Viscosity modifiers ensure that the viscosity of the fluid is close to constant over as wide a temperature range as required by the application (cold cranking versus maintaining a film when the engine is running hot, for example).
The polymers used to achieve this improve the viscosity index (a fluid’s change in viscosity relative to temperature) but can degrade under shear, causing permanent viscosity loss. Over time, polymer chemistry evolved to improve resistance to mechanical breakdown while maintaining thickening efficiency. Temporary shear loss can be desirable under certain circumstances, but permanent shear loss isn’t desirable most of the time.
Historically, shear stability became critical with the adoption of multigrade engine oils. Early VMs were prone to degradation, prompting innovation in polymer structures that could withstand high shear conditions found in engines and gear systems.
Regionally, North America and Europe emphasize shear stability due to stringent viscosity retention requirements in engine oil specifications.
Asia-Pacific growth reflects increasing adoption of multigrade oils and modern equipment.
Market trends show growing demand for shear-stable formulations as specifications mandate lower viscosities for fuel efficiency while maintaining protection. Shear stability remains central to lubricant durability across global markets.