in this harsh weather with AC running Petromin ultra 7, 20w50 is best, cost=1600
You can also use good brands like Castrol GTX 20w50
or Havoline 20w50
However these brands have lower oil spaecs as per new cars after 1997
if you are using a thin oil already then good brands are
Mobil 15w40, Rs 1900-2000
Castrol magnatec, 10w40
liqui moly15w40
if you ve been using synthetic oil till now then nothing works better than Mobil1 ( the best oil in the world)(H)