Anything Auto Immune

Viscosity is an often-misunderstood term. It is commonly referred to as the “weight” of an oil, but weight is not a factor in how well an oil performs. By definition, viscosity is “the resistance to flow exhibited by a liquid.” The Society of Automotive Engineers (SAE) uses a numbering system to represent an oil’s viscosity at a specific temperature. The higher the number (30, 40), the more resistant (thicker) it is to flow. The lower the number (5, 10), the easier (thinner) it flows.
What does that mean to you?
Engine oils are required to work under extremely demanding conditions. For example, oil must flow easily at very cold temperatures in order to help cool and lubricate the engine. Consider the ice fisherman in Minnesota who tries to start the engine when the temperature is -10° F But the oil must also supply proper lubrication at very high temperatures. In this case, think of an Arizona angler towing his bass boat to Lake Havasu when the desert temperature tops 100°F.
Back when single-viscosity oils were the only choice on the market, some truck owners had to use a high-viscosity oil in summer and then switch to a low-viscosity oil in winter to ensure proper engine oil operation. Fortunately, modern oils are multi-viscosity, which means they are formulated to meet the challenging conditions of winter and summer. Such oils will carry a split viscosity designation such as SAE 5W-30, 1OW-40, or 1OW-50. (Note: the “W” in such designations does not refer to “weight.” It means the oil is rated for winter.)
If you live in an area where summer temperatures are moderate, but winter is foot-numbing cold, go with a 5W-30 oil. If you live in a more temperate climate, you can opt for a 1OW-30 or 10W-40 oil. The former is best where winters are cold but not bitingly so and where summer sees a few 100° F days; the latter is the choice if you experience mild winters but endure long periods of hot weather— and if you regularly tow a trailer or haul heavy loads, If you live in the desert where temperatures exceed 100° F for weeks at a time, go with 20W-50.

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