Oil... how does it work? [split]

[Vovchandr]

@KillerBlackbird

Thinner for cold engine start up so it can flow to vital components of your engine better, but retain a specified weight when operating temperature (210*F) is reached so excessive engine wear does not occur.

Thinner than what?

If oil is made thinner for start up, it means it thickens up later no?

Or does it get even thinner once started?