What Oil Viscosity for Southern California Car?

Any mods and where do you live? Location can have an impact on viscosity. I run 10W-40 as it gets pretty hot in Oklahoma and the car never sees the road from about mid-November through mid-March.
 
Any mods and where do you live? Location can have an impact on viscosity. I run 10W-40 as it gets pretty hot in Oklahoma and the car never sees the road from about mid-November through mid-March.
Zero mods - I'm in Southern California and for the past three weeks its been slightly over a 100 dees grees - average year around temp here I would say in the mid 70's 80's
 
I would go with what Bullitt347 suggested then. If you have good oil pressure then no reason to do anything else. If you have cats then stay away from lubricants with zinc, phosphorus, and sulfur as they have been shown to kill converters.
 
I would go with what Bullitt347 suggested then. If you have good oil pressure then no reason to do anything else. If you have cats then stay away from lubricants with zinc, phosphorus, and sulfur as they have been shown to kill converters.
I've been runing that Rotella 15-40 diesel oil, this time and last time. I gues on the next go around iI'll go with 10-40 but what brand would you consider.
 
Man I do not run oil that you would run so I am of no use there. I run Brad Penn with all the additives being I live in an emissions hospitable state. You need some of the SoCal guys to chime in here. I updated your thread title to get the to come out from under their rocks....
 
As I understand, diesel engine oils aren't a good substitute for gasoline engine oils. Something to do with the detergents if I remember correctly.

But I'm with @AeroCoupe - I run 10w40 in the summer months in my older flat tappet 302. I will probably do the same in my roller engine in the event I ever get it back in the car and running again. I don't think that either option would be horrible though - but I think that 40 will give you a microscopically thicker film to protect the bearings as compared to the 30 variant.