i have a corolla 1.3 gli 2011 65000km. i have been using pso carient 20w50 oil for the past 2 years. for my latest oil change, i got caltex havoline 10w30. is this oil good for summers in lahore with temp around 50c? should i stick to 10w30 or should i get havoline fully synthetic 5w30? i change the oil after 5k kms. do u recommend a better brand/oil?