Oil Specifications

Millers Oils logo By Martyn Mann, Technical Director for Millers Oils



For many years engine oils have been specified by two main bodies, the first one being API (The American Petroleum Institute) and  ACEA (Association des Constructeurs Europeens d’Automobiles)

The API system uses S and C ratings for “spark” and “compression” respectively for petrol and diesel oils followed by a second letter denoting how far up the sequence the specification has evolved. For example these specifications date back over 80 years but started with SA and CA specification products. Today the specs have reached SN and CJ with newer ones imminent.

The ACEA system uses A’s, B’s and C’s for their classification. A specs are for passenger cars with petrol, B specs are for passenger cars with diesel  and C specifications are for either petrol or diesel, but with the fitment of after treatment devices such as catalytic convertors and diesel particulate filters and is essentially a chemical limitation on (S)ulphated0 (A)sh content, (S)ulphur and (P)hosphorus (known as low SAPS). This is necessary as normal oils can either block DPFs or poison the  catalytic convertors if used for long periods.

If we examine the intricacies of either API or ACEA specifications, there is usually a long list of engine tests involved which measures an oils ability to keep various engine components free from carbon build up, create low levels of deposits on valve heads, keep piston ring grooves clean, do not give excessive varnishing, provide expected economy etc etc. The list is extensive and usually goes on for pages.

A typical oil specification from the 1970’s might look like this API SF, CD together with the other essential bit of information 15w40, the viscosity. Move forward 40 years and it could look like this API SN, ACEA A3, B4 5w30 or API SN, ACEA C2 5w30 for an oil with a DPF fitted.

Most recently nearly all the vehicle OEMs have taken a basic API or ACEA structure and used it to produce their own specification which might have extra fuel economy as part of the test regime, or lower levels of oil consumption for example.

Jaguar adopted a set of Ford specifications for their lubricants for a while, but have recently produced their own, which look like this:


JLR Standard  Ford Standard Viscosity Grade
STJLR.03.5003 WSS-M2C913-D 5W-30
STJLR.03.5004 WSS-M2C925-B 5W-20
STJLR.03.5005 WSS-M2C934-B 5W-30
STJLR.03.5007 WSS-M2C950-A 0W-30
STJLR.51.5122 None 0W-20


The important thing when selecting your oil is to get the correct specification AND viscosity which will deliver the protection for the engine BUT also the Cat/DPF and the correct economy that the vehicle was designed for. My own personal preference is to not mix oils with other manufacturers’ products, however by ensuring that the specifications on the packaging are the same, emergency top-ups are least likely to cause issues.


See also:

Oil Grades


To follow …..

February 2017 issue: Recommended Engine Oil (grade and specification) for all Jaguar Cars.



Millers Oils

All information correct at time of publishing

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