How to choose oil?

How to choose oil?

Saving on engine oil does not pay off in the long run, but sometimes we have no other choice. Most often, however, not the best oil selection is the result of belief in superstition and - let's face it - quite complex oil descriptions and classifications

How to choose oil? We advise you on how to choose the best oil

The engine wears out the most, not when it is hot and the car travels another hundreds of kilometers. 90 percent wear falls on the moment of commissioning and the first kilometers before reaching operating temperature. The colder it is, the worse engine oil performs its role.

It is because of the use of cars on short routes that problems arise with the extension of timing chains, wear of turbochargers or failures of exhaust gas recirculation valves. The better the oil, the more such defects can be postponed - and vice versa.

Viscosity - this is the most important thing

Speaking of viscosity oils, we will not use abstract terms such as internal friction of liquids. Although from a technical point of view this is a mistake, it is more understandable for most car owners to say that a more viscous oil is thick and a low viscosity oil is more watery. Oil viscosity or density is its most important parameter affecting protection, or premature engine wear.

However, the viscosity changes substantially as the temperature changes - the warmer it is, the more watery the oil becomes, although rarely too watery. And vice versa: the colder it is, the more oil it thickens. However, not every oil changes its properties to the same extent. The viscosity grade, which is usually marked on each oil pack, usually in the largest letters, e.g. 15W-40, 10W-40, 5W-40, 5W, tells how it will behave in the winter when the car stops at night or during normal engine operation. -30 etc.

Oil viscosity table

Photo: Auto Świat

Poorly selected oil viscosity in winter can significantly damage the condition of the engine.

What oil is better for summer?

The oil viscosity class described with a digital-letter code (e.g. 15W-40) informs how the oil reacts to a temperature drop and what is its viscosity during normal operation of a warm engine. The number before "W" (from winter - winter) describes the winter properties of the oil, and the second number (20, 30, 40, 50 or 60) the summer viscosity.

However, this description can be misleading for many. Some engines fit tightly and require aqueous oil, while others require slightly thicker oil, creating a thicker film that provides greater protection. Oil density at operating temperature (in practice around 100 ° C) describes summer viscosity grade.

However, as you can guess, it has nothing to do with the time of year. A normal, functional, water-cooled engine has almost the same operating temperature, regardless of whether it is frost or heat outside!

It is only important for what oil viscosity the engine was designed for.

What oil is better for the winter?

The situation is different when it comes to winter viscosity. This parameter (i.e. 0W, 5W, 10W or 15W) determines the minimum temperature at which oil will allow the engine to start. The lower the number before "W", the lower the temperature at which the oil retains its fluidity (which does not mean that it has adequate lubricating properties).

Two issues are important. First, any oil at negative temperatures is too thick to provide efficient lubrication. Secondly, however, the more watery the oil, the faster it starts working as it should, the lower the load on the starter, battery and alternator, the shorter the engine runs "dry".

Therefore, oil with lower winter viscosity is always better for the engine than oil with high viscosity. It's not just winter.

What oil is better for the whole year?

If someone thinks that 5W-40 oil is too watery for his engine, so he uses 15W-40 or even 10W-40, he is very wrong. At operating temperatures, e.g. up to 100ºC, the viscosity of 5W-40, 10W-40 or 15W-40 oils is the same!

The difference appears only when we leave the car overnight and the oil thickens. When starting, the oil with lower winter viscosity starts working faster and thus reduces engine wear. Always, regardless of the season!

Therefore, 5W-40 oil is better than 15W-40 and better than 10W-40. It can even be said with full responsibility that when the temperature drops below -25ºC, using 15W-40 oil is the best way to break the engine. Oil 5W-40 is not so rare for an engine that can be lubricated with 15W-40 oil.

What oil is better for older cars?

There are often questions: my car already has 200,000 km mileage - should I replace the oil with mineral oil? Answer: absolutely not - this will only accelerate engine wear.

For the same reasons, oils with worse winter properties should not be used - e.g. 10W-40 instead of 15W-40. If leaks, sweating gaskets, etc. appear, then the fault should be repaired, and not spoil the engine with oil with too weak properties just to reduce the leakage for a short time. \

Unless we expect the car to end soon - anyway. However, certain combinations related to the selection of oil are allowed, which temporarily postpone the need for repair and generally do not harm. So you can use oil for cars with greater mileage, which has additives softening the seal and reducing leaks.

However, the 100,000 mentioned by the producers should be treated km only as an advertising slogan - firstly, the engine after such a mileage does not require special oil, and secondly, it is not the mileage that counts, but the condition of the engine.

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In very old cars, it is also allowed to use oil with higher summer viscosity - e.g. 5W-50 instead of 5W-40. However, it is worth consulting your choice with a mechanic who knows what is wrong with our car - perhaps more viscous oil will not help at all, and even hurt.

When can this happen? There are engines in which the channels through which oil flows, e.g. to the engine head, are so narrow that too viscous oil is not able to circulate in them, as is required by e.g. camshaft.

Synthetic or mineral oil?

Other frequently asked questions relate to the use of synthetic oil or simply with better viscosity parameters for a car that has been used for some time on cheap mineral oil, e.g. 15W-40.

This is a common case: since we already know that good oil protects the engine better in winter (but also in summer), we will gladly use it, but many are afraid of flushing carbon deposits with additives in synthetic oil. Drivers have doubts that better oil, especially synthetic oil, will not leak the engine.

The answer is: the risk is very small. It is worth realizing that if we have, for example, a 15-year-old car, now it is impossible to buy the same oil that was available 15 years ago, and it does not cause any danger to engines, on the contrary.

If for some time we used a weak oil, which had poor cleaning properties, you can replace it a little earlier than usual after the first use of a good synthetic. This operation will definitely not hurt the engine, but on the contrary - it will help.

Choose oil step by step

1. Check what oil your car's engine needs. The newer the car, the more difficult the task, which especially applies to diesel engines. We must consider not only the viscosity class, but also the ACEA quality (string of characters, e.g. A3 / B3 / C3), followed by the manufacturer's standard, e.g. GM-LL-B-025.

2. Start by finding oils with the right viscosity, e.g. 5W-30.

3. From the available oils in the right viscosity, find those that have the right quality according to ACEA, eg A3 / B3, A3 / B4.

4. Check that the oil meets the appropriate manufacturer standard. All standards met are listed on the packaging or in the oil description on the website. This is especially important for some diesels (e.g. VW with unit injectors).

5. In the case of semi-synthetic and mineral oils used for an older car, you can settle for two parameters: viscosity and intended use of the oil for the selected type of engine - diesel or gasoline. You can also choose a universal oil, which is the majority of them.