The numbers on a motor-oil container may confuse you. We can easily explain them at CMA's Valley Volkswagen in Staunton, VA.

Those numbers show motor oil's viscosity. Scientists use viscosity to classify fluids by their ability to resist flow. To visualize this concept, think about spilling two glasses. One contains water, and the other contains molasses. Obviously, the water would flow much easier than its counterpart. Molasses, which significantly resists flow, is a high-viscosity liquid. Neither substance is suitable for your engine, of course.

Auto manufacturers supply ideal oil viscosity ratings in their vehicles' manuals. Each rating contains a hyphen. For example, you might recognize 5W-30 or 0W-20 from your manual. These numbers actually provide viscosity ranges. In 5W-30, the left value tells us the oil's viscosity before you start the engine, and its companion provides the viscosity when you're driving your vehicle. For your engine's health, always use the oil viscosity recommended by the manufacturer.

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