The recommendation is based on both ambient temperatures and operating conditions. It is always best to follow the manufacturer’s recommendation for the weight and whether to use a multi-grade or straight-weight oil in your motor. This time is used in a formula to determine the viscosity. The oil is then timed on how long it drains to the stop mark. After the test material comes to the test temperature, the oil is drawn above the start mark. A capillary tube is used to measure viscosity. After allowing the test material to equalize to the test temperature, the viscosity can be measured. The sample is placed in a heated bath at a set temperature (40☌ or 100☌). The dominant procedure for performing viscosity measurements is an ASTM D445 - or centistoke - test. So, a 15W-40 oil will have a slower flow rate than a 10W-30. The second number represents the viscosity at operating temperature.įor example, a 15W-40 oil has a viscosity grade of 15 at 0 degrees Fahrenheit and 40 at an operating temperature of 212 degrees Fahrenheit. Remember, the higher the number, the thicker the oil. The ‘W’ stands for “Winter,” so it’s easy to remember the first part of a multi-grade oil’s name is in reference to cold weather viscosity. Thin oils have a lower viscosity and pour more easily at low temperatures than thicker oils with a higher viscosity. The oil’s viscosity determines how easily oil pours at a specified temperature. The first number in the series represents the cold weather viscosity. This means that the oil flows differently at various temperatures. Let’s break this down further. This is the most common type of oil used in modern automotive engines. The lower the weight, the quicker it spreads out on this angled table.Īside from straight-weight oils, there are also multi-grade oils. This photo demonstrates how oil behaves at verifying viscosities. Straight-weight oil will be named something like SAE30, for example. These oils are uncommon in modern vehicles, but some small engines and older model vehicles will sometimes recommend a straight-weight oil. Straight-weight oils have a set viscosity, a single grade. There are a few different ways to categorize motor oils. Motor oils use a rating system developed by the Society of Automotive Engineers (SAE) to classify oil by viscosity. A lower viscosity index indicates that the oil’s viscosity can be significantly affected by temperature change. If the oil’s viscosity doesn’t change significantly between the two testing temperatures, it has a high viscosity index - meaning the viscosity does not fluctuate with temperature change. A fluid is tested at 100 and 212 degrees Fahrenheit. The viscosity index does not use units - instead, it is only measured by temperature change. To account for those differences, we can calculate the change in oil viscosity from temperature fluctuations to find the viscosity index. Every type of oil has a unique formula that changes how it behaves. For example, water poured into a glass will flow much faster than molasses, which is more dense.Ī fluid like oil has many ingredients and quality factors that can affect its viscosity, especially at changing temperatures. Every liquid will have a rate at which it moves, though each behaves differently under gravity due to its viscosity. Kinematic viscosity measures oil’s resistance to flow due to gravity. This difference occurs because water has a lower dynamic viscosity. You require less energy to glide through water than trudging through molasses. To put this concept in perspective, imagine walking through water vs. Maintain operation in extreme temperaturesĭynamic and kinematic oil viscosities are necessary measurements when considering which lubrication products are best for your engine.ĭynamic - or absolute - viscosity is the measure of a lubricant’s resistance to flow and its ability to behave under high pressure.Lessen particle contamination sensitivity.Choosing the right viscosity for your application will: Oil separates two metal surfaces and allows them to glide against each other rather than grinding and wearing down the material. Oil viscosity will impact how vehicles, equipment and other machines perform. High-viscosity oil is more robust and thick - like honey or molasses - making it ideal for industrial, heavy-duty machinery which operates at higher temperatures. Thinner oil has a lower viscosity, similar to water, pouring more effectively and allowing the engine to start much faster in colder weather. This behavior contributes to the oil’s ability to flow through the engine. Specifically, motor oil will thin out as the temperature increases and thicken as it cools. Viscosity is the consistency of a liquid before and after internal friction is applied.
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