Description
Multi-grade oils achieve their dual-viscosity rating through the use of special chemical compounds called Viscosity Index Improvers (VIIs). These additives are long-chain polymers that swell or unravel as the oil temperature rises.
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When Cold (W rating): The VIIs remain coiled, allowing the oil to flow easily (like the lower ‘XW’ number) to quickly reach engine parts during start-up, minimizing wear.
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When Hot (Y rating): The VIIs uncoil and thicken the base oil, preventing it from thinning out too much and ensuring the oil maintains adequate film strength and lubrication at high operating temperatures (like the higher ‘Y’ number).
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