What does the weight mean on a can of motor oil?

Using the right type of motor oil can prevent this from happening to you. See more car safety pictures.
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On every bottle of motor oil there is a seal that gives you three pieces of information:

  • The API service rating
  • The viscosity grade
  • "Energy Conserving" indicator (it either is or it isn't)

­The API service rating is a two-letter rating that tells you the type of engine the oil is meant for (gasoline or diesel) and the quality level.

The viscosity grade (for example, 5W-30) tells you the oil's thickness, or viscosity. A thin oil has a lower number and flows more easily, while thick oils have a higher number and are more resistant to flow. Water has a very low viscosity -- it is thin and flows easily. Honey has a very high viscosity -- it is thick and gooey.

Go to the next page to learn how viscosity is measured.