Oil Viscosity (Grade)

The number before W shows cold performance; the number after shows thickness at operating temperature. Lower first numbers flow better at cold start. Manufacturers also require specifications like ACEA or API approvals. Many modern engines use very low viscosity oils such as 0W-20 or 0W-16 to reduce friction and fuel use.

Oil must be thin enough to reach parts quickly and thick enough to keep a film under load.

Using the wrong grade can affect oil pressure, hydraulic lifters and variable valve timing. Always follow the grade and specification in the manual.