You’ve surely seen codes like 5W-30 or 10W-40 on oil containers, but what do they actually mean? Understanding them helps you choose well and look after your engine. Here’s the two-minute version.
A viscosity code
Those figures indicate the oil’s viscosity, that is, how fluid it is at different temperatures. Viscosity is key: too thick or too thin and the engine isn’t properly protected.
What does the “W” mean?
The W stands for Winter. The number before it indicates how the oil behaves in the cold: the lower it is, the better it flows when starting at low temperatures. A 5W starts better in the cold than a 10W.
And the second number?
The figure after the hyphen (30, 40…) indicates viscosity when hot, with the engine at operating temperature. The higher the number, the more body the oil keeps when the engine is hot.
Multigrade oils
Almost all modern oils are multigrade: they perform well both cold and hot, which is why they carry two figures. This protects the engine from the very first start to the most demanding use.
- 5W-30: very fluid when cold, common in modern cars.
- 10W-40: balanced, frequent in semi-synthetics and engines with a bit more mileage.
- 15W-40: higher viscosity, typical in diesel and industrial vehicles.
Always use the grade specified by the manufacturer in the service book: it ensures proper lubrication and keeps the engine’s warranty valid.
We’ll help you get it right
At Lubrimallorca we stock lubricants in every viscosity grade and advise you on the one your vehicle needs. Ask us with no obligation.
