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which engine oil?

Helping you choose the right oil for your engine

viscosity and specification explained

Engine oils aren’t all the same so if you need to top-up, you'll need to make sure you use the right grade and specification.

Don’t assume you can use the same oil you used for your last car.

Do I still have to check the oil level?

Actually, it's never been more important to check your engine's oil level regularly.

  • Try to do it every couple of weeks and before any long journey
  • Extended service intervals, smaller capacity sumps, turbo chargers and thinner, synthetic oils can all add up to higher oil usage.
  • A drop in oil level can do more damage in a modern engine with a smaller sump – oil spends less 'recovery time' in the sump cooling down and hotter oil will breakdown and oxidise more rapidly leading to increased wear.

Engine oil

Engine oil 'grade' (viscosity)

Oils are graded according to their viscosity – basically how thick or thin they are.

Viscosity changes with temperature, so engine oils are 'multi-grade' to cope with a wide range of operating temperatures – additives (viscosity improvers) are used to give the oil one viscosity when cold and another when hot.

Both grades will be marked on the container e.g. 5W–30. The first is the cold temperature grade, and the second the high temperature grade.

Your car handbook will tell you the grade(s) to be used.

Oil specifications

All engines are not the same, so it shouldn't be a surprise that oils are not the same either.

Modern car engines need oils that are really durable, and last for thousands of miles between services.

Modern oils protect against corrosion and sludge formation, and contain detergent additives to keep the engine clean.

Car manufacturers and oil companies work together to agree performance specifications for engine oils. There are several different sets of standards around the world:

  • The American Petroleum Institute (API)
  • The European Constructors (CCMC/ACEA)
  • The International Lubricant Standardization and Approval Committee (ILSAC), or
  • The Japanese Automotive Standards Organization JATO.

Later specification oils are usually, but not always, suitable for older cars, while older specification oils shouldn’t be used in newer cars.

Manufacturer's specifications

Many car manufacturers develop their own engine oil specifications, most notably Volkswagen and Mercedes-Benz, but also BMW, GM, Porsche, PSA and others.

These are increasingly very specialised 'long life' oils needed to support very long service intervals. 

Check your handbook

Your handbook will list the specification(s) and grades of engine oil that are suitable.

  • Where the handbook quotes the manufacturer's own specification you must look for this on the oil container.
  • They may also give an acceptable equivalent ACEA or API specification as well, though this might be for 'emergency top-up only'.
  • If you're struggling to find the right oil, try the parts department of a manufacturer's dealer.
CCMC/ACEA (European Constructors) Specifications

Here’s an example of ACEA specifications to show the range of oils available:

Petrol
  • A1 Fuel economy petrol
  • A2 Standard performance level
  • A3 High performance and/or extended drain
  • A5 Fuel economy petrol with extended drain capability
Diesel
  • B1 Fuel economy diesel
  • B2 Standard performance level
  • B3 High performance and/or extended drain
  • B4 For direct injection passenger car diesel engines
  • B5 Fuel economy diesel with extended drain capability
  • E1 Non-turbo charged light duty diesel
  • E2 Standard performance level
  • E3 High performance and extended drain
  • E5 High performance and extended drain including some API specs
  • E6 Euro I to VI engines –with EGR, with or without DPF and engines with SCR NOx reduction
  • E7 Euro I to V engines – most EGR  and most SCR NOx engines but without DPF
  • E9 Euro I to VI – with or without DPF, most EGR and most with SCR NOx reduction
Diesel with diesel particulate filter (DPF)

If you have a diesel car fitted with a DPF you must use one of the latest 'low SAPS' (Sulphated Ash, Phosphorous, Sulphur) oils.

Using 'normal' oil instead of low SAPS can result in blocking of the DPF.

  • C1 Low SAPS (0.5% ash) fuel efficient
  • C2 Mid SAPS (0.8% ash) fuel efficient, performance
  • C3 Mid SAPS (0.8% ash)
11 May 2017

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