Frequently Asked Questions

What are the main functions of engine oils?

Engine oil is a critical fluid in an internal combustion engine. One needs to ensure the engine always has enough oil. The main functions of oil are discussed below:


Oil reduces friction between metal surfaces to the minimum. This is achieved by means of a lubricant film which is formed between the surfaces of the structural parts of a running engine. This film substantially reduces friction and consequently reduces wear and heat generation. The service life of the engine is thus increased several times. The oil film prevents such problems as pistons seizing and bearings damage, besides, it reduces fuel consumption. It is critical for the oil to have viscosity not too high for easy start of the engine. On the other hand, the oil must not become too free-flowing at high temperatures otherwise the oil film can be ruptured causing insufficient lubrication. Another important function of the oil film between the cylinder sleeve and rings is to provide a thin hermetic sealing of the combustion chamber from the crankcase.

Cooling down

When starting a cold engine, it takes a few seconds for the piston to reach the operating temperature. A few minutes are needed for the whole engine block to reach the operating temperature depending on the outside air temperature, engine type and motion mode. The engine must be cooled to maintain the operating temperature and prevent overheating. First of all it means using the two most popular cooling media which are air and water. However oil contributes to a substantial part of the cooling, primarily inside the engine. Pistons in modern engines have cooling channels supplied with oil by means of spraying nozzles. As a result the piston crown is additionally cooled.

Protection against corrosion and sludge deposit

Combustion results in forming aggressive substances which are neutralized by lubricant oil. The combustion residue and foreign materials are driven by the oil flow to the oil filter to be sifted there or to be deposited at the oil bath case. To provide a good flow of oil and good cleaning function it is critical to use high-quality oil complying with the requirements specified by the vehicle manufacturer.

Can mineral oils and purely synthetic oils be blended? Can gasoline and diesel engine oils be blended?

Oils which are made for the same purpose and which meet the same quality classifications can usually be blended, regardless of whether they are single- or multi-grade oils, mineral or purely synthetic oils. However, blending of oils meant for different purposes – e.g., those for diesel and gasoline engines – is not recommended. Nonetheless, the best way to guarantee uniform quality is to use the same oil between oil changes.

Which factors have an impact on oil consumption?

In addition to the mechanical condition of the engine, oil consumption is most affected by the viscosity of the oil used, the volatility of the base oil, the degree of filling and the manner of driving. Usually, thin oil is consumed faster than thicker oil. Thin oil passes through the clearances to the combustion chamber more easily and also to outside of the engine through any leaking seals.

The manner of driving probably has the greatest impact on the oil consumption of a normal engine in good condition when using high quality oil. During short-distance trips the oil level can even raise at first as a result of dilution by gasoline due to frequent starts of the enrichment system. The engine oil used can contain more than 10% gasoline.

Oil consumption is increased most by prolonged use of the accelerator pedal with frequent engine braking. In this case the oil heats up and becomes thinner, as a result of which the vacuum from the engine braking draws a lot of it into the combustion chamber through the clearances. Sometimes after long city trip some fuel enters the oil and then evaporates quickly due to higher working temperature during longer trips. This results in seemingly large consumption of oil. In this case it is recommended to check oil approximately every 1000 km run when the added oil usually stays inside the engine.

Do some oils tend to have higher consumption than others?

Consumption of thin oil is greater than that of thick oil. This is a general rule, but sometimes there are exceptions: for example, when changing the oil grade, consumption may be higher before the first oil change. Besides, a new engine usually consumes more oil than normal whilst running in. All in all, the engine should consume some oil, although it is lubricated to a sufficient degree by a very small amount of high-quality engine oil.

Why are oil changes important?

The oil properties gradually diminish in use, the impurities content increases, and the additives become less effective. Sufficiently frequent oil changes remove the impurities from the engine and improve the lubricating properties of the product. The purpose of additives in high-performance engine oil is, among other things, to help keep the engine clean and prevent corrosion, resulting in less wear and longer engine life. Besides, high-performance oil keeps the engine and catalytic converter in good condition and the lubricating properties of the oil as good as those of new oil. This results in cleaner exhaust gas emissions and lower fuel consumption.

How often should the engine oil be changed?

Oil must always be changed no later than the maximum number of driven kilometers specified by the car manufacturer. Winter driving, short trips, dusty conditions, etc., require more frequent oil changes. Sufficiently frequent oil change is the cheapest way of prolonging engine life.

What are the most common causes of low oil pressure in an engine?

The pressure can be low for a number of reasons:

  • Worn or damaged oil pump

  • Faulty oil pressure regulator

  • Clogged oil channels or air filter

  • Worn engine.

  • Switching from one oil to another can result in foaming

  • Fuel entering oil reduces its viscosity

  • Presence of coolant in the oil

  • Oil is unsuitable for the application as it has low viscosity.

What does 0W-40 mean?

This is the SAE viscosity classification for engine oils indicating the winter and summer application of oils. The classification has been made on the basis of oil viscosity (or thickness) without taking any other properties into account.

What is the difference between GL-4 and GL-5 oils?

API GL-4 oils have less EP (extreme pressure) additives and are normally used for the transmission of front-wheel drive vehicles. API GL-5 oils are normally used in the so-called hypoid drive gears. Oils in this class contain double amount of EP additives. The API class must be selected according to the vehicle manufacturer’s instructions. Using a lower class may result in more rapid wear of parts, whereas using a higher class may cause poor synchronization in manual transmission.