The Ins and Outs of Oil Viscosity

Understanding what oil viscosity is, and knowing how to determine the right oil viscosity for your vehicle is vital to ensuring that your engine is protected. In this article, I am going to explain the different types of oil viscosity, and how you can find the right oil for your motor vehicle.

What is Oil Viscosity

Oil Viscosity - What it is

Viscosity, in a general sense, is the measure of any liquid’s resistance to flow. To be more specific, there are two ways viscosity can be viewed: kinematic viscosity or dynamic viscosity.

Kinematic viscosity is a fluid’s resistance to flow and shear due to gravity. If a given lubricant’s viscosity is lower, it will flow faster. For example, if you pour two containers, one filled with water, and the other with syrup, you would notice that the water flows faster due to its lower viscosity. Kinematic viscosity determines oil’s high-temperature viscosity grade. This is where the “30” in 5W-30 synthetic oil comes from.

Alternatively, there is dynamic viscosity, which is essentially the amount of energy required to move an object through the lubricant. Dynamic viscosity is measured using the Cold Crank Simulator test, and is used to determine an oil’s low-temperature viscosity grade. This would be the “5W” in Amsoil XL 5W-30 Synthetic Motor Oil.

Additionally, you should be aware of what exactly the viscosity index (VI) is. The viscosity index refers to how much the viscosity of a lubricant changes due to fluctuations in temperature. Oil’s VI is measured at 40°C and 100°C. IF a liquid’s viscosity does not change much between these temperatures, it will have a higher VI and vice versa. You can find the VI of an Amsoil motor oil on its product data sheet. Synthetic Amsoil products generally have a high VI rating, making them more stable than competitors’ products. Find out more about the benefits of synthetic Amsoil motor oil.

How Does Viscosity Affect Your Engine?

Viscosity is the most important property of oil when considering engine protection. Viscosity determines how your engine’s lubricant will react to changes in speed, pressure, and temperature.

For example, during cold winter months, it may be difficult to get your car to start first thing in the morning. This is because colder temperatures cause lubricants to thicken and require more energy to circulate due to reduced flow. As a result, your vehicle’s crankshaft has to push through thick oil in order to spin fast enough for your car to start. This can cause components in your engine to experience wear and tear. However, when the weather is warmer, the oil becomes thinner and easier to circulate. Amsoil products offer a wide variety to choose from in order to accommodate any engine.

What Happens If You Use the Wrong Oil Viscosity?

Depending on whether the viscosity of your oil is too high or too low, you might experience several problems, such as poor fuel economy, increased wear on your engine, and increased chemical breakdown.

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Low-Viscosity Oil

Low-viscosity motor oil may be too thin, and can compromise the protection of your engine over time. A thin lubricant may not be able to adequately fill the gaps between engine component in order to prevent contact between them.

These effects can be worsened by extreme heat and stress levels. When temperatures rise, oil becomes thinner. If your oil is already thinner than it should be for your vehicle, then extremely hot temperatures are going to cause your motor oil to not be able to develop a thick enough film to prevent metal to metal contact.

Oil that is too thin for your vehicle can lead to engine components wearing out and can lead to insufficient oil pressure.

High-Viscosity Oil

Many consumers make the mistake of assuming that motor oils with higher viscosities are always the best option due to them usually offering better protection against wear. However, this is not always the case.

First of all, thicker oils are much more difficult to circulate throughout the engine.  This makes your vehicle much less fuel-efficient. This can also make it more difficult to start your vehicle, which can increase engine wear.

Just as how thinner oils become even worse in warm weather, the disadvantages of thicker oil become more important during colder months. When temperatures drop, oil becomes thicker.  This puts significant strain on your battery, and may even leave you unable to start your vehicle.

Lastly, high-viscosity oil is not able to transfer heat between engine components as easily as low-viscosity oil is able to. Moreover, thicker oil can increase internal operating temperatures, which can ultimately lead to engine failure as oil passages become blocked by sludge.

How to Choose the Right Oil for Your Vehicle

As mentioned throughout this article, it is crucial that you pick the oil with the ideal viscosity for your vehicle in order to protect against engine wear. Fortunately, determining the viscosity needed for your vehicle should be relatively easy.

The owner’s manual of your vehicle should specify which oil viscosity you should be using for your engine. Often, the manual may specify multiple options to choose from depending on the weather. For example, it may recommend 5W-30 synthetic oil for warmer weather, and 0W-30 oil for colder weather. Amsoil products will specify the viscosity of the oil across the front of the packaging.

Additionally, you should understand what the numbers identifying different viscosities mean. For example, the “5W” in 5W-30 refers to the lubricant’s ability to flow in cold temperatures. The lower this number is, the easier it will be able to flow in cold weather. Meanwhile, the “30” in 5W-30 indicates the fluid’s ability to flow at a vehicle’s normal operating temperature, which is 100°C. If this number is higher it means that the oil will remain thicker at operating temperature. So, in the above example of 5W-30 vs 0W-30, both would operate the same at operating temperature while the latter would flow better in cold weather.

Understanding the implications of using oil’s of different viscosities is extremely important in order to ensure the longevity of your vehicle and its engine. While there are additional factors to consider, such as how often you should change your oil, oil viscosity should be one of your top priorities when it comes to vehicle maintenance. Fortunately, Amsoil motor oil comes in a wide range of products to fit any vehicle.

If you have any further questions regarding Amsoil oil, or the different types of motor oil, contact us at

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