Motor oil is one of the lesser-discussed yet extremely important components of a car, and it's a topic that shouldn’t be overlooked with the arrival of summer. Choosing the wrong type of motor oil can be harmful to your car in the long run, so it’s worth briefly reviewing the most important aspects of selecting the right oil for the summer.

What is motor oil and why is it important?

Drivers and experts alike know that motor oil plays an invaluable role, fulfilling essential functions to ensure the proper operation of internal combustion engines. Among its primary tasks is lubrication — reducing friction between moving metal parts (e.g., pistons, bearings), thereby minimizing wear. It also helps dissipate heat from the combustion chamber and points of mechanical friction.

Another crucial role is cleaning: the oil keeps tiny metal particles, soot, and combustion residues suspended so that they can later be filtered out by the oil filter. Additionally, it forms a thin film on metal surfaces, protecting them from rust — meaning it’s vital for corrosion prevention.

Last but not least, motor oil also contributes to sealing, helping to seal the space between the piston rings and the cylinder walls, which supports maintaining compression.

A quick overview of oil types

Although we’ve covered oil types in detail in another article, here’s a brief summary

•    Mineral oil: Refined from natural crude oil. Cheaper, but less resistant to heat and oxidation. Suitable for older or less demanding engines.
•    Semi-synthetic oil: A blend of mineral and synthetic oils, offering better heat resistance and wear protection — a popular mid-range choice.
•    Fully synthetic oil: Made from lab-designed molecules. Offers excellent properties — more stable under temperature changes, longer change intervals, ideal for modern engines.

What is viscosity and why does it matter?

Viscosity refers to the oil’s ability to flow at different temperatures. In general, oil needs to be thin enough when cold (e.g., during winter starts) so that it can reach engine components quickly, but also thick enough when hot to maintain proper lubrication.
Viscosity is rated on a scale, like 5W-30:
•    The 5W indicates the oil’s behavior in cold conditions (around -30°C), meaning it remains fluid enough in the winter.
•    The 30 refers to how viscous the oil is at high temperatures (around 100°C) — essentially, how "thick" it stays when hot.

How to choose the right oil?

The most important guideline is always the manufacturer's recommendation, which can be found in your vehicle's manual. Some additional points to consider:
•    Climate: In winter, choose oil with a lower “W” value; in hot summer weather, a higher hot-side viscosity is better.
•    Driving style: If you drive aggressively or do a lot of accelerating, synthetic oil with better heat resistance is advisable.
•    Usage type: For short city trips with frequent cold starts, use a finer, thinner oil.
•    Oil change interval: Some synthetic oils can last 15,000–30,000 km, while mineral oils may need replacing after 5,000–10,000 km.

What problems can arise from using the wrong oil?

In this area, rules are not just friendly suggestions — they are essential standards. Ignoring them can cause serious problems for your vehicle.

The most severe issues relate to the condition of your engine. Inadequate lubrication leads to premature wear of engine components, drastically shortening the lifespan of your vehicle.

Temperature extremes are another concern. Overheating can occur due to poor heat transfer or foaming, while cold starts may be problematic if the oil is too thick to circulate quickly. Thick oil can also increase internal resistance, which may result in higher fuel consumption.

And there are even more serious risks. In extreme cases, lack of proper lubrication may lead to piston seizure or crankshaft damage. Even worse — if you don’t use the manufacturer-specified oil in a new vehicle, they might refuse warranty coverage for repairs.