Firstly a big thank to the gentleman who sent me complete manual of Toyota Passo by email. Am really thank full to him.
Here is what they recommend in the manual.
1KR-FE (1000 CC engine) 0W-20
1NR-FE (1300 CC engine) 5W-30
They repeatedly mentioned in the manual that for "BEST FUEL CONSUMPTION" feed 1KR-FE with 0/20 oil. it will give the best mileage.
I know hundreds of Vitz are out there and people are pouring 20/50 oil and changing after 3K.
Moreover I've checked with LM's head office in Germany and here is the min. & max. range of the oils we can feed to 1KR-FE.
These cars will ideally work in above oil range.
So technically these engines will "not work ideally" if we will feed them 10/30, 10/40, 15/40, 20/50 etc. oils.
Presently Kixx G1 (Tin pack) is 0/20. Price 2800/4L. SCI is 5~6K. Just forget either its summer or winter, if you want to save on fuel consumption, then 0/20 is the best choice.
If anyone need the manual, write your email here. Its 8MB file and I'll send once to all.