Oil Grades Explained (0W-20, 5W-30, 15W-50 & More)
Confused by all the numbers and letters on an oil bottle? You're not alone. This plain-English guide explains what engine oil grades and specifications actually mean — so you can choose with confidence.
Short version: always use the grade and approval listed in your owner's handbook (or check our Oil Finder). Read on to understand why.
Reading a grade: what "5W-30" means
Engine oils are graded by the SAE (Society of Automotive Engineers) viscosity system. Take 5W-30:
- 5W → the "Winter" rating: how easily the oil flows when cold. A lower number = thinner when cold = easier cold starts and faster protection on start-up.
- 30 → how thick the oil stays at engine operating temperature (~100°C). A higher number = thicker film at temperature.
So a 0W-20 flows very easily cold and is thin when hot (great for fuel economy in modern engines), while a 15W-50 is thicker both cold and hot (suited to high-performance, older or hard-worked engines).
These are multigrade oils — they perform across a wide temperature range, which is exactly what you want in Australia's varied climate.
Common grades and where they're used
| Grade | Typical use |
|---|---|
| 0W-20 | Modern petrol/hybrid engines built for maximum fuel economy. Thin, efficient. |
| 5W-30 | The most common modern grade — many petrol and diesel engines, including low-emission (C-spec) engines. |
| 5W-40 | Turbo petrol/diesel, European engines, warmer conditions. |
| 10W-40 | Older engines, some 4WDs, high-kilometre vehicles. |
| 15W-50 | High-performance, racing, older engines, heavy-duty/hot conditions. |
| 15W-40 / 20W-60 | Older diesels and heavy-duty applications. |
Thicker is not automatically "better protection." Using a heavier grade than specified can reduce fuel economy and, in modern engines with tight tolerances, actually reduce protection. Match the spec.
Beyond viscosity: specifications & approvals
The grade is only half the story. Modern engines also need the right specification:
API (American Petroleum Institute)
Petrol standards run API SN → SP (newer is better/backwards-compatible); diesel uses CK-4 and similar. Higher letters = newer performance standard.
ACEA (European)
- A/B — petrol and light-duty diesel.
- C1, C2, C3, C4 — low-SAPS ("low sulphated ash, phosphorus, sulphur") oils for engines with DPFs and catalytic converters. Using the correct C-grade protects your emissions system.
OEM approvals (carmaker-specific)
Some manufacturers require their own approval, printed on the bottle:
- GM dexos (dexos1 petrol, dexos2/dexosD diesel)
- VW 502.00 / 504.00 / 507.00 (VW, Audi, Škoda, SEAT)
- Mercedes-Benz MB 229.x
- BMW Longlife, Ford, and others.
If your handbook names an approval, use an oil that carries that approval — not just the matching grade.
Why the wrong oil is a costly mistake
- DPF damage: A high-ash oil in a modern diesel can clog the diesel particulate filter — a very expensive repair.
- Poor economy & performance: Wrong viscosity means more drag or less protection.
- Warranty risk: Not meeting the manufacturer's oil spec can affect a warranty claim.
Getting it right is cheap insurance. That's what our Oil Finder is for.
Full synthetic vs semi vs mineral
- Full synthetic — best protection, flow and durability; ideal for modern, turbo and performance engines. (Most Penrite Enviro+ and racing oils are full synthetic.)
- Semi-synthetic — a middle ground for many everyday engines.
- Mineral — basic protection, older or low-demand engines.
Modern vehicles almost always specify synthetic.
Australian conditions
Heat, towing, 4WDing and stop-start traffic all put load on your oil. The good news: your manufacturer's recommended grade is already chosen to cope with a wide temperature range. Stick to spec, change it at the right interval, and your engine's well looked after.
The bottom line
- Find your grade and approval (handbook or Oil Finder).
- Choose an oil that meets both.
- Change the filter too.
- Not sure? Ask us — we're happy to confirm.
Related: Oil Finder · Safety Data Sheets