5W-30 or 5W-40: what does it mean and which to use?
The numbers look cryptic but are quickly explained. We show what matters.
To the factsViscosity in two numbers
A label such as 5W-30 describes the viscosity, that is how thick the oil is. The number before the W stands for cold behaviour in winter, the number after it for the thickness at operating heat. With 5W-30 and 5W-40 the cold behaviour is the same, the difference lies in the heat.
5W-40 is a little thicker at heat than 5W-30.
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Sorted out factually
- What your car needs is fixed: what counts is the approval and viscosity from the manual, not the general comparison.
- 5W-30: often required for modern engines with fuel-saving and longlife specs.
- 5W-40: frequently for engines that need a slightly thicker oil at heat or are more highly stressed.
- Do not swap on your own: only change if both values are approved for your engine.
Said honestly
There is no generally better oil between 5W-30 and 5W-40, only the one approved for your engine. Anyone who switches to another value without approval risks, in the worst case, damage or warranty problems. Look in the manual and stick to the specification. We give you the facts, the decision stays with you.
Sources and further reading
- Viscosity , Wikipedia