My corolla is up for an oil change soon and im planning to shift to the thinnest possible oil which is 10w-30. I checked the manual and 5w-30 is rated only for use in extremely cold weather (below 0). Engine is the 2E carburated one.

1.) is it to switch to 10w-30 oil, im currently on 15w-40? (not sure kung yun yung specs ng oil pero I use the yellow shell helix)

2.) can anyone suggest a good brand and estimated market price?

3.) is 10w-30 fully synthetic or semi-synthethic?

salamat marami.