Oil Viscosity Grade Numbers (e.g., the 10W and 30 in 10W-30 oil) represent the oil’s viscosity range and limits, not its actual viscosity. Since viscosity varies with temperature, the temperature must be specified for accurate readings.
For example, a 30 grade oil has a kinematic viscosity of about 10 cSt at 100°C, ideal for most engines, but around 250 cSt at 24°C, which is too thick. A 10W grade oil, on the other hand, has a viscosity of about 5 cSt at 100°C (too thin) and around 30 cSt at 24°C (more acceptable).