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Car Engine Oil, A Basic Buying Guide

A Basic Guide to Car Engine Oil and what all the Specs actually mean

A lot of what you need to know when buying an engine oil.

Basic Care Engine Oil Information

When it comes to choosing oil for your car, this information may seem like going back to basics, but we at Opie Oils are constantly surprised by the amount of people who do not understand what is written on a bottle of oil and therefore have no idea of what they are buying or using.

This article should help most car owners as a basic guide, for more detailed information you can always contact us at Opie Oils and will be happy to help you

So, to be blunt about the subject, if a bottle of oil does not contain the following basic information then DO NOT buy it look for something that does!

  1. The purpose for which it is intended (i.e. engine oil, gear oil, ATF etc)
  2. The viscosity (i.e. 10w-40, 5w-30 etc for engine oils and 80w-90, 75w-90 etc for gear oils)
  3. The specifications that it meets (should contain API and/or ACEA ratings)
  4. The OEM Approvals that it carries and the codes (i.e. MB229.5, VW504.00, FORD 913A, BMW LL04 etc

Ignore the marketing blurb on the label, as in many cases meaningless and we will explain later what statements you should treat with some skepticism

So, what does the above information mean and why is it important?

The Purpose

All oils are intended for an application and in general are not interchangeable. You would not for example put an Automatic Transmission Oil or a Gear Oil in your engine! It is important to know what the oils intended purpose is.


Most oils on the shelves today are "Multigrades", which simply means that the oil falls into 2 viscosity grades (i.e. 10w-40 etc)

Multigrades were first developed some 50 years ago to avoid the old routine of using a thin oil in winter and a thicker oil in the summer.

In a 10w-40 for example the 10w bit (W = winter, not weight or watt or anything else for that matter) simply means that the oil must have a certain maximum viscosity/flow at low temperature.

The lower the "W" number the better the oils cold temperature/cold start performance. I.E. 5w is better than 10w etc

The 40 in a 10w-40 simply means that the oil must fall within certain viscosity limits at 100 degC. This is a fixed limit and all oils that end in 40 must achieve these limits.

Once again the lower the number the thinner the oil, a 30 oil is thinner than a 40 oil at 100 degC etc. Your handbook will specify whether a 30, 40 or 50 etc is required.

Shop for car engine oil by grade / viscosity


Specifications are important as these indicate the performance of an oil and whether it has met or passed the latest tests or whether the formulation is effectively obsolete or out of date.

There are two specifications that you should look for on any oil bottle and these are API (American Petroleum Institute) and ACEA (Association des Constructeurs Europeens d’Automobiles) all good oils should contain both of these and an understanding of what they mean is important.

Shop for car engine by your vehicles specification or use our lookup tool to find Oils, Fluids & Parts matched to your specific vehicle

API Specifications

This is the more basic of the two specs as it is split (for passenger cars) into two catagories.

S = Petrol and C = Diesel, most oils carry both petrol (S) and diesel (C) specifications.

Shop for API Spec Car Engine Oils

The following table shows how up to date the specifications the oil are:


SG - Introduced 1989 has much more active dispersant to combat black sludge

SH - Introduced 1993 has same engine tests as SG, but includes phosphorus limit 0.12%, together with control of foam, volatility and shear stability

SJ - Introduced 1996 has the same engine tests as SG/SH, but phosphorus limit 0.10% together with variation on volatility limits

SL - Introduced 2001, all new engine tests reflective of modern engine designs meeting current emissions standard

SM - Introduced November 2004, improved oxidation resistance, deposit protection and wear protection, also better low temperature performance over the life of the oil compared to previous categories


All specifications prior to SL are now obsolete and although suitable for some older vehicles are more than 10 years old and do not provide the same level of performance or protection as the more up to date SL and SM specifications, so if you’ve a recent model, don’t bother


CD - Introduced 1955, international standard for turbo diesel engine oils for many years, uses single cylinder test engine only.

