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A code such as 5W-30 giving an oil's cold and hot viscosity behaviour.
Also known as: Multigrade oil marking
Sometimes confused with: Oil weight
An engine oil grade such as 5W-30 gives two numbers. The first, with the W, describes how the oil behaves when cold — the W stands for winter, not weight — and a lower figure means it stays thinner at low temperatures and reaches the bearings faster on a cold start. The second describes viscosity at operating temperature. A multigrade oil is not two oils: it is one whose viscosity changes less with temperature than a single-grade oil's does.
Gives cold behaviour before the W and hot behaviour after it, with a lower first figure meaning the oil stays thinner when cold and reaches the bearings faster on a cold start.
Contexts: Road signage, Vehicle dashboard
Uses W for winter rather than weight, which is the commonest misreading of the code and the reason drivers describe an oil as 'a 30 weight' when the number after the W is a viscosity class at operating temperature.
Contexts: Road signage, Vehicle dashboard
Describes one oil rather than two. A multigrade does not switch between grades; its viscosity simply changes less with temperature than a single-grade oil's does, which is what the two figures together record.
Contexts: Road signage, Vehicle dashboard
A numeral followed by a capital letter, then a short stroke and a second numeral, printed prominently on a container.
Both are consumable specifications a driver must match.