How to Read Oil Viscosity

by Michael Marcus
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Michael Marcus

Motor oil viscosity, or thickness, is given by an alpha-numeric code on the can. This code describes how thick the oil is, and what sort of engines it is meant to lubricate.

Reading the Oil Viscosity

Step 1

Find the motor oil weight on the oil can. This is usually a number code that looks like this: 10W-30.

Step 2

Read the viscosity rating. On the pictured oil can, the viscosity is 10W-30.

Step 3

Understand the viscosity. The first number in the code is the starting viscosity. This rates the thickness of the oil when the engine is first started. 10W oil has a viscosity rating of 10 at winter temperatures. The second number is the high temperature viscosity. When this oil is heated by the engine, it was a viscosity rating of 30.

Step 4

Check your the owner's manual of your car to make sure that you are using oil of the correct viscosity rating. Modern car engines are designed to run at specific temperature ranges and for proper lubrication they require oils rated for their operating temperatures.

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