I live near Phx. AZ
And always used penn grade 20w 50
Because I thought it needed it for the heat here.
It used to consume about a quart of oil in 3000
Miles or so, and the lifters would always clatter when starting after sitting more then an hour.
I switched to penn grade 10w 30
It no longer consumes oil and no more lifter clatter!
I don't know exactly why but it's much happier!