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.
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.
 
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Simply pull out the owners manual and follow the manufacturers directions.
Don't overthink it. ;)

Owners manual 40+ years old and lubrication technology has advanced in 40+ years by quite a bit. I don't think it it is over thinking rather more like understanding what is available today that is better than the offerings 40+ years ago.
Thank you, thats exactly what my inner voice just said to me -
 
I'm sure you're correct but exactly why is that -
Well first it contains additives that are bad for cats, zinc I believe is one that is bad for cats so if your running diesel engine oil and no cats you're ok. If you have cats stop using that oil, it takes a lot of miles, like many oil changes before cats show effects.
There may be other reasons not to use it but that's the one I know about
Sorry, didn't see the post from faster above.
 
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