Search Button


Account Button


Basket Button

Basket Basket

Search Suggestions



View All Results


Find Oils & Parts

Select Your Motorcycle:

Manually Enter
Modified Vehicles

Car Engine Oil Guide

Selecting the correct oil for your vehicle can be a bit of a minefield. 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. What 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 oil specifications defined by the industry bodies API and ACEA

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. Now considered obsolete, and not suitable for most petrol engines built after 1993.

SH - Introduced 1993 has same engine tests as SG, but includes phosphorus limit 0.12%, together with control of foam, volatility and shear stability. Now considered obsolete, and not suitable for most petrol engines built after 1996.

SJ - Introduced 1996 has the same engine tests as SG/SH, but phosphorus limit 0.10% together with variation on volatility limits. Not recommended for vehicles built after 2001; use one of the petrol specifications below.

SL - Introduced 2001, all new engine tests reflective of modern engine designs meeting current emissions standards. Not recommended for vehicles built after 2004; use one of the petrol specifications below.

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. Not recommended for vehicles built after 2010; use one of the petrol specifications below.

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. Not recommended for vehicles built after 2020; use one of the petrol specifications below.

SP - Introduced in May 2020 to try and tackle the problem of low-speed pre-ignition (LSPI), and provide timing chain wear protection, improved high temperature deposit protection for pistons and turbochargers, and more stringent sludge and varnish control. API SP with Resource Conserving is a "sub-category" of API SP, matching ILSAC GF-6A by combining API SP performance with improved fuel economy, emission control system protection 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.

CJ4 – Introduced in 2017, developed to meet new exhaust emission standards. 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.

CK4 Introduced in 2010 to meet enhanced exhaust emission standards. These oils are particularly effective at sustaining emission control system durability where particulate filters and other advanced aftertreatment systems are used. API CK-4 oils are designed to provide enhanced protection against oil oxidation, viscosity loss due to shear, and oil aeration as well as protection against catalyst poisoning, particulate filter blocking, engine wear, piston deposits, degradation of low- and high-temperature properties, and soot-related viscosity increase.

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.

A7/B7 engine oil offers increased protection against timing chain wear, turbocharger compressor deposits, and LSPI (Low Speed Pre-Ignition) issues. These are critical factors that can lead to engine damage if not addressed properly.

LOW SAPS Diesel Engines

An additional category appears in these specifications in which sulphate ash, phosphorous and sulphur content (SAPS) is limited. This is to provide compatibility with exhaust aftertreatment systems such as diesel particulate filters.

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.

C5 engine oils will be mid-SAPS with a HTHS viscosity between 2.6 and 2.9 mPa*s. Fuel economy-wise C5 demands 2% better fuel economy than C3.

ACEA C6 is largely based on ACEA C5, but also introduces new tests and thus provides better low speed pre-ignition protection (LSPI protection) than C5 oils.

As we said at the beginning, selecting the correct oil for your vehicle can be a bit of a minefield. Get our engine oil recommendation by entering your vehicle registration at the top of this page for an instant list of suitable products. Or call us on 01209 202944 / email us at and our friendly team will be happy to help.