Synthetic oil MPG boost since change

[alhope34]

I use 5W-30 Mobil1 synthetic with the normal Toyota oil filters. I never bothered to see if there was a mpg difference when I changed from normal to synthetic, it was around 3000kms on the car. I was just interested in the added engine life that comes along with using a full synthetic constantly since after break-in. I try to change the oil between 6-8000kms, and the oil is usually not too dirty. Not amber but not complete black like the cars we'd get in at the dealership.

Personally, I'd be kind of iffy using a 0w-30 oil. At the Toyota dealership when I worked there they were dead set on 5W-30 for all their cars. Didn't matter if it was synthetic or normal, even if customers bought their oil somewhere else, we would only use 5W-30 unless the customer absolutely insisted on other type. Would that have something to do with the oil pump pressure? Could the lighter oil mess it up somehow? I know using a thicker oil isn't good as it restricts oil flow, especially during warm up.