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Car Engine Oil Guide

All the oil information you need in one place

Selecting the correct oil for your vehicle can be a bit of a mine field. Some basic understanding of what the specifications are, and what the numbers printed in the can mean will be a help to selecting the correct oil.


Just about all modern vehicles use a multigrade oil, so what to does it all mean?

If you see an expression such as 10W-40, the oil is a multigrade. This simply means that the oil falls into 2 viscosity grades, in this case 10W & 40. This is made possible by the inclusion of a polymer, a component which slows down the rate of thinning as the oil warms up and slows down the rate of thickening as the oil cools down.

It was first developed some 50 years ago to avoid the routine of using a thinner oil in winter and a thicker oil in summer.

For a 10w-40 to attain the specification target a 10W ( W = winter) the oil must have a certain maximum viscosity at low temperature. The actual viscosity and the temperature vary with the viscosity grade but in all cases the lower the number, the thinner the oil, e.g. a 5W oil is thinner than a 10W oil at temperatures encountered in UK winter conditions. This is important because a thinner oil will circulate faster on cold start, affording better engine protection.

For a 10w-40 to attain the other specification target SAE 40 the oil must fall within certain limits at 100 degC. In this case the temperature target does not vary with the viscosity grade, if there is no "W", the measuring temperature is always 100degC. Again the lower the number the thinner the oil, a 30 oil is thinner than a 40 oil at 100 degC., which is typical of maximum bulk oil temperatures in an operating engine.

The engine makers are, of course, very well aware of this and specify oils according to engine design features, oil pump capacities, manufacturing tolerances, ambient temperature conditions etc. It is important to follow these guidelines, they are important and are an are stipulated for good reasons.

Now we know what the numbers are all about, lets have a look at what specifications there are, and what they mean. Many manufacturers will have their own specification for the oil required for a particular vehicle, these should be listed in the owners manual for the vehicle, BMW for example have the current BMW LL04 spec, for most BMW's post 2004, if the oil is approved to this spec it will be listed on the can.

In addition to manufacturer specifications there are also general specifications. The most popular are ACEA and API, again check the owners manual to find the correct spec for your car.

Here is a list of the specs.

API Specifications

API = American Petroleum Institute

S = Service - Petrol Engine Performance

C = Commercial - Diesel Engine Performance


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 standards

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.

SN – Introduced in October 2010 for 2011 and older vehicles, designed to provide improved high temperature deposit protection for pistons and turbochargers, more stringent sludge control, improved fuel economy, enhanced emission control system compatibility, seal compatibility, and protection of engines operating on ethanol-containing fuels up to E85.


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

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.

CJ-4 – Introduced in 2010 exhaust emission standards. These oils are formulated for use in all applications with diesel fuels ranging in sulphur content up to 500 ppm (0.05% by weight). However, the use if these oils with greater than 15 ppm (0.0015% by weight) sulphur fuel may impact exhaust after treatment system durability where particulate filters and other advanced after treatment systems are used. Optimum protection is provided for control of catalyst poisoning, particulate filter blocking, engine wear, piston deposits, low and high temperature stability, soot handling properties, oxidative thickening, foaming, and viscosity loss due to shear.

ACEA Specifications

ACEA (European Automobile Manufacturers Association) have a system of rating oils, which you will find on the container of almost every oil on the market. These are the current specifications, previously oils were given separate petrol and diesel ratings, but from November 2004 onwards, those have been combined (A still refers to Petrol and B to Diesel engines).

A1/B1 Category for Fuel Economy engine oils with especially low High Temperature High Shear viscosity. HTHS of 2.6 to 3.5 mPas applies to XW-20, 2.9 to 3.5 mPas for all others. Corresponds to the old A1 and B1 specifications with some new engine tests.

A2/B2 Basic requirements.Will be replaced by the GLOBAL DLD-1 specification.

A3/B3 Category for high-performance and Fuel Economy engine oils. Exceeds ACEA A1/B1 with regard to Noack (evaporation losses), piston cleanliness and oxidation stability.Extended oil change intervals possible.

A3/B4 Same as A3/B3 but also for direct injection diesel engines.

A5/B5 Category for high-performance engine oils. For TDI engines with Fuel Economy Performance. In addition with lowered HTHS (2.9 to 3.5). Extended oil change intervals possible.

LOW SAPS Diesel Engines

An additional category appears in these specifications in which sulphate ash, phosphorous and sulphur content (SAPS) is limited.

C1 Largely based on the ACEA A5/B5. Strict limitation of SAPS content.Low HTHS viscosity of >2.9 mPas.

C2 Same as C1 but with somewhat higher SAPS content permissible (as with C3).

C3 Same as C2 except for HTHS > 3.5 and without Fuel Economy performance.

C4 Same SAPS content as C3, HTHS viscosity as C1.

As we said at the beginning, selecting the correct oil for your vehicle can be a bit of a mine field. This is where we can help, simply call us on 01209 202944 or email us at and our friendly team will be happy to help.