry abbreviations, acronyms, and other paraphernalia that could easily distract us from making the most appropriate decisions when it comes to selecting oil for our customers' vehicles. We could, of course, consult their vehicle's manuals, or contact a dealership to get the details on the required oil, or we could launch an online search, but a more profitable approach would be to forget the dozens of abbreviations and acronyms and concentrate on the details printed on oil containers, which brings us to-
Unless one works in the lubrication industry at an advanced level, it is easy to become distracted by the minutiae of the latest oil standards, so one way to approach the problem is to reduce it to its simplest form. In this case, the simplest form is the fact that the GF-6 standard has only two categories, these being GF-6A and GF-6B. Let us look at these categories in turn, starting with-
GF-6A
Introduced in May 2020, GF-6A formulations are designed to provide prescribed minimum levels of -
While this list of properties is clear enough, the problem is that a) these are the minimum requirements, and b), that some engines may require two or more of the listed requirements, which makes it crucially important to consult reliable, OEM-level service information when selecting any GF-6 compliant oil for any vehicle that is less than six years old.
GF-6B
Also introduced in May 2020, GF-6B specifications only apply to oil formulations with the SAE 0W-16 viscosity grade. It should be noted though that few, if any engines made before 2020 are designed to run on GF-6B oil, which, at room temperature, has about the same viscosity as cream.
Note also that GF-6B oil must have all of the performance properties and characteristics of GF-6A oil formulations, except for the same viscosity.
Selecting the appropriate oil for vehicles that are older than about 10 to 12 years is a bit easier. Consider the table below, but bear in mind that all previous GF-X oil standards, from GF-5 down to GF-1 are now obsolete, and oil formulations conforming to these standards are no longer available-
|
GF-5 |
Obsolete |
Use GF-6A where GF-5 is recommended |
|
GF-4 |
Obsolete |
Use GF-5 where GF-4 is recommended |
|
GF-3 |
Obsolete |
Use GF-5 where GF-3 is recommended |
|
GF-2 |
Obsolete |
Use GF-5 where GF-2 is recommended |
|
GF-1 |
Obsolete |
Use GF-5 where GF-1 is recommended |
Although the above information is accurate, it is not enough to avoid making mistakes when selecting oil for any given vehicle because oil classifications and oil category designations are different based on where the oil was made. For instance, API designations are simple two-digit combinations that describe the application of a particular oil formulation, while ILSAC designations are based on oil standards, such as GF-6, GF-5, and so on.
At first glance, this difference can be confusing, but the good news is that although API and ILSAC designations are different, the actual oil formulations are exact equivalents of each other. Consider the table below that compares the two classification systems-
|
API Spec |
ILSAC Spec |
Intended Application |
|
SP |
GF-6B |
Applies only to engines requiring SAE0W-16 oil |
|
SN-Plus |
GF-6A |
Use in all GDI engines, and small engines with forced induction |
|
SN |
GF-5 |
Introduced in 2010 for use in high-output turbo engines |
|
SM |
GF-4 |
Use in engines made between 2010 and 2004 |
|
SL |
GF-3 |
Use in engines made between 2004 and 1996 to 2001 |
|
SJ |
GF-2 |
Use in engines made between 1996 and 2001 |
|
SH |
GF-1 |
Use in engines made between 1996 and 1988* |
|
SA-SH |
-------------- |
Obsolete in both classification schemes |
* Not suitable for use in engines made before 1988.
Note that each category in the above table has a different viscosity and performance characteristics that may or may not suit a particular vehicle under tough or demanding operating conditions. Nonetheless, the broad categories as outlined above should suffice to point you in the right direction in terms of avoiding wildly inappropriate choices when you have to select oil to suit tough operating conditions.
However, if you are not fully conversant with new oil standards and specifications, making the most appropriate choice(s) can become a lot more difficult when you also have to consider a third classification scheme, that covers European-made vehicles, so let us look at the-
The oil classification scheme devised by ACEA (European Automobile Manufacturers’ Association) is considerably more complicated and convoluted than either the ILSAC or API schemes, but the upside is that the law in the EU prohibits the use of vague or ambiguous language on product packaging. Thus, as a practical matter, this means that the application of ACEA-classified oil formulations is spelled out clearly, which greatly reduces the possibility of inadvertently using the wrong oil in a European-made vehicle.
