Why shear stability determines the performance of an oil
Shear stability describes the resistance of an oil to mechanical destruction of its molecular structure under shear stress – i.e. when the oil is exposed to high forces in narrow gaps or between moving metal parts. High shear stability means that the oil retains its viscosity and therefore its lubricating properties even under intensive stress.
Relevance in the industry
Shear stability is a key quality factor in lubricant technology, particularly for engine oils, hydraulic oils and gear oils. It determines whether an oil provides reliable protection under high loads or whether it “shears off” and thus loses its lubricity. Particularly in modern downsized engines, high-pressure pumps or transmissions with fine tolerances, high shear stability is essential for long-term use.shear stability protects against oil degradation under load. Now understand how it is measured and why it is so important for modern technology.
What happens if shear stability is too low?
The oil is mechanically degraded, its viscosity drops and it can no longer form a stable lubricating film. This leads to increased wear and, in extreme cases, to expensive engine damage or failures in hydraulic systems.
How is shear stability measured?
Typically, the so-called tapered roller test bench according to ASTM D6278 is used, in which the oil is mechanically stressed over defined cycles. The extent to which the viscosity has decreased is then measured.
Is a higher viscosity index synonymous with high shear stability?
Not necessarily. The viscosity index describes the temperature dependence, while the shear stability relates to the mechanical load-bearing capacity. Both values are important – but independent
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