What engine oil quality classifications are there?

Section API classification, article 4 of 41 108 words, 7 minutes

In this section: 4 articles
  1. API Engine Oil Classification
  2. Decoding the API code
  3. What API classes are there?
  4. What engine oil quality classifications are there?

In many cases, what a carmaker requires of an engine oil comes down first and foremost to meeting the international quality classifications. There are four main ones, and each follows its own logic, so it’s worth taking a quick look at how they differ and which classes apply today.

  1. API is the American engine oil classification system (more in the article the API engine oil classification). Classes for petrol engines start with the letter S, those for diesels with the letter C. The idea behind API is that every new quality class sets stricter requirements than the ones before and, as a rule, replaces all of them. So if the maker of your car asks for an API SL oil (and has no other requirements), you can usually also use oils certified to API SM and later classes. And there have been quite a few later classes since then: API SN (2010); the API SN Plus supplement (2018), which adds protection against low-speed pre-ignition (LSPI) in turbocharged direct-injection engines; API SP (2020), which on top of that brought timing chain wear protection and tougher limits on piston and turbocharger deposits; and finally API SQ (2025). If the can shows the words Resource Conserving next to the class, the oil has also proved its fuel economy and its protection of the exhaust after-treatment system; in effect, these are the requirements of the matching ILSAC class (more on that below). On the whole, API is a more or less universal classification, and for choosing an oil for an engine built for the European market it is usually not enough on its own. The API diesel line works the same way: CI-4 and CI-4 Plus (2002 and 2004), then CJ-4 (2006), the first class for engines with particulate filters, with limits on ash, sulphur and phosphorus, and CK-4 (2016), which replaces them all. FA-4, however, which appeared at the same time, stands apart: these are oils with a reduced high-temperature viscosity (HTHS 2.9–3.2 mPa·s) for certain fuel-efficient heavy-duty diesels built in 2017 or later, and they do not replace the earlier classes: never put such an oil into a diesel that was not designed for FA-4. In any case, the primary source of information on the oil quality you need is only the service book of your particular car or its owner’s manual.

  2. ACEA is the European engine oil quality classification (its history and what the classes mean are covered in separate articles). In 1996, when it appeared, the logic behind approving new classes was not much different from the American one. But the modern ACEA classes take engine design into account more and more, and the set of classes itself is revised regularly: each edition is labelled with a year, outdated classes are dropped and new ones are added. The A1/B1 class, for example, is no longer part of the classification. In the 2021 edition, three “A/B” classes remain for passenger cars: A3/B4 (high-temperature viscosity HTHS of at least 3.5 mPa·s, for powerful and hard-working engines), A5/B5 (HTHS 2.9–3.5 mPa·s, for fuel economy) and the new A7/B7 (like A5/B5, plus protection against LSPI and turbocharger deposits). Cars with particulate filters and catalytic converters get the C series: oils with limited sulphated ash, phosphorus and sulphur, namely C2, C3, C4, C5 and the new C6. Heavy-duty diesels have a separate E series (in the 2022 edition, for example, E4, E6, E7, E8 and E11). Here “newer” does not mean “better” at all: C5 or C6 allows a lower high-temperature viscosity than C3, so such an oil is no good for an engine that calls for C3. Different requirements do not mean higher or lower ones: oils of these classes are simply meant for engines of different design. Even so, ACEA is still a more or less universal classification, and many carmakers, on top of compliance with some ACEA class, set their own requirements for the oil as well: approvals.

  3. ILSAC is the “International Lubricant Standardization and Approval Committee” for passenger-car petrol engines, set up by the American (AAMA) and Japanese (JAMA) carmakers’ associations. In essence, the ILSAC classes are refined API requirements with the emphasis on fuel economy: ILSAC GF-5 (2010) corresponds to API SN with the Resource Conserving mark, and ILSAC GF-6 (2020) to API SP with the same mark. They are developed the same way the Americans do it: a newer class means stricter requirements, and engines that call for an earlier class will, as a rule, accept oils certified to a later one. But since 2020 there has been an exception here too: GF-6 is split into GF-6A, for familiar viscosities such as 0W-20 or 5W-30, which replaces the earlier classes, and GF-6B, only for very thin 0W-16 oils that may be used only in engines designed for them. Telling them apart is easy: GF-6A carries the familiar ILSAC “starburst” mark on the can, GF-6B a shield-shaped mark. ILSAC GF-7, released in 2025, is split on the same principle into GF-7A and GF-7B.

  4. JASO is the Japanese engine oil quality classification. Today it is best known for its motorcycle oil classes. Four-stroke motorcycle engines whose clutch runs in the oil bath get the JASO MA, MA1 and MA2 classes (MA2 sets higher requirements for friction properties), while scooters with a CVT and a dry clutch get JASO MB, a reduced-friction oil. Do not mix them up: an MB oil in an engine with a “wet” clutch can make the clutch slip. For two-stroke engines JASO has the FB, FC and FD classes, and for diesels DL-1 (passenger cars) and DH-1, DH-2 (heavy duty).

How does all this relate to approvals? A carmaker usually takes some API, ACEA or ILSAC class as the basis and adds its own tests to it: that is how, for example, the Mercedes-Benz approvals and the Volkswagen ones work, or General Motors’ dexos standards. That is why an approval always “outranks” a class: an oil with the approval also meets the base class, while an oil with a suitable class may well have no approval.

The main thing that follows from this comparison: in API and ILSAC a new class, as a rule, replaces the old one (the exceptions are API FA-4 and ILSAC GF-6B and GF-7B, which are designed for special engines), while in ACEA different classes are oils for different engines, and a “newer” class will not necessarily suit your engine. So choose your oil not by the latest code on the can, but by what the maker of your car requires: by class and, if one is specified, by approval.