The oil properties gradually diminish in use and the number of impurities increases. Sufficiently frequent oil changes remove the impurities from the engine and replace them with high-performance oil. The additives in high-performance motor oil help keep the engine clean and prevent corrosion, resulting in less wear and longer engine life. In addition, 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 achieves cleaner exhaust gas emissions and lower fuel consumption.

Selection of the right lubricant is influenced by both the operating conditions and the following criteria, which are important to take into account: - Right viscosity: (SAE classification) The engine must start even in extremely low temperatures, and the oil must reliably lubricate the engine also in high temperatures and under heavy load. - Right quality: (API and/or ACEA classifications) The oil quality has an impact on the oil change period. The properties of a high-standard motor oil last longer and enable long intervals between oil changes, recommended by the manufacturer. The vehicle manufacturer gives the minimum requirements and the viscosity classifications for the motor oil in the vehicle manual.

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

Engine oil, or engine lubricant is any of various substances (comprising oil enhanced with additives, for example, in many cases, extreme pressure additives) that are used for lubrication of internal combustion engines. The main function of motor oil is to reduce wear on moving parts; it also cleans moving parts from the sludge, inhibits corrosion, improves sealing, and cools the engine by carrying heat away from moving parts. Motor oils are derived from petroleum-based and non-petroleum-synthesizedchemical compounds. Motor oils today are mainly blended by using base oils composed of hydrocarbons, polyalphaolefins (PAO), and polyinternal olefins (PIO), thus organic compounds consisting entirely of carbon and hydrogen. The base oils of some high-performance motor oils contain up to 20% by weight of esters.

Automobile engines have many moving parts. As these parts move and rub against each other, the force of friction creates heat. Oil lubricates the engine and absorbs heat, allowing the internal parts to work together effectively without overheating.

Oils which are made for the same purpose of use and which meet the same quality classifications can usually be blended, regardless of whether they are single- or multi-grade oils. However, blending of oils meant for different purposes of use – 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.