What sort of engine oil should I use in my car? Viscosity, manufacturer’s specifications and the risks of using the wrong oil

Engine oil for a car should always be selected in accordance with the car manufacturer’s instructions. The correct oil will have the correct SAE viscosity, ACEA classification and, where applicable, manufacturer-specific approval. If you are topping up the oil yourself, check the details in the owner’s manual or service documents before opening the container. Different engines in the same car model may require different oils, so the car make, model year or oil colour alone are not sufficient criteria for making a choice.

Engine oil for cars: SAE viscosity indicates how the oil behaves

The SAE designation, such as 0W-20 or 5W-30, indicates the oil’s viscosity grade. The number preceding the letter ‘W’ relates to the oil’s cold-weather properties, whilst the number following it relates to the oil’s behaviour once the engine has warmed up. The designation should not be interpreted to mean that a higher number always provides better protection. The engine is designed for a specific oil, and the manufacturer may specify its own approved alternatives for different conditions.

If the dipstick shows that the oil level is close to the lower limit, you should primarily top up with the same oil that is already being used in the engine. Adding a small amount at a time helps to keep the level under control. If you do not know what oil was last used in the car, do not choose a product based solely on viscosity. At the same time, check the required specification and the manufacturer’s own approval.

You can only find the right engine oil when the viscosity, ACEA classification and manufacturer’s approval all match.

The ACEA classification indicates the performance of engine oil

The ACEA classification specifies the performance requirements for engine oil. These classifications relate, amongst other things, to engine type, wear protection requirements and compatibility with exhaust after-treatment systems. Oils for European passenger cars often carry classifications such as A/B or C. ACEA sets minimum requirements for oils, but car manufacturers may specify more precise characteristics. ACEA oil classifications will be supplemented as engine technology advances.

Class C oil is not a generic term for all modern cars, nor can Class A/B oil be substituted for it at your own discretion. The additives and properties of the oil may differ, even if the viscosity rating is the same. Using the wrong grade may mean that the engine or exhaust after-treatment system does not meet the required standards. It is therefore advisable to check the entire list of specifications on the oil container label.

The manufacturer’s approval is key to choosing the right oil

Manufacturer-specific approval is often the most accurate guide when choosing an oil. This may be a combination of letters and numbers specified by the car manufacturer for that particular engine. An oil may be SAE 5W-30 and belong to the ACEA class, but it may still lack the approval required by your car. Check the requirements in the owner’s manual, service schedule or the manufacturer’s documentation before topping up or changing the oil.

We do scheduled maintenance in accordance with the manufacturer’s service programme for all car makes and models. As a rule, we use original or equivalent spare parts, and we record the servicing in the manufacturer’s electronic service log. If your oil consumption has changed, the engine is making an unusual noise, or you’re unsure about the correct oil grade, we’ll investigate the situation fault diagnosis before we decide on the next steps.