In contrast to SAE 10W-40 oil, SAE 5W-30 oil flows better in cooler climates. Sinopec Lubricant supplier told us that when determining the first number (SAE 0W, 5W, 10W, etc.) for oil, they test it at a lower temperature than when determining the second number (SAE 30, 40, 50, etc.). For applications involving high loads and temperatures, the engine is better protected in this way. On the other hand, oil viscosity at operating temperatures is indicated by the greater number to the right of the “W.” Higher values indicate an oil viscosity that is thicker. The oil won’t get as thick in the chilly winter months the lower that amount is. The number to the left (before the “W”) of a quart of oil’s viscosity grade, which denotes oil viscosity tested at lower temperatures, is the quart’s winter rating. They eventually developed multi-grade oils such as SAE 10W-30, 5W-30, 20W-50, and so on. Low viscosity oil in the SAE 10W grade was very prevalent throughout the winter, whereas SAE 30W grade was more often used in the summer (higher oil viscosity). These were referred to as winter and summer grades. They used to produce motor oils for both cold and warm temperatures decades ago. What exactly does the “W” in oil stand for? Have you ever pondered about it when staring at a bottle of SAE 10W-40 or another multi-grade engine oil? Contrary to popular belief, the “W” stands for “winter” rather than “weight.” What kind of motor oil is best? It is one in which no matter what the temperature, the oil’s viscosity would remain constant. In general, a complete synthetic oil has a greater viscosity index than regular motor oil. The engine is better protected with motor oil with a high VI. Oil viscosity changes less in proportion to temperature the higher the VI number. How do they calculate engine oils VI? They measure its viscosity across a broad temperature range. Keeping in mind the olive oil example? In other words, VI assesses an oil’s resistance to resisting both getting thicker at lower temperatures and thinner at higher temperatures. The viscosity index calculates the relationship between viscosity and temperature variations. If you put it in the refrigerator for a few hours, it thickens and flows more slowly. Because shampoo has a greater viscosity than coffee, it flows more slowly from the bottle.Īnother example is olive oil. Try the same procedure with a shampoo bottle. What transpires? Right, it comes out of the cup. Pour a cup of coffee into the sink to serve as an example. Film strength is effectively maintained at higher temperatures by using an oil with a greater viscosity, such as an SAE 40 or 50. In cold weather, thin oils have a lower viscosity and flow more readily than thick ones, which have a greater viscosity and pour more slowly.įor instance, when the temperature is cold, low-viscosity oils like SAE 0W or 5W minimize engine friction and enable engines to start quicker. Oil’s viscosity fluctuates as temperature changes. It must be thick enough to create a coating that keeps engine components apart while remaining at a low enough level to prevent excessive energy waste. To create the lubricating layer between the engine’s metal components, oil viscosity is required.
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