Ford WSS-M2C913-D, 948-B, 950-A: how do you read Ford approvals?

The service book of a diesel Focus says “WSS-M2C950-A”, and the shelf holds a can of 5W-30 marked “Ford WSS-M2C913-D”. The salesman does not hesitate: “That’s Ford oil, and it’s got a D on it, so it’s the latest.” It sounds convincing, and plenty of Ford owners buy their oil exactly that way. But 913-D and 950-A are not two revisions of one approval — they are two different oils for two different engines.

Ford codes have come up on this site before. The article on oil for cars from the USA explained that American 5W-20 and 0W-20 oils have codes of their own and that a code is read together with its suffix. The article on the timing belt in oil covered the 948-B approval, which Ford introduced for the 1.0 EcoBoost. Here we look at the codes themselves, the ones that turn up most often on cans.

How to read a WSS-M2C code

WSS-M2C with a number is a Ford material specification, that is, a requirement for one particular oil: “Ford Material Specification” is exactly how these codes are labelled in the data sheets of Motorcraft oils, Ford’s own brand. I have not found an explanation of the prefix letters in Ford’s documents, and you do not need it to choose an oil. Two things matter.

The number after M2C is a separate specification with its own viscosity, its own ash content and its own range of engines. M2C also appears in the codes of gear oils, automatic transmission fluids and even air-conditioning compressor oil, so “something with M2C” tells you nothing on its own. It is like a part number in a catalogue: change one digit and it is a different part.

The letter, or letter plus digit, after the hyphen is a revision of the same specification. As a rule a newer revision replaces an older one: an oil approved to 913-D is, according to oil data sheets, fine wherever 913-A, 913-B or 913-C was required. But a new letter on its own says nothing about a different number. One number replaces another only where it is stated outright, and always with exceptions: 948-B, for example, covers most petrol engines that used 913-A, B, C or 925, but not the engines that need 913-D. 948-B is not a “successor” to 913-D, it is a neighbour with a different viscosity.

European codes: what stands behind each

I have not found the Ford specifications themselves publicly available, so what follows is what oil makers write about each code in their technical data sheets. Engines are named only where the data sheets name them outright.

There are rarer codes too. 931-E1 is a 5W-50 that Ford recommends for the Ford GT, Focus RS, “hot” Mustangs and the F-150 Raptor R. What lies behind 953-A1 or 957-A1 I could not verify from documents, so for those go by your car’s own documentation.

Why 913-D, 948-B and 950-A are not interchangeable

Look at the table once more: “neighbouring” codes differ in almost everything.

1. Viscosity and HTHS. 913-D is a 5W-30 based on ACEA A5/B5, that is, with a high-temperature high-shear viscosity (HTHS) of 2.9 to 3.5 mPa·s (in plain words, the thickness of the oil film in the most heavily loaded parts of a hot engine). Oils for 948-B are 5W-20 of class C5 with HTHS from 2.6 to 2.9, while 917-A and 937-A call for at least 3.5. Pouring 5W-20 into an engine for which Ford wrote 5W-40 changes the viscosity in a way the designers never intended. These limits are covered in more detail in the article on the current ACEA classes.

2. Ash content. A5/B5, on which 913-D is based, is a full-ash class (sulphated ash up to 1.6%), while C2, C5 and C6 limit ash to 0.8%. For its new diesels with a particulate filter Ford based 950-A specifically on C2, and that matters: ash that does not burn off when the filter regenerates gradually clogs it. Whether 913-D can go into your diesel is decided not by the salesman but by the entry in the documentation.

3. Exceptions to “covers”. Even 948-B, which covers the old 913-A, B, C and 925, is, according to oil data sheets, not suitable for the second-generation Ka (which takes 917-A), for the Focus RS (937-A) or for some Duratec 1.3, 1.6 and 1.8 engines that need 913-D. “Covers the old codes” always means “covers them, apart from the listed exceptions”.

4. A belt in oil. 948-B was created for the 1.0 EcoBoost, whose timing belt runs in oil, and the requirements for 954-A1, according to the oil maker, specifically stress compatibility with such a belt. An oil to 954-A1, according to the same source, is fine where 948-B was required, but not the other way round: an oil labelled “948-B” does not become a 954-A1 oil.

So a bigger number does not mean “newer and better”: Ford wrote each number for its own range of engines, and you cannot swap one for another just “because it’s newer”.

American codes: 945, 946, 947 and beyond

For cars of the North American market Ford writes a separate series of passenger-car codes, and each of these numbers is tied to one viscosity. 5W-20 is 945-A, 945-B1, 960-A1 and 970-A1; 5W-30 is 929-A, 946-A, 946-B1, 961-A1 and 971-A1; 0W-20 is 947-A, 947-B1, 962-A1 and 972-A1. Motorcraft oils carrying 960-A1 and 962-A1 were ILSAC GF-6, while the current ones, carrying 970-A1, 971-A1 and 972-A1, are GF-7A and API SQ.

On shelves in Europe these codes often sit on European 0W-20 oils of class C5 or C6 — and almost always as “meets the requirements”, not as an approval. How to find the American requirement and when an ACEA oil can stand in for it is explained in the article on cars from the USA mentioned above. One thing matters here: a European Ford code does not replace an American one, and vice versa, even if the model was sold under the same name in Europe and America.

Big diesels, gearboxes and axles

For pickup and van diesels in North America there is WSS-M2C171-F1 (on shelves mostly 15W-40, 10W-30 or 5W-40). Ford states plainly, in a position statement for its home market, that for the 3.2 and 6.7 diesels, as well as the older 4.5, 6.0, 6.4 and 7.3, it recommends oils to this specification rather than just API CK-4, because in tests some CK-4 oils protected against wear worse than the earlier CJ-4 oils; so Ford added its own requirements to 171-F1 on top of CK-4. This is the rare case where Ford makes a list of oils meeting 171-F1 publicly available.

MERCON, MERCON V, LV and ULV are Ford fluids for automatic transmissions; what a long list of such names on one can means is covered in the article on universal ATF. Codes such as WSD-M2C200-C or WSS-M2C200-D2 appear on oils for manual and dual-clutch gearboxes, and WSP-M2C197-A or WSL-M2C192-A on oils for rear axles; how to read their classes is explained in the article on GL-4 and GL-5 gear oil.

How to check an oil against a Ford code

1. The full code from the service book — number and suffix together. “Ford 5W-30” without a code is only a viscosity.

2. Approved or “meets”. A genuine approval is marked with the words “approved” or “approval”; the same code after “meets”, “suitable for” or “complies with” is the oil maker’s own claim. And those are the majority: among the oils with Ford codes in our catalogue, roughly three out of four have only “meets”. I have not found a public list of approved Ford passenger-car oils like the one Mercedes-Benz keeps, so check the oil’s data sheet on its maker’s website. How to tell these wordings apart is covered in the article on how to check an oil approval.

3. The car’s market. The owner’s manual of the market the car was built for decides: a European Kuga and an American Escape with the same engine may call for different codes.

4. No book — VIN and the dealer. Fords spanning several generations, and especially cars that Ford developed together with other groups (such as the new-generation Transit Connect with 956-A1), are exactly the case where guessing by engine size is not an option.

I will say it again: a Ford code is read only in full — number and suffix — and another number replaces the one specified for your engine only when Ford or the oil’s data sheet says so outright, with a list of exceptions, and not because it is “newer”. And if a salesman assures you that “913-D is the same as 950-A, only with a newer letter”, ask him to show you that in your Ford’s service book.