Motor oil glossary
Plain-English definitions of the oil terms you'll see on a bottle or in your owner's manual. Each links to a fuller explanation.
- Viscosity
- How thick an oil is and how easily it flows. Lower viscosity = thinner; higher = thicker.
- SAE J300 grade
- The industry standard that classifies oils by cold-flow (the W number) and hot viscosity (the second number), e.g. 5W-30.
- W (Winter) rating
- The number before the W. It rates how easily the oil flows when cold — a lower number flows better on cold starts.
- Multigrade oil
- An oil that meets a cold-flow rating and a hot-viscosity rating at once (e.g. 5W-30), so it works across a wide temperature range.
- Specification (oil spec)
- A performance standard the oil must meet (API, ILSAC, ACEA, or an OEM approval) — separate from the viscosity grade. Match both.
- API service category
- American Petroleum Institute gasoline-oil category, such as API SQ today or API SP in many recent manuals.
- API SQ
- The current API gasoline-engine oil service category introduced with the ILSAC GF-7 family. Match it only where the manual or approved replacement path supports it.
- ILSAC
- Fuel-economy oil standards used alongside API categories, including GF-7A / GF-7B today and GF-6A / GF-6B in many recent manuals.
- ILSAC GF-7
- The newer ILSAC gasoline-oil family: GF-7A uses the Starburst branch, while GF-7B is the separate 0W-16 Shield branch.
- ACEA sequences
- European oil classes (A/B, C, E) covering gasoline, diesel, low-SAPS and heavy-duty needs.
- dexos
- General Motors’ oil specifications (e.g. dexos1 Gen3 for gasoline) layered on top of API/ILSAC.
- LSPI
- Low-speed pre-ignition — abnormal combustion mainly in turbo direct-injection engines; modern specs test against it.
- HTHS viscosity
- High-temperature high-shear viscosity — how the oil protects under heat and load. Lower HTHS aids economy.
- Base oil group
- API classification of base oils (Groups I–V). Synthetic oils use higher groups; it affects quality and the spec, not the grade.
- Additive package
- Detergents, dispersants, anti-wear (e.g. ZDDP), viscosity modifiers and antioxidants blended into the base oil.
- Synthetic vs conventional
- Synthetic oils are engineered for better cold flow and stability; conventional is mineral-based. Either must still meet your spec/grade.
- Oil change interval
- How often to change the oil — set by your manufacturer for your engine and driving conditions, not by a shop sticker.
- Severe service
- Tougher driving (short trips, heat/cold, towing, dust, idling) that usually calls for a shorter oil-change interval.
- Oil capacity
- How much oil the engine holds (with filter), in quarts or liters — specific to the year/make/model/engine.