# What Do Engine Oil Grades and Specifications Mean? | Otto Explains | AutoTronix **Section:** Otto Explains **Canonical:** https://autotronix.om/otto/engine-oil-types-explained **Language:** English **Arabic version:** https://autotronix.om/ar/otto/engine-oil-types-explained --- ## Short Answer An engine oil's grade, such as 5W-30, describes its viscosity: the part with the W covers how the oil flows when cold, and the number after the dash covers its thickness at operating temperature. Codes such as API SP or SQ and ACEA C3 set a minimum performance level, and a car maker's own approval confirms the oil has been tested for particular engines. The right oil is the one that matches the grade and every specification and approval in your owner's manual. --- ## What do the numbers in a grade such as 5W-30 mean? Viscosity grades come from the SAE J300 standard. The part with a W (for winter) describes the oil's behaviour when cold, measured by cold-cranking and pumping tests: a lower number, such as 0W rather than 10W, flows more readily at [a cold start](https://autotronix.om/otto/warm-up-car-before-driving). The number after the dash is the high-temperature grade, set by the oil's viscosity at 100 °C and a minimum high-temperature, high-shear (HTHS) viscosity. A multigrade oil such as 10W-30 has to meet the requirements of both grades. The standard now includes very thin high-temperature grades such as 8, 12, 16 and 20, which are meant only for engines designed to use them. --- ## What do API categories such as SP and SQ tell you? The American Petroleum Institute (API) sorts petrol-engine oils into 'S' service categories and diesel-engine oils into 'C' categories. API SP, introduced in May 2020, added protection against low-speed pre-ignition (LSPI). API SQ has been licensed since 31 March 2025 and adds ultra-low-viscosity grades. For petrol engines, each newer category includes the performance of the earlier ones, so an SP oil can be used where a manual asks for SN. On a licensed bottle, the round API symbol known as the 'Donut' shows the service category at the top and the viscosity grade in the centre. API itself tells owners to check the owner's manual first. --- ## What do ACEA codes such as A5/B5 and C3 mean? ACEA, the European Automobile Manufacturers' Association, publishes oil sequences that each define a minimum quality level. The A/B class covers 'high SAPS' oils for petrol and diesel engines; SAPS stands for sulphated ash, phosphorus and sulphur. The C class covers 'low SAPS' oils that are compatible with catalytic converters and particulate filters. Within each class, the categories differ in high-temperature, high-shear viscosity: A5/B5 and A7/B7 are for engines designed for lower-viscosity oils and are unsuitable for some engines, while C3 and C4 call for a higher minimum. The 2023 sequences, published on 12 September 2023, added C7, a 0W-16 category. ACEA's own advice is to consult the owner's manual in case of doubt. --- ## Why do car maker approvals matter? Many oil labels also list approvals from vehicle manufacturers. These go further than the industry codes: they confirm the oil has been formally tested and approved for particular vehicles. They are specific, and similar-looking codes are not always interchangeable. Volkswagen's 508 00 and 509 00 specifications, for example, call for an SAE 0W-20 oil with an HTHS viscosity of at least 2.6 mPa·s and, according to the oil maker FUCHS, are not backwards compatible with earlier VW specifications. Your owner's manual lists the approvals your engine needs. --- ## How do mineral, semi-synthetic and full synthetic oils differ? The difference is the base oil. Conventional (mineral) oil uses base oil refined from crude oil, full synthetic oil uses synthesised base oils, and semi- or part-synthetic oil blends the two, with no agreed definition of how much synthetic it must contain. The word 'synthetic' on a bottle is therefore not a specification: the grade and approvals still have to match your engine. How oil type relates to service timing is covered in how often to change your oil in Oman. --- ## How do you choose the right oil for your car? Start with the owner's manual. Match the viscosity grade and every specification and approval it lists, because an engine may need several at once. For petrol engines a newer API category can stand in for an older one, but a different viscosity grade, ACEA category or manufacturer approval is not a safe substitute unless the vehicle manufacturer allows it. If the manual is missing or you are unsure, ask before the oil goes in: AutoTronix Express confirms the specified oil grade for your make, model and engine before an oil service. --- ## Common Questions **Is a thicker oil better in hot weather?** Not by default. Viscosity grades are matched to each engine's design, and ACEA notes that some categories are unsuitable for certain engines. Use the grade your vehicle manufacturer specifies rather than choosing by climate alone. **What do the Starburst and Shield symbols on a bottle mean?** Both are API certification marks. The Starburst identifies oils meeting the ILSAC GF-7A standard and is not used on 0W-16 oils. The Shield identifies ILSAC GF-7B oils and is used only for 0W-16. **Can I use API SP oil if my manual says SN?** Yes, for petrol engines. API states that the latest service category includes the performance of earlier ones, and gives SP in place of SN as an example. The viscosity grade and any manufacturer approval in the manual still apply. **Does an ACEA C3 oil suit every European car?** No. C3 is one category among several with different viscosity and SAPS levels, and ACEA warns that some categories are unsuitable for certain engines. Many European engines also require a specific manufacturer approval. --- ## Related Otto Explanations - How Often Should I Change My Car's Oil in Oman?: https://autotronix.om/otto/oil-change-interval --- ## Related Services - Oil & Filter Service: https://autotronix.om/express/oil-filter-service - Periodic Maintenance: https://autotronix.om/express/periodic-maintenance --- ## Book a Service WhatsApp: +968 9966 8600 https://api.whatsapp.com/send/?phone=96899668600&type=phone_number&app_absent=0 Location: Mabellah Industrial, Street 7, Muscat — Saturday to Thursday, 9 AM to 9 PM