Encyclopedia of lubricants

Functions of Oil

Besides reducing friction between mechanical items, oil or lubricants have multiple functions. These include:

  • Cooling
  • Corrosion protection
  • Cleaning (binding of particles caused by wear and tear in engines and transmissions)
  • Sealing

Approvals & Suitabilities

describe which oil must be applied to which engine or transmission. API or ACEA (see below) values are insufficient to determine the correct application for a given oil type. The principles for Hengst are the same for oil as they are for filtration products: Original Equipment (OE) standards are the benchmark to ensure best performance. At times, certain customer market requirements may differ from what Hengst recommends.

EURO Standards

determine the emission levels for fuel operated engines. A higher EURO standard means stricter emission requirements or lower emissions. Both fuel and oil play an important role to keep emission levels down. For example, an engine oil which has been developed for EURO3 standards cannot be used for EURO6 engines. Using wrong or low quality oils can damage your engine and clog the entire exhaust system.


describes the extent to which a fluid resists a tendency to flow. “Low viscosity” lubricants are thinner than “high viscosity”, or thick fluids. Hot or cold temperatures, oil pressure and changing engine loads will affect oil viscosity. Determining the correct oil viscosity for each engine application is vital for achieving the best possible performance without causing damage to the engine or transmission. If the oil is too “runny”, the oil film can “burst”, preventing proper lubrication. Thick oil is sluggish and cannot move quickly through the engine or transmission making lubrication impossible. In both cases engine damage can occur.
Oil viscosity is represented by a number. The higher the number, the thicker the fluid. The first number in engine oils describes the viscosity for cold temperatures (W = Winter), the second number describes hot temperatures (summer). To ensure low fuel consumption, viscosities of 0W or 5W 20/30 are commonly used in modern engines.

Mineral Oils

can be altered with additive packages to enhance their performance and increase their range of applications. Today’s trend is clearly moving towards half and fully synthetic oils.

Half or Semi-Synthetic Oils

are somewhere between a mineral and a fully synthetic oil. The different molecule structures of semi-synthetic oils ensure optimized lubrication for older engines with larger tolerances. These oils also offer extended service intervals and better lubrication characteristics than pure mineral oils, without the high cost of fully synthetic oils.

Fully Synthetic Oils

use complex additive packages to achieve viscosity levels that mineral or semi-synthetic oils are not able to produce. Fully synthetic oils are mainly used in modern engines that have smaller tolerances, higher performance levels and longer service intervals. They are also generally more expensive than mineral or semi-synthetic oils.

ACEA (European Association of carmakers)

defines the quality standards and requirements for engine oil in Europe. ACEA categorises products with a combination of letters, numbers and year. For example: A3/B3 describes different characteristics than A1/B1, however higher numbers don’t necessarily indicate better quality.

API (American-Petroleum-Institute)

is an American interest group (like the ACEA) of the oil and gas industry. The API establishes technical standards and requirements for lubricants and assigns quality levels in engine oils. In general, the higher the letters, the higher the quality standards of the raw oil. These values apply to raw oil only, not to finished products. However, API values alone are not specific enough to determine the overall quality of engine oil and its performance levels.


A – Passenger cars (petrol engines)
B – Passenger cars, vans, light commercial (diesel engines)
C – Passenger cars for petrol and diesel engines with new exhaust after treatment systems (e.g. DPF)
E – Heavy duty diesel engines

SAE (Society of Automotive Engineers)

was established in 1911 to standardise oil and its viscosities. It is distinguished between single grade (e.g. SAE 20) and multi-grade (e.g. SAE 15W40) oils. Single grade oils are primarily used for applications with non-changing working conditions. Single grade oils are no longer used in modern engines or applications.

Base Oils

consist of five types of oils - out of which all engine and transmission oils are produced:

Group I

Most natural base oils for blending of oil products with low performance requirements.

Group II

Common base oils for the blending of mineral oil based products. Lubrication properties are valued as sufficient to good.

Group III

Group III oils are refined to the highest possible levels. Oil molecules remain stable and uniform, offering a wide range of applications. Although not chemically produced, these base oils are commonly used for blending full and semi-synthetic oils.

Group IV

Chemically produced base oils offering amazing performance potential for lubricants. Due to stable compounds and uniform molecules, these oils are a perfect base for the blending of full and semisynthetic oils.

Group V

Primarily used for the production of additives to improve other base oils and not as a base oil itself.

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