Lubricant Knowledge
Sample: Understanding engine oil viscosity grades
What the numbers on an engine oil label mean, and why choosing the grade your vehicle manufacturer recommends matters.
1 min read
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The numbers printed on an engine oil pack, such as 20W-50 or 5W-30, describe the oil’s viscosity grade under the SAE system. The first number, followed by “W” for winter, relates to how the oil flows when cold; the second relates to its thickness at normal operating temperature.
Why the grade matters
Engines are designed around a particular oil thickness. Using the grade listed in your vehicle handbook helps the oil reach moving parts quickly at start-up and maintain a protective film once the engine is hot.
Checking your handbook
- Find the recommended SAE grade and any performance specification (for example an API category).
- Match both when choosing an oil.
- Ask the Tethys team if you are unsure.