CE - Introduced 1984, improved control of oil consumption, oil thickening, piston deposits and wear, uses additional multi cylinder test engines

CF4 - Introduced 1990, further improvements in control of oil consumption and piston deposits, uses low emission test engine

CF - Introduced 1994, modernised version of CD, reverts to single cylinder low emission test engine. Intended for certain indirect injection engines

CF2 - Introduced 1994, defines effective control of cylinder deposits and ring face scuffing, intended for 2 stroke diesel engines

CG4 - Introduced 1994, development of CF4 giving improved control of piston deposits, wear, oxidation stability and soot entrainment. Uses low sulphur diesel fuel in engine tests

CH4 - Introduced 1998, development of CG4, giving further improvements in control of soot related wear and piston deposits, uses more comprehensive engine test program to include low and high sulphur fuels

CI4 - Introduced 2002, developed to meet 2004 emission standards, may be used where EGR ( exhaust gas recirculation ) systems are fitted and with fuel containing up to 0.5 % sulphur. May be used where API CD, CE, CF4, CG4 and CH4 oils are specified.


All specifications prior to CH4 are now obsolete and although suitable for some older vehicles are more than 10 years old and do not provide the same level of performance or protection as the more up to date CH4 & CI4 specifications

If you want a better more up to date oil specification then look for SL, SM, CH4, CI

ACEA Specifications

This is the European equivalent of API (US) and is more specific in what the performance of the oil actually is. A = Petrol, B = Diesel and C = Catalyst compatible or low SAPS (Sulphated Ash, Phosphorus and Sulphur). These specs are more commonly found on European oils and in many respects are more important than API for European Manufactured cars.

Unlike API the ACEA specs are split into performance/application catagories as follows:

  • A1 Fuel economy petrol
  • A2 Standard performance level (now obsolete)
  • A3 High performance and/or extended drain
  • A3 High performance and/or extended drain
  • A4 Reserved for future use in certain direct injection engines
  • A5 Combines A1 fuel economy with A3 performance
  • B1 Fuel economy diesel
  • B2 Standard performance level (now obsolete)
  • B3 High performance and/or extended drain
  • B4 For direct injection car diesel engines
  • B5 Combines B1 fuel economy with B3/B4 performance
  • B5 Combines B1 fuel economy with B3/B4 performance
  • C1-04 Petrol and Light duty Diesel engines, based on A5/B5-04 low SAPS, two way catalyst compatible
  • C2-04 Petrol and light duty Diesel engines, based on A5/B5-04 mid SAPS, two way catalyst compatible.
  • C3-04 Petrol and light duty Diesel engines, based on A5/B5-04 mid SAPS, two way catalyst compatible, higher performance levels due to higher HTHS

Note: SAPS = Sulphated Ash, Phosphorous and Sulphur.

Put simply, A3/B3, A5/B5 and C3 oils are the better quality, stay in grade performance oils.


Many oils mention various Car Manufacturers on the bottle, the most common in the UK being VW, MB, BMW, Ford or Vauxhall but do not be misled into thinking that you are buying top quality oil because of this

Oil Companies send their oils to OEM’s for approval however some older specs are easily achieved and can be done so with the cheapest of mineral oils. Newer specifications are always more up to date and better quality/performance than the older ones

Some of the older OEM specifications are listed here and depending on the performance level of your car are best ignored if you are looking for a quality high performance oil:

VW - 500.00, 501.00 and 505.0

Later specs like 503.00, 503.01, 506.00 are better performing more up to date oils but as far as VW is concerned even these have now been superseded by the more recent VW504.00 and VW507.00 specifications, and the latest VW508.00 and VW509.00 specs.

MB - 229.1, 229.3

Later specs like 229.31, 229.5, and 229.51 are better performing and more up to date oils

BMW - LL98

Later specs like LL01 and the latest LL04 oils are better performing and more up to date. Lower viscosity engine oils for the latest engines need to be approved to the BMW LL12 FE, BMW 14 FE+ or BMW 17 FE+ specifications.

Shop for Car Engine Oils by Car Make Approvals / Specifications


Above is the most accurate guidance we can give without going into too much depth however there is one final piece of advice regarding labelling.

Certain statements are made on labels that are meaningless and just marketing hype; here are a few to avoid!

  • Recommended for use where...............
  • May be used where the following specifications apply...............
  • Approved by.............................(but with no qualification or specification)
  • Recommended/Approved by (some famous person, these endorsements are paid for)
  • Racing/Track formula (but with no supporting evidence)

Also be wary of statements like "synthetic blend" if you are looking for a fully synthetic oil as this will merely be a semi-synthetic.

Like everything in life, you get what you pay for. The cheaper the oil the cheaper the ingredients, lower the performance levels and older the specs it meets so beware!

Shop For Car Engine Oils.