With that said, let us look at ACEA oil classifications in some detail. Let us start with-
A1/B1
This category was made obsolete when the 2016 ACEA classifications (aka Sequences) were introduced. This oil category was roughly equivalent to the now obsolete API SA-SH category.
A3/B3
This category consists of a range of low viscosity oils that are suitable for use in harsh or demanding operating conditions- depending on how the vehicle manufacturer defines “harsh or demanding”. This category of oil is also suitable for use in engines with long oil change intervals.
A3/B4
This category is suitable for use in most petrol light vehicles, as well as in light commercial vehicles with direct injection diesel engines. This category of oil can also be used in most, if not all petrol and diesel light vehicles that require A3/B3 oils.
A5/B5
While this category is not exactly equivalent to the ILSAC GF-6B or API SP categories, it is sufficiently similar to limit its use to European engines made after 2019 because most post-2019 European engines require oil with an HTHS (High-Temperature High Shear) viscosity rating of between 2.9 MilliPascal per second and 3.5 MilliPascal per second.
Put differently, this means that European engines made after 2019 typically require low viscosity, low SAPS oils that are unsuitable for use in vehicles that are older than four years because A5/B5 oils cannot provide adequate lubrication in engines that are older than 4 to 5 years.
The above should suffice to describe ACEA oil classifications for petrol and diesel engines in general terms, but there is another category of ACEA-classified oils that deserves a special mention, so let us look at ACEA C-class oils, these being-
Even though many European-made diesel light vehicles emit fewer harmful exhaust emissions than some directly comparable petrol vehicles, European car manufacturers are coming under increasing pressure from European governments to make their diesel engines cleaner. As one result of this pressure, car manufacturers and oil formulators have developed a range of ultra-low SAPS oils that are designed specifically for use in diesel vehicles with DPF devices and other advanced exhaust after-treatment systems.
Here are some details of ACEA C-class oil formulations-
C1 oils
These oil formulations have the lowest SAPS ratings, which means that C1 oils are fully compatible with the catalytic materials in all modern diesel exhaust after-treatment systems. Note that C1 oils are intended for use in high-performance direct injection diesel engines in passenger and light commercial vehicles that require an oil with a minimum HTHS viscosity rating of 2.9 MilliPascal per second. Therefore, C1 oil formulations should NOT be used in engines that require oils with higher HTHS viscosity ratings.
C2 oils
C2 oils have mid-level SAPS ratings but are still considered to be compatible with exhaust after-treatment catalytic materials, even at extended oil change intervals.
C3 oils
C3 oils are also mid-SAPS level oils, but the main difference between C2 & C3 engine oils is that C3 oils are designed to be suitable for use in engines that require oil with a minimum HTHS viscosity rating of 3.5 MilliPascal per second.
C4 oils
C4 oils are catalyst-compatible oils that are designed primarily for use in engines with extended oil change intervals. Note that C4 oils have a minimum HTHS viscosity rating of 3.5 MilliPascal per second, which makes these oils unsuitable for use in most late-model diesel engines because it is too “thick”.
C5 oils
C5 oils are roughly equivalent to the ILSAC GF-6B and API SP categories and are intended for use in late-model diesel engines that require oils with a minimum HTHS viscosity rating only of 2.6 MilliPascal per second. In other words, C5 oils should not be used in diesel engines that are older than 3 to 4 years.
We hope that this article has given you some new insights into the complexities of the GF-6 oil standards and specifications as these apply to light vehicles. More to the point, though, we hope that this article has sufficiently demonstrated the dangers of making inappropriate choices when selecting oil for a customer’s vehicle.
So, we would suggest that the safest way of navigating the new oil standard is a) never to guess which oil formulation to use in any given vehicle, and b) to always refer to the vehicle’s manual or other reliable service information to ensure that you always use the right oil for the right vehicle.
