Okay, so I remember seeing the same post a few months ago, but I cant find it now, so I have to ask, what weight oil should I really be using in Southern California with temperatures ranging 32F to 110F. My old man always told me to put 10W-30 in everything "Just do it and stop asking questions." But I happened to be going through the shop manual and I just barely notice that it really calls for 10W-40 in temperatures above 90F. Is this true? Should I switch to 40? Have I harmed my engine when I have driven it in 110 degree weather?