Well then, as an engineer I have to say I disagree with you both. Just because there are no (or precious few) shavings to be dealt with in modern engines does not in any way mean that certain components (thinking cam lobes and the ring/wall interface here) cannot benefit from an initial dose of certain additives. Funny thing, that's exactly what the engineers I worked with at Mercedes told me. Of course Nuburginger thinks they were pulling my leg, and I of course think otherwise.

After 7 months of driving my Mazda5. My average mpg is between 21mpg to 25mpg. I once got 27mpg when I tried to drive it extremely easy on the gas pedal and brakes.

Automatic transmission I presume.

1st tank...
 

Yes my Mazda5 is automatic. I'm not sure how much difference a manual Mazda 5 touring can get in real world driving.

There have been a number of posts on this board from Mazda5 owners with manual transmissions which report highway mileage of low to mid thirties.

I have a little over 8000 mi on my 2012 5 Touring and am a little disappointed in my average MPG. I split pretty close to 50/50 city/hwy driving and am averaging around 22.8 MPG. Took it for a 410 mile trip (one way) a couple months after I purchased it and still only averaged 24 MPG. Granted, that was doing just a "tad" over the posted limits in places, but....

Automatic transmission or manual?

2011 Mazda 3 Touring 2.5 4cyl........On my first full tank 95% highway driving on premium gas I hit 32mpg. Amazing I was not expecting that at all. But I did get it.

Stop using Premium fuel, your engine wasn't designed for it and as such, you'll see slightly reduced fuel economy and power by using it; not to mention the likelihood of increased combustion chamber deposits.