extreme cold pending for DFW...

[Japanese]

Ambient temp shouldn't affect your decision on the oil grade. Just the winter rating.

Yes, it should because those temps. affect the optimum engine cooling. It causes stress on the cooling system (water pump, thermostat, radiator fan) and hence the oil system too. Check this thread out:
https://bobistheoilguy.com/forums/threads/stopped-by-an-auto-parts-store-in-costa-rica-thin-oil-bros-continue-at-your-own-risk.408318/

 

[tired]

Yes, it should because those temps. affect the optimum engine cooling. It causes stress on the cooling system (water pump, thermostat, radiator fan) and hence the oil system too. Check this thread out:
https://bobistheoilguy.com/forums/threads/stopped-by-an-auto-parts-store-in-costa-rica-thin-oil-bros-continue-at-your-own-risk.408318/

There's nothing in that thread about weather and grade. They don't have CAFE in Costa Rica so there's no need for 20 grade or lower oils there.

 

[Japanese]

There's nothing in that thread about weather and grade. They don't have CAFE in Costa Rica so there's no need for 20 grade or lower oils there.

Exactly!
Plus they run older cars and 20W-50 grade is one of the easiest to produce, I guess.