Kinematic viscosity – flow rate of a lubricant
Kinematic viscosity describes the flowability of a liquid under the influence of gravity, i.e. how quickly an oil “flows” at a certain temperature. It is specified in mm²/s (formerly: centistokes, cSt) and is a key parameter in the selection and standardization of engine oils, gear oils and industrial lubricants.
Typical measuring points are 40 °C (for ISO viscosity classes) and 100 °C (for engine oils according to SAE J300).
Why is kinematic viscosity so relevant for lubricants?
Viscosity influences how well an oil adheres between friction surfaces, how easily it can be pumped and how well it compensates for cold or heat loads. Oil that is too thin can lead to insufficient lubrication, while oil that is too thick can lead to friction losses and energy inefficiency.
BASINOL lubricants are produced according to precisely defined viscosity profiles to guarantee optimum performance in a wide range of applications – from highly stressed industrial bearings to modern car engines.
How is kinematic viscosity measured?
It is determined using a so-called capillary viscometer. This involves measuring how long a defined volume of oil flows through a glass tube under gravity – at a precisely controlled temperature. The most common measuring points are 40 °C and 100 °C, as they simulate practical conditions in everyday operation.
What does the viscosity value say about the performance of the oil?
A higher value means that the oil is more viscous – it tends to form a thicker lubricating film, but is more difficult to pump. A lower value indicates that the oil is thinner – it gets into small channels more easily, but the film tears more quickly under load. The optimum value therefore depends on the engine design, the application and the ambient temperatures.
How is kinematic viscosity related to SAE or ISO classes?
SAE grades (e.g. 5W-30) and ISO grades (e.g. ISO VG 100) are both based on kinematic viscosity – just with different classification logics:
BASINOL products are precisely classified according to both systems.
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