Use of different weights of oil depends on the temperature range you expect to see during the period between changes. California is a pretty temperature stable state, so you don't have to worry about it.
Originally Posted by gh3ttotactic
Speaking of oil, wat's the diff. between 10-30 and 10-40 and when to use it??
Viscosity. 10W40 is too thick for a Civic, not to mention the shear problems that a lot of 10W40's have.