# What engine oil 5W-30 means

*2026-10-01 · autotools*

The 5W-30 on an oil can is its viscosity grade. It describes how freely the oil flows at a cold start and in an engine at working temperature.

## The first number and the W

W stands for winter. The number before it shows how well the oil flows in the cold: the lower the number, the faster the oil reaches the engine parts on a cold morning.

## The second number

The second number shows how thick the oil is in a warm engine. 30 is a common choice for many modern engines.

## The approval matters more than the grade

Oils of the same grade are not all equal. The car maker requires a specific specification or approval, written in the service book.

* Find the required grade in the service book
* Check the maker's approval or specification
* Choose an oil whose label states that approval

If in doubt, ask us: we advise from your car's details. See all [engine oils](/en/c/engine-oil).

## Products in this article

- [Castrol Magnatec 5W-30 engine oil](https://autotools.ee/en/products/castrol-magnatec-5w-30-mootorioli-cas-5w30-magnatec-c3) — €63.81 (€12.76/l)
- [Castrol Edge 5W-30 engine oil](https://autotools.ee/en/products/castrol-edge-5w-30-mootorioli) — €18.81 – €65.61 (from €16.40/l)
- [Castrol GTX RN17 5W-30 engine oil](https://autotools.ee/en/products/castrol-gtx-rn17-5w-30-mootorioli) — €12.51