Originally Posted By: Cristobal
Over 100 degrees F. every day.
As long as your cooling system is in working proper order, there's no need to jump up 2 grades to a 20w-50. 0w-xx, 5w-xx, 10w-xx, 15w-xx, and 20w-xx will all still be operating at the xx viscosity. Being in a hot climate just means you don't need 0w-xx or 5w-xx, and you can benefit from the better shear stability of 10w-xx, 15w-xx, or 20w-xx oils. This is why I recommended 10w-30 above to the OP. 15w-40 probably wouldn't hurt too much, but 20w-50 is absolutely overkill for a vehicle specifying 30 grade oils.
Now, if you
really wanted to, you could run 15w-30 for the best possible shear stability in a hot climate that doesn't ever see temperatures below, I don't know, maybe 60 degrees Fahrenheit.
Here is a dual rated API CJ-4/SM 15w-30 oil from Delo that seems promising, but costs twice as much per gallon as the (dual rated) Delo 10w-30 I linked previously:
https://www.amazon.com/Delo-400-15W-30-Motor-gallon/dp/B017AX1XFA/
The only vehicles that really need a 20w-50 would be major leakers, burners, or high performance vehicles constantly revving over 5,000 RPM.