Walk into a motor factors and there are forty bottles that all say "fully synthetic 5W-30". Only some of them are right for your car. This guide explains what the labels mean and how to be sure you are buying the correct oil, because using the wrong one is one of the most common and most costly DIY servicing mistakes.
The viscosity grade: 5W-30, 0W-20 and friends
The number before the W (for winter) tells you how easily the oil flows when cold; the lower it is, the quicker it reaches the top of the engine on a frosty start. The second number tells you how thick it stays at operating temperature. 5W-30 is the most common grade in the UK, but many newer engines specify 0W-20 or 0W-30, and some older ones 10W-40. Your handbook and the oil filler cap will usually state the grade.
The ACEA class: why two 5W-30s are not the same
The European standard ACEA splits oils into families:
- A3/B4: traditional high-performance oil for petrol and diesel engines without a particulate filter.
- C2, C3, C5, C6: "low SAPS" oils with reduced ash, which are essential for engines fitted with a diesel particulate filter (DPF) or petrol particulate filter (GPF). The wrong oil slowly blocks the filter.
- A5/B5, A7/B7: fuel-economy oils for engines designed for thinner lubrication.
A 5W-30 A3/B4 and a 5W-30 C3 look identical on the shelf and are not interchangeable.
Manufacturer approvals: the part that really matters
Most car makers publish their own oil specification and this is the one to match. Examples you will see on bottles:
- VW 504 00 / 507 00 for most VW, Audi, SEAT and Skoda engines (VW 502 00 / 505 01 for older ones)
- BMW Longlife-04 and Longlife-01
- MB 229.51 / 229.52 for Mercedes
- Ford WSS-M2C913-D (5W-30) and WSS-M2C948-B (5W-20 EcoBoost engines)
- PSA B71 2290 / 2312 for Peugeot, Citroën and Vauxhall engines of PSA design
- GM dexos2 for older Vauxhall engines, Renault RN0700 / RN0710 / RN17, Fiat 9.55535 and so on
If the bottle carries your manufacturer's approval it will also be the correct grade and ACEA class, so the approval is the simplest thing to check.
Fully synthetic, semi-synthetic or mineral?
Any engine built in the last twenty years should have a fully synthetic oil; it holds its viscosity longer, keeps the engine cleaner and copes with turbochargers. Semi-synthetic is acceptable on older cars that specify a 10W-40 and nothing more exotic. Mineral oil belongs in classic cars. Our article on synthetic versus semi-synthetic oil goes into the differences.
How much oil?
Small petrol engines take around 3.5 to 4.5 litres with a filter change; 2.0-litre diesels typically 4.5 to 6 litres. A 5-litre bottle covers most cars, which is why our Small and Medium kits are sized the way they are. Always fill to the dipstick rather than to the number in the book.
Three ways to be certain
- Check the handbook, usually under "Capacities" or "Fluids".
- Look at the oil filler cap; many list the grade and approval.
- Or just enter your registration on our homepage. We match the oil to your engine from the DVLA record and check it again before dispatch, so you never need to decode a label.
Get the right parts for your car
Enter your registration at easyservicekits.com and we will match the correct oil grade, quantity and filters to your exact engine, check them before dispatch and deliver free anywhere in the UK. Not sure which kit you need? Email hello@easyservicekits.com with your reg and we will tell you.