Every oil bottle carries something like 5W-30, and almost everyone reads it as one measurement of thickness. It is two measurements of two different things, and understanding which is which explains most of the arguments people have about oil.
Across the vehicles we list, the grades break down like this:
| Grade | Rows |
|---|---|
| 5W-30 | 599 |
| 0W-20 | 378 |
| 5W-20 | 337 |
| 5W-40 | 103 |
| 0W-30 | 54 |
| 0W-40 | 19 |
| 10W-30 | 15 |
| 0W-16 | 13 |
The number before the W is about cold
The “W” is winter. The number in front of it rates how the oil flows when it is cold — at start-up, before anything is warm. Lower is better here, and it is not a small effect: most engine wear happens in the seconds after a cold start, while the oil is still making its way up to the top of the engine.
That is why so many manufacturers moved from 5W-20 to 0W-20 without changing anything else. A 0W-20 and a 5W-20 behave the same once the engine is hot. The 0W simply gets there faster in January. If your manual says 0W-20 and the shelf has 5W-20, those are not interchangeable in the direction you are hoping.
The number after the W is about hot
The second number rates viscosity at operating temperature. This one is chosen by the engine designer, and it is tied to how much room there is between moving parts and how hard the oil has to work.
- 20 and 16 go in engines built with tight clearances and a strong interest in fuel economy — the Toyota Corolla, RAV4 and Camry with the current four-cylinder family, for instance.
- 30 is the broad middle, and the most common single grade we list.
- 40 and 50 appear where the oil is asked to survive heat and shear: turbocharged European engines, and American performance V8s.
0W-16 is the newest arrival and still rare — thirteen rows in our data, almost all Toyota’s A25A/M20A engines, plus the second-generation Kia Niro from 2023. If your car asks for it, using a 0W-20 instead is a real change, not a rounding error.
Going thicker is not playing it safe
The common instinct — “I’ll put something heavier in, it’ll protect better” — is backwards on a modern engine. Variable valve timing systems are hydraulic: they use engine oil, through narrow passages, to move cam phasers. Feed them oil thicker than designed and they respond slowly or set a fault. On engines with tight bearing clearances, thicker oil also means less flow where flow is the point.
Going thinner than specified is the more obvious mistake, and both are avoidable by looking up the one number the manufacturer published for your engine.
Sometimes the grade is not the whole specification
This is the part that catches people out on European cars, and increasingly on American ones.
Volkswagen and Audi do not just ask for a grade, they ask for an approval printed on the bottle. In our data 21 rows require VW 502 00, 18 require VW 508 00 and 11 require VW 504 00 — see the A4 and Tiguan. A 5W-30 without the right approval is the wrong oil for those engines even though the numbers match.
Stellantis does the same on its performance V8s: nine rows require 0W-40 meeting MS-12633, and the newest Wagoneer books ask for MS-A0921. Mercedes-built engines in our data want MB 229-series oil.
There are ratings that work the same way. The Jeep Cherokee 2.0 turbo asks for API SN PLUS, a rating created specifically to protect small turbocharged engines against low-speed pre-ignition — a failure mode that can break pistons. And the diesel Mazda CX-5 accepts a 5W-30 only if it carries an ACEA C3 approval, because its particulate filter depends on the low-ash chemistry.
Where a specification like that exists, we show it as a note on the vehicle page rather than burying it, because the grade alone will send you home with the wrong bottle.
What to do with all this
Look up your exact year, model and engine — a Honda Accord, a Subaru Outback, a Chevrolet Silverado, a Hyundai Elantra — and use what it lists, including any approval.
And check it again when you change cars, even within the same model line. We have documented engines whose grade moved mid-life: Chrysler’s Pentastar V6 went from 5W-30 to 5W-20 for the 2013 model year, and its 3.7 and 4.7 did the same for 2007. The badge on the engine cover does not change when that happens. The manual does.