5W-30 vs 5W-20 vs 0W-20
Reviewed by GarageDex editorial
GarageDex's oil data shows the two numbers mean different things. The first number, before the W, rates how easily the oil flows when cold: lower flows faster at startup. The second number rates its thickness at normal operating temperature: 20 is thinner than 30. So 0W-20 and 5W-20 are equally thin once the engine is warm, while 5W-30 is thicker. The right grade is the one your engine specifies.
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| Grade | Cold-start flow | Thickness when hot |
|---|---|---|
| 0W-20 | Best | Thin (20) |
| 5W-20 | Good | Thin (20) |
| 5W-30 | Good | Thicker (30) |
0W-20 vs 5W-20
Once the engine is warm these behave the same, because the second number matches. The difference is cold starts: 0W-20 flows more easily in low temperatures, so it reaches the moving parts sooner. In a cold climate that is a real advantage. In a warm climate the two are very close.
5W-20 vs 5W-30
These start equally well in the cold, but 5W-30 is thicker at operating temperature. It suits engines designed for it, including many older engines and some turbocharged ones. Putting it in an engine designed for 20-weight oil does not add protection. It changes how the oil moves through passages sized for something thinner.
Why thin oil took over
American factory specifications moved from 5W-30 toward 0W-20 over the past decade, driven by fuel economy rules and tighter engine tolerances. See the year-by-year shift in when American cars switched to thin oil, and which grades lead today in the most common engine oil viscosity.
What it costs
Thin grades like 0W-20 are sold as full synthetic, at roughly $6 to $10 a quart. 5W-30 is also sold as conventional, from about $4 to $7 a quart, but only use conventional if your engine's specification allows it.
Ranges aggregated from published 2026 US repair-cost and parts price guides, including RepairPal and Car Talk. Prices vary by region, brand, and vehicle - treat these as a sanity check on a quote, not a fixed price.
Find your engine's grade
The grade is printed in the owner's manual and often on the oil filler cap. Look up your car's verified oil grade and capacity, and see synthetic vs conventional oil.
Frequently asked
What does the W in 5W-30 stand for?
Winter. The number before it rates the oil's cold-flow performance. A lower number means it flows more easily at low temperatures, which matters most at startup.
Is 5W-30 better protection than 0W-20?
Not automatically. Thicker is not simply better. An engine designed for 0W-20 has tight internal clearances and oil passages sized for thin oil, and it relies on that oil reaching the parts quickly at startup. Use the grade your manufacturer specifies.
Can I use 5W-30 instead of 5W-20?
Occasional use, such as a top-up, is unlikely to cause harm, but it is not what the engine was designed for. Return to the specified grade at the next oil change, and use the specified grade while under warranty.
Why do new cars use 0W-20 or even thinner oil?
Thin oil reduces internal friction, which improves fuel economy, and it circulates faster on cold starts, when most engine wear happens. Engines are now built with the tolerances to run on it.
Need your car's exact spec?
Find your car's oil type & capacity