Passenger‑car motor oils over the decades have been formulated with a wide variety hydrocarbons base stocks, ranging from API Group I–III to synthetics such as Group IV and Group V esters, as well as bio-based materials. Each brings its own advantages and disadvantage, as engine technology has rapidly developed and requirements change.
Modern passenger‑car motor oils combine carefully selected base oils with advanced additive technologies to meet strict viscosity, engine‑protection, and fuel‑economy requirements. SAE J300 defines viscosity behavior across temperatures, while API, ILSAC and ACEA specs enforce performance standards. Over a century, oils evolved from simple mineral fluids to complex synthetic blends tailored for ever‑leaner engines, lighter viscosity categories, and extended drain intervals—covering every aspect from composition and testing to history and market trends.
Group III high‑VI mineral oils allow low-viscosity blends at lower cost. PAOs and esters are fully synthetic and offer superior low‑temperature fluidity and thermal stability.
Additives
Beyond base oil, PCMOs contain detergent, dispersant, anti‑wear, friction‑modifier, viscosity‑modifier, antioxidant and pour‑point agents.
- Ashless dispersants suspend soot and sludge, especially crucial for direct‑injection engines
- Wear additives, notably ZDDPs, form protective films
- Friction modifiers, such as molybdenum- and organic-based, create slick tribofilms essential in low-viscosity oils
- Viscosity modifiers (VIIs) improve viscosity index and stability across temperatures; especially vital in multigrade oils
- Oxidation inhibitors, validated via bench tests like ROBO, preserve low-temp flow over oil drains
SAE Viscosity Grades & J300 Standard
The SAE J300 standard defines multigrade and single-grade oil properties by temperature-dependent viscosity.
Cold grades: 0W, 5W, 10W, etc., rated via Cold Cranking Simulator (CCS) and pumpability tests
Hot grades: 20, 30, 40, 50, 60 measured by kinematic and high‑temperature, high‑shear (HTHS) viscosity
Recent additions: SAE 8, 12, and ultra-light 0W‑8 and 0W‑12—driven by OEM fuel‑economy needs
Performance Specifications
- API service categories (e.g., SM, SN, SP) impose limits on wear, oxidation, deposit control, and additives (e.g., max phosphorus)
- ILSAC GF‑series (GF‑4 to GF‑6, emerging GF‑7) add fuel‑economy and low‑speed pre‑ignition protection via tests like Sequence IIIG and IX
- ACEA, evolving from CCMC in the ’70s and formalized in 1996, often sets stricter standards for European OEMs
- JASO and JAMA (Japan) pioneer ultra-light grades (e.g., JASO 0W‑8 spec, proposed in 2017)
Characteristics & Trends
Lower viscosity grades (0W‑20, 5W‑20, 0W‑16) dominate due to fuel‑economy and emissions demands. Adoption of 0W‑20 took off around 2009–2010 with Honda/Toyota, and is now a leading global grade. Some OEMs recommend even lighter oils (0W‑16, 0W‑12); however, widespread commercial use remains limited. The trend is a decline in PCMO demand (down 45% U.S. since 2002), but their value has increased due to synthetic and premium formulations.
Historical Evolution
- The Society of Automotive Engineers (SAE) introduced viscosity classification in 1923.
- Multigrade oils emerged in 1955.
- The 1970s saw the introduction of 15W
- By the 1980s, 0W and 25W were introduced, as were plus pumpability tests.
- In the 1990s, high-temperature, high-sheer requirements were added
- The early‑2000s, bench oxidation tests (ROBO) became standard.
- In 2004 API SM, followed by SN, SP, tightening wear and deposit control.
- ILSAC GF‑6/SP in 2020 introduced new SLPI and LSPI protections.
- Lately, API SP now includes ultra-light grades; ILSAC GF‑7 and PC‑12 under development