Engine Oil Analysis - Viscosity Oil Testing

The analysis of engine oil through viscosity testing

Engine Oil Viscosity is a measurement of the resistance of a fluid being deformed by either shear stress or extensional stress. It can also be thought of as a measure of fluid friction. There are many different types of ways of expressing a fluid's viscosity. Here at OCLS, we choose to calculate the fluid's kinematic viscosity. The kinematic viscosity is the ratio of the viscous force to the inertial force (or density).

It can be defined as:

Where:

v = Kinematic Viscosity (cSt [Centistokes])
µ = Absolute Viscosity (cP [Centipoise])
ρ = Density (g cm ^-3 [grams per centimetre-cubed])

Simply speaking, the lower the viscosity value, the thinner the oil will be. Which follows that a high viscosity value indicates a thicker oil. For example, water has a viscosity of about 1 cSt. An average engine oil has a viscosity of about 100 cSt.

Viscosity is a very important property of oil that allows it to protect the internal workings of a machine by creating a thin film of oil between moving parts. Viscosity can be affected by many factors and so regular monitoring is essential. The test is generally carried out on industrial machinery such as engines, hydraulics, gearboxes etc.

Oil is a non-Newtonian fluid, which means that its viscosity is not constant - it cannot be described by a single number - it varies. For example, a temperature increase by only 5°C can cause the viscosity of some fluids to double! OCLS checks viscosities routinely at 40°C, but other temperatures up to 100^oC are used. Oil viscosity can be affected by many factors and so regular monitoring is essential.

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Using the Wrong Viscosity Oil

Oil viscosity too high

Inadequate flow to components
Energy consumption losses occur
Excessive heat generation causing varnishes and sludge's
Poor oil flow in cold-start conditions

Oil viscosity too low

Lack of protective oil film between components
Excessive wear
Oil film fails at high temperatures or high loads
Increase in friction, resulting in heat generation
Internal or external oil leaks

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We work to
ISO9001:2008 and
BS EN ISO14001:2004 standards