How to read motor oil labels?
Motor oil should be changed regularly—either after a certain number of kilometers or periodically, depending on how the car is used. However, regular oil changes do not eliminate the need to monitor the oil level in the engine.
In professional workshops, mechanics usually select the appropriate oil themselves, using catalogs and manufacturer specifications. But what if, during a long trip, you need to top up the oil yourself? That’s when knowing how to read the labels and symbols on the packaging becomes invaluable.
What does oil viscosity mean?
The most common marking on motor oil labels is a symbol consisting of two numbers separated by the letter “W”, such as 5W-30 or 10W-40. This is the SAE (Society of Automotive Engineers) viscosity classification.
The first number (before the “W”) refers to how the oil performs at low temperatures, while the second indicates its lubricating properties at high engine temperatures. The lower the number before the “W,” the better the oil performs in freezing conditions. Conversely, the higher the number after the dash, the better the engine protection under high thermal loads.
Quality standards – API, ACEA, ILSAC
In addition to viscosity, labels also display quality ratings according to various organizations. One of the most commonly used is the API standard, primarily used in North America. These markings consist of two letters. The first indicates the engine type—“S” for gasoline engines and “C” for diesel engines. The second letter refers to the oil’s quality and the specific engine requirements it meets.
In Europe, the ACEA classification is more common. It categorizes oils into groups A/B (for gasoline and diesel engines), C (low-SAPS oils), and E (for heavy-duty vehicles). You may also encounter the ILSAC rating, which is mostly used for Japanese and American vehicles.
Types of motor oils – synthetic, semi-synthetic, and mineral
Motor oils are divided into three main categories based on their chemical composition: synthetic, semi-synthetic, and mineral. Synthetic oils offer the highest quality and best performance. They are produced through advanced chemical processes, which give them excellent thermal stability, low viscosity at cold temperatures, and strong protection against mechanical wear.
Semi-synthetic oils are a blend of mineral base oil and synthetic additives. They offer decent engine protection at a lower cost than fully synthetic oils.
The simplest and most affordable are mineral oils, produced by refining crude oil. These are mainly used in older engines that do not require advanced lubrication properties.
Why the best oil isn’t always the best choice
It might seem logical that the highest-performing oil would be ideal for any engine, but that’s not always the case. Each engine is designed with a specific viscosity grade, lubrication properties, and oil base type in mind. Oil that is too thin may not maintain proper pressure in the system, while oil that is too thick might not reach all engine components quickly enough.
Additionally, modern engines equipped with diesel particulate filters (DPF) or variable valve timing systems require oils formulated to meet strict emission and durability standards. Using an oil that doesn’t meet these specifications can lead to faster wear and even permanent damage to engine components. That’s why—even when choosing a reputable product like Castrol engine oil – it’s crucial to ensure the selected variant matches your vehicle’s specifications.
This article was created in collaboration with Junipertrade – a supplier of motor oils and lubricants for passenger cars, trucks, and agricultural machinery.
