My personal experience :
I started research on changing of oil viscosity for my GLI 2009 having done 85k at that time around 10 months back.
I contacted liqui moly Germany famous brand oil senior representative and discuss with him on email that I need to change the oil viscosity of my car.
These bloody Toyota 3s are totally playing with the innocent customers because mostly people just know that they have to change oil at specific kms. Which oil is good for their cars, only very less people know.
I was interested in liqui moly 5w40,
However that senior rep also told me that make sure your car engine seals are good, not having any leakage issue also the engine is not consuming oil.
So, for an experiment I put Mobil 10w40 in my car after that Toyota petron 20w50.
Results were great, I felt the car is lighter, more pic more mileage.
I am using mobil 10w40 from last six to seven oil changes and it's perfectly fine.
For newer cars you should put thinner oils like 5w50,5w40,5w30....
Dont put 20w50 in your new car... It will ruin the engine.
Just imagine in winter, u start Ur car and engine is still not fully lubricated because 20w50 is a highly viscous oil.
More wear and tear will take place.
Use original Toyota oil filter.