5W-20 is recommended for all newer cars. I have been using it in My Nissan with swapped engine for last 2 years, and no problems at all, even in hottest months of June-July on long routes.
I was getting fuel economy of 12 kpl on long before installing thermostat and switching to 5W-20 from 10W-40. Now getting 16kpl.
Don't know whether t-stat made this much difference or oil had some impact.
But as per my study, all vehicle manufacturers are shifting to full synthetic 5W-20 or max 5W-30.