Choosing lubricants for an internal combustion engine is not just buying liquid in a beautiful canister, but a complex engineering task on which the resource of the unit directly depends.
Many car owners get lost in a sea of specifications when trying to figure out what exactly their car needs, because the wrong choice can lead to costly repairs.
In this article, we will look at the main criteria to determine which engine oil is best for your specific case, based on the manufacturer's technical specifications and tolerances.
Base: synthetic, semi-synthetic or mineral water
The fundamental difference between oils lies in their base, which determines stability at extreme temperatures and durability.
Synthetic oils are created through chemical synthesis, which allows the molecules to be the same size and shape, providing ideal fluidity and protection.
They are best suited for modern engines with high operating temperatures and complex exhaust filtration systems.
Mineral oils obtained by direct distillation of petroleum contain many impurities and have an unstable molecular structure.
Their use is justified in older engines with large clearances or in units where high loads are not provided.
Semi-synthetics is a compromise option, where up to 50% synthetics are added to the mineral base, which improves the characteristics, but does not bring them to the level of pure synthesis.
⚠️ Attention: Never mix oils on different bases unless absolutely necessary, as this can lead to sedimentation and coagulation of additives.
It is worth noting that modern European engines practically not designed for the use of mineral oils due to environmental and fuel economy requirements.
The choice in favor of synthetics is often dictated not only by the desire to extend the life of the engine, but also by the need to comply with strict maintenance regulations.
Viscosity and SAE standard: reading the numbers correctly
The most common classification a driver encounters is the system SAE, indicating the viscosity of the oil at different temperatures.
The numbers before the letter W (Winter) indicate low-temperature viscosity, which determines the ability of the oil to be pumped in cold weather.
The second number after the letter W characterizes the viscosity at engine operating temperature (about 100 degrees Celsius) and the ability to maintain a protective film.
For example, the popular oil 5W-30 will remain liquid at temperatures down to -30 degrees, but when heated its viscosity will correspond to class 30.
For hot climates or older engines with worn bearings, thicker oils such as 10W-40to maintain system pressure.
Below is a table of correspondence between temperature ranges and viscosity:
| SAE Viscosity Grade | Min. cranking temperature (°C) | Min. pumping temperature (°C) | Viscosity at 100°C (cSt) |
|---|---|---|---|
| 0W | -35 | -40 | < 3.8 |
| 5W | -30 | -35 | < 3.8 |
| 10W | -25 | -30 | < 4.1 |
| 15W | -20 | -25 | < 4.4 |
Using too viscous oil in winter can lead to oil starvation in the first seconds after startup, which is critical for the resource.
On the other hand, excessively thin oil in summer will not be able to create the necessary protective film, which will cause metallic knocking and wear of the rubbing pairs.
API and ACEA specifications: what is more important for your car
In addition to viscosity, it is critical to pay attention to the tolerances and specifications developed by international associations and automakers.
API (American Petroleum Institute) - American standard, where the marking “S” (Service) is intended for gasoline engines, and “C” (Commercial) is for diesel engines.
The second letter denotes generation and quality: the further it is from the beginning of the alphabet, the higher the class (for example, SN better than SL).
European standard ACEA is considered more stringent and oriented towards modern environmental and fuel economy requirements.
ACEA categories are divided into A/B (petrol and light diesels), C (catalytic converters) and E (heavy diesels).
Many car manufacturers such as Mercedes-Benz, BMW or VAG, have their own unique tolerances, which must be indicated on the canister.
If the instructions for your car indicate approval MB 229.5, using the oil without this confirmation may void your warranty.
What is the difference between ACEA A3/B4 and A5/B5?
A3/B4 are oils with high viscosity and stable film for powerful engines, often made in Europe. A5/B5 are low viscosity (energy saving) oils that flow easier, but require very precise engine assembly. They should not be mixed or used for other purposes.
Additive packages and their effect on engine performance
The base oil makes up only 70-80% of the volume of the canister, the rest is a complex cocktail of chemical additives that determine the final properties of the product.
Antioxidant additives prevent oil aging when exposed to oxygen and high temperatures, extending the drain interval.
Detergents and dispersants are responsible for keeping the engine clean by keeping combustion products and carbon deposits in suspension until filtered.
Anti-seize (EP) additives create a strong film on the metal surface that prevents metal-to-metal contact under high loads.
Modern oils also use friction modifiers to improve fuel efficiency.
It is important to understand that There is no universal oil that is ideal for all engines at once., since additive packages are customized for specific tasks.
For example, oils for turbocharged engines contain an enhanced package of antioxidants due to the high temperature in the turbine area.
When switching to another brand of oil, it is advisable to flush the engine, since additive packages from different manufacturers may conflict with each other.
Replacement intervals: myths about 15,000 kilometers
Car manufacturers often indicate replacement intervals of 15,000 or even 20,000 kilometers in service books.
However, these figures are relevant for ideal operating conditions, which in reality are extremely rare.
Severe conditions include short trips (less than 10 km), traffic jams, cold climates, dust and towing a trailer.
In such operating modes, engine oil oxidizes much faster, losing its protective properties long before the scheduled mileage.
Experts recommend reducing the replacement interval by 1.5–2 times from that stated by the manufacturer if you drive mainly in the city.
For turbocharged engines, an interval of 10,000 km is considered the maximum reasonable limit, regardless of what is written in the instructions.
☑️ Signs that it's time to change the oil
Ignoring this rule leads to the formation of sludge, stuck piston rings and failure of hydraulic compensators.
Frequently asked questions about choosing and changing oil (FAQ)
Below are answers to the most popular questions that car owners have when choosing lubricants.
This information will help you quickly navigate and make the right decision for your car.
Is it possible to mix oils from different manufacturers?
Technically, modern oils are compatible, but this should only be done in emergency cases (topping up on the road). During a scheduled replacement, it is better to completely drain the old oil and not take risks, since the chemical composition of the additives may differ.
Is it true that synthetics need to be changed more often than mineral water?
This is a common myth. Synthetic oils are more stable and last longer than mineral oils. However, due to their high cleaning power, they become more quickly contaminated with wear debris in older engines, which visually creates a feeling of rapid loss of properties.
How to determine if the oil is fake?
Pay attention to the quality of the label's printing, the presence of security codes that can be checked on the manufacturer's website, and the price. Too low a price is a sure sign of counterfeit. It is also important to buy oil only from trusted stores.
Do I need to flush the engine every time I replace it?
If you pour the same oil and observe the intervals, flushing is not necessary. It is only required when switching to another type of oil (for example, from mineral water to synthetic) or if the engine is very dirty.