20w-50 should not be used with this engine,
5w-30 or 5w-40 and 10w-30 are fine.
regarding 5w-20 i think its also okay to use as it is recommended by toyota japan for use in vitz with same engine for less noise and better fuel economy. but i think it shouldn't be used in extreme hot weather(like for next 2,3 months). experts can explain better.