5W-30 and 10W-30 are the same thickness at full operating temperature (both are 30-grade), but 5W-30 flows better on cold starts while 10W-30 is thicker when cold. Use whichever grade your owner's manual specifies for your engine and climate.
Attribute
5W-30
10W-30
Cold-start flow The lower first number flows better at low temperatures.
5W — flows better when cold
10W — thicker when cold
Hot viscosity (100 °C) Both give the same film thickness when hot.
30 — identical
30 — identical
Cold-climate suitability
Better for cold winters
Better suited to mild or warm climates
Typically specified for
Many modern engines, broad temperature range
Older engines and warmer-climate use
Bottom line: Same hot thickness, different cold flow — follow the grade your manual specifies for your climate.
The one real difference
Both oils are 30-grade, so at full operating temperature they hold the same film thickness — there is no hot-running difference between them. The meaningful difference is cold behavior. 5W-30 has the lower first number, so it stays thinner and pumps faster when the engine is cold; 10W-30 is thicker at low temperatures and takes a little longer to circulate on a cold start.
That gap only matters as temperatures drop. In mild or warm conditions both grades reach a healthy oil pressure quickly. In a cold winter, the faster cold flow of 5W-30 reduces the brief period of reduced lubrication right after start-up, which is why many modern engines specify a 5W grade.
Which should you use?
Use the grade your owner’s manual specifies for your engine and climate. The two share identical hot viscosity, so the choice between them is essentially a cold-flow and climate decision, and the manufacturer has already accounted for that in its recommendation.
Some manuals list both grades across a temperature chart, allowing 10W-30 above a certain ambient temperature and 5W-30 below it. If yours does, follow that chart. If only one grade is listed, use it. And remember that viscosity is separate from specification: whichever grade you run still has to meet the oil standard or approval your manual requires.
Frequently asked questions
Is 5W-30 thicker than 10W-30?
No. They are the same thickness when hot because both are 30-grade. 5W-30 is the thinner of the two only when cold, which means it flows faster on a cold start.
Can I use 10W-30 instead of 5W-30?
Only if your manual lists 10W-30 as acceptable for your engine and climate. They match when hot, but 10W-30 is slower to flow on cold starts, which matters most in cold weather.