A 5W-30 Is Not One Exact Viscosity
This is one of the most important things to understand about oil grades.
An SAE 30 does not have one exact viscosity.
It has to fall within a defined viscosity range.
That means one company’s 5W-30 can be slightly thinner or thicker at operating temperature than another company’s 5W-30 while both still meet the requirements of SAE 30.