Paraffin oils are regular oils.
Synthetic oils are "built" from mostly ethylene molecules to exactly what the chemist wants.
Multi-viscosity oils act like the first number when cold and the second number when hot. That being said, a 5W-30
oil would have the viscosity of a 5 weight at 20 degrees and the viscosity of a 30 weight at 200 degrees. Even the Winston Cup guys use multi-viscosities oils, mostly
synthetic.
Bob