Engine oil labels - how to read them and what do they mean?

Engine oil is one of the most important preparations used in cars. Its task is to lubricate gasoline and diesel engines and thus keep them in good condition. Engine oil is also necessary to seal the drive unit and dissipate heat more effectively. That's why it's so important to know the basic markings of engine oil.

Engine oil - basic types

The division of engine oils by oil base is quite simple. According to it, the driver may deal with three types of oils:

1. Synthetic oil - Synthetic oils are the most technologically advanced types of engine oils. They are obtained as a result of chemical synthesis of hydrocarbons. They are characterized by low viscosity and resistance to high temperatures. Thanks to this, they are suitable both during maximum engine load and at low temperatures, and also provide effective protection of moving engine components.
2. Mineral oil - Mineral oils are preparations created in the process of refining crude oil. In practice, this means that mineral oil-based products are much more viscous.
3. Semi-synthetic oil - an intermediate product based on mineral oils and additionally enriched with synthetic.

SAE - the most popular classification of engine oil quality and its rules

The SAE standard is currently the most well-known and used worldwide when it comes to the classification of engine oils. Its name is an abbreviation of the Society of Automotive Engineers, an association of American automotive engineers.
SAE defines the markings of single-grade oils (10W, SAE: 40) and multi-grade oils (5W/30, 10W/40). The provisions used are so universal that users of engine oils around the world can easily find oil of the appropriate viscosity class when replacing it.
The marking with the letter "W" corresponds to the winter viscosity class. In the multigrade oil marking, the number before the letter "W" indicates the low-temperature viscosity class, and the second number indicates the high-temperature viscosity class.

According to it, the oil viscosity marking describes in one string the quality of the product at high and low temperatures.

API - American classification of engine oils

In the automotive world, SAE is not the only standard used to determine the quality of lubricant products. Another, quite well-known standard according to which the marking of engine oils is prepared is API, i.e. the American Petrol Institute. The designation of a specific oil is determined based on tests for various types of engines. During them, engine wear is examined after using a given oil, taking into account engine oil classification standards. According to API rules, oils intended for gasoline engines are designated with the letter S, and for diesel (diesel) engines with the letter C. Another letter is added to each of the above letters. The further it is in the alphabet, the newer standards the oil meets. Simply put: API oil markings are constantly evolving. Currently, the latest standard for gasoline engines is SP and for diesel engines CK-4. Oil markings may cover both categories: petrol and diesel, e.g. API SL/CF, which means that the oil can be used both in a petrol engine, where the manufacturer recommends the SL standard, and in a diesel engine, where the CF standard is recommended.

ACEA - European oil classification standard

Some time ago, Europeans followed the example of the Americans and created their own oil classification standard. ACEA - because we are talking about it - is an acronym that stands for the European Vehicle Manufacturers Association. Fortunately, the local marking system is quite transparent. The Ax/Bx designation refers to oils for gasoline and diesel engines of passenger cars and light commercial vehicles. The letter C refers to oils with low ash content, the so-called low-ash, intended for gasoline and diesel engines used in passenger cars and delivery vans adapted to the new EURO exhaust emission standards. The letter Ex refers to oils for heavily loaded diesel engines.

In the ACEA system, engine oils are described by a combination of the mentioned letters and numbers. The higher the number in the engine oil marking, the newer the standard.

Specification of car manufacturers, i.e. OEM

Rules for selecting the right engine oil

If you want to choose engine oil correctly, you need to remember a few very important rules.

1. We always rely on the manufacturer's opinion. He knows best what type of oil will be suitable for a given car. If, however, we have reasons to believe otherwise, it is worth asking for advice from an experienced technical advisor. It will take into account the markings of engine oil from other manufacturers and select the appropriate product for a specific engine.
2. It is worth choosing engine oil based on the wear and tear of the car and the kilometers traveled. If the car has already traveled a long distance, you should consider changing the oil to one that will provide greater protection for the engine and thus its durability. If higher viscosity oil was previously poured into the drive unit, do not use lower viscosity oils in its place. This involves an increased risk of leaks.
3. It is allowed to use other engine oil instead of the recommended one. For gasoline engines, the latest API category provides the properties of every previous category and can be used in older engines. If the manufacturer recommends oil that meets the API SN standard, API SP oil will provide full protection. In the case of diesel engines, the newer API standard usually meets the performance characteristics of the previous one, but not always. The same cannot be said for all requirements of ACEA standards. It is worth consulting a technical advisor in each case.
4. Oil markings are one thing, but the appropriate frequency of oil replacement is equally important. It is recommended that the engine oil be changed approximately once a year or after approximately 10,000 kilometers.

To sum up, engine oil markings inform the user about its properties both at low and high operating temperatures. When choosing the right product, you cannot rely solely on the labeling. It is also important to seek advice from experienced specialists. You can also search on the Internet, where all engine oil markings are very well described. Opinions of other users of a given oil may also be helpful.