What about winter, when temp. outside drops to -15°C or so? Is 0W-20 or 5W-30 a better choice?
0W 20 is clearly better for a cold engine start in winter for the same reason it has better fuel economy. It is simply thinner when cold on engine start and thinner at low operating temps which is ideal for the hybrid engine. Obviously this doesn't mean all 0W 20 have the same viscosity at low temps. If you start comparing the viscosity of different 0w 20 oils you will see that Toyota's oil is about 30% thinner at 40 degrees than a common 5w 30 (i.e. valvoline). It is the only 0w 20 oil with a viscosity index higher than 200 and the only alternative that comes close is Mobil 1 (btw they make the Toyota oil in the US). Both oils have been scrutinised a lot in oil forums and oil analysis tests and everyone is happy. Therefore Mobil 1 0w 20 is the only other alternative i would consider.
For the 1.2 turbo engine i haven't seen what the manual says and i can't comment on that but as the engine works at normal operating temperature and it has a turbocharger i might consider a thicker oil to handle the higher operating temperatures compared to the hybrid. Unless of course the car is used in a really cold country where cold start is more important for someone and the car doesn't do any racing.
Very informative answer, cheers.
Just to say also that, according to an email i sent some time ago to Toyota head offices, they said that "5w30 is also satisfied oil according to the owners manual".
Also, wanted to ask you, as the 0w20 oil they use is Toyotas oil, i guess also the 5w30 is Toyotas ? Not something else, like mobil etc, correct ?