Sounds counter intuitive but seems like I'm getting less MPG after switching from dino to synthetic Mobil One Extended. These MPG readings are from the car's trip computer.

Could this be true? And if so, why?

Thanks.

Unlikely. Short term comparisons are very difficult because there are SO many variables. Assuming you are running the same viscosity as you were with dino - there is nothing inherent about syn that would make an engine less efficient.

yup 5w30 will give slightly better mpg then 10w30