Questions regarding 0w40 oil

[jhonz1981]

Originally Posted by tmontague

Yes, your mileage will go down as your operating temp oil weight is going from a 40 to 50. It shouldnt hurt your fuel efficiency a ton, but it will have a negative impact.

Why the heck would you want to run a 10w50 in the 1nz? Even with 300* oil temps you would be way out of oil pressure spec and have potential flow issues. On top of that your oil temps would be much higher

Thanks tmontague for your reply. Would like to clarify that 10W50 is only a scenario. My yaris (1.5L 1NZ Auto Trans) is currently used Toyota recommended 5W30 oil since the 5W40 (used up to 20k kms) is not available anymore in the dealership.

So, what engine oil grade would you recommend for summer and heavy traffic situations that will increase fuel efficiency and protecting the engine? The car is 3yo and 52k in its odo. Just like Bony_ahmed Im considering to switch to 0W40 if it is safe and can satisfy those aims.

thanks a lot in advance.