Choosing engine oil: viscosity and standards

Choosing the right engine oil is essential for engine life and drain intervals. Viscosity, standards and manufacturer recommendations: here are the key points.

Viscosity (e.g. 5W30, 10W40)

The first number (5W, 10W…) indicates cold flow: the lower it is, the better the oil circulates at start-up. The second (30, 40…) indicates hot viscosity. 5W30 oil suits most modern engines (petrol and diesel) and varied climates. 10W40 or 5W40 remain common for older or high-mileage engines.

ACEA and manufacturer standards

ACEA standards (e.g. A5/B5, C3) define performance levels (petrol, diesel, catalyst, DPF). The service book or handbook give manufacturer recommendations (e.g. Renault RN0710, VW 504 00). It is important to meet at least the recommended type and standard to keep warranty and avoid failures (turbo, DPF, timing).

Synthetic, semi-synthetic, mineral

Synthetic: better durability and cold performance, often recommended for modern engines. Semi-synthetic: price/performance compromise. Mineral: mainly for older engines. When in doubt, follow the service book.

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