Not true. I'm my 2014 Mazda3, if I'm not using CC and coast down a hill, the current mpg pegs 99.9. With CC ON (@60 mph), going down that same hill, current mpg hovers goes from about 30 to 35 to 45 and maxes at about 75-80. Same applies elsewhere: on less hilly roads, if I accelerate (gradually) and let it coast on the downward stretches, I go from between 30 - 50 (up) and coast at 99.9 down; however, with CC ON, I get about the same on the "up" but between 30 and 60 on the downslopes.

This is consistent.

 

I spoke with a 50-something (no rookie) mazda tech who trains dealer mechanics at conferences. He said there is no traditional break-in period as there was 5-10 years ago. While they do recommend driving "gently" for the first 600-1000 miles, he was absolutely adamant that there is no "break-in" period associated with the car "learning" and/or "adjusting" in any way, shape, or form that would result in increased fuel economy over time.

As for the fuel system cleaner, which bottle did you pull those marketing bullet points from?

 

See post 5. Redline is a quality cleaner.
Cleaners do work.
Ever try lacquer thinner in your fuel tank? It does wonders for catalytic converters and O2 sensors. I've done it as well as Tanprotege with amazing results. My car runs better now than new.

"While they do recommend driving "gently" for the first 600-1000 miles, he was absolutely adamant that there is no "break-in" period associated with the car "learning" and/or "adjusting" in any way, shape, or form that would result in increased fuel economy over time." -------- This is contradictory, drive it easy to get computer used to your climate, driving or whatever yet has no effect on mileage is ridiculous. This is how politicians talk - he is a speaker?.

If I was that conscious about fuel mileage, i'd have bought a hybrid. Fuel economy is measured under controlled conditions in a laboratory using a standardized test procedure specified by federal law. Manufacturers test their own vehicles—usually pre-production prototypes—and report the results to EPA.

 

I've had 3 fill ups with my 2.5l sTouring sedan so far.

1st fill up I had a ton of idle time sitting in the car playing with features. I got 21mpg.
2nd fill up I went on a cruise with the local Mazda club and was driving in sport and manual modes the whole time driving very enthusiastically. I got 23.9mpg.
3rd fill up I drove normally and took it very easy and relaxed and avoided any sort of idling except when in traffic. I got 32.2mpg.

 

I am a proud new owner of a 2014 Mazda 3 also.I am in Los Angeles and have just hit about 1300 miles but yesterday I noticed that the fuel eco on my 2.5 liter was locked at 33.8 mpg current with cruise control set at 73 mph .and it would not budge for miles along the 91freeway at 1am light traffic. that day I drove over 200 miles. and noticed previously to this day I was getting 38 and sometimes 40 mpg on cruise set at the same sort of levels. Today this concerns me abit as this is a brand new car that suddenly stop performing at optimal levels as the days before.Now with all this over kill technolgy regulating this and that I am worried that something may have (god forbid shorted or glitched) . Of course the car is under warranty but still! its brand new.. so I did this day have to refuel two times and saw my fuel gauge drop dramatically.What changed or what I did do diferently that may have cause this bad gas mailage issue was:
This day the temperature was cold 58degrees outside
I Drove quite a few times very hard in sport mode with paddle shifters mashing
ripping through traffic avoiding danger (oh how I love the torque and driver connection).
but i always switch back to normal when cruising to conserv fuel on freeway stretches.
Now what I think is happening is the Sport mode might be still ingaged even though I turned it off or something else has gone wrong?
I will look further into this and if this continues to get the 33 mpg locked milage I will goto the dealer and have them diagnose the system.
I am thinking it could be the cold air and the slight grade from the coast to orange county inland on 91 ?
but all I know is I refueled way too much that day and from what the gauges where telling me seemed very off in some way.

 

All of your suggestions are true in neglecting mileage:
1) jack rabbit take offs --- Quick acceleration and heavy braking can reduce fuel economy by up to 33 percent on the highway and 5 percent around town.
2) colder air (although 58 may not be that cold, but winter time is poor mileage) ---- when it's colder outside it takes longer for your car to warm up --- during this period the ecu gives it more fuel to warm up. This cold air intake vrs gas mileage is very complex because of the denser air (more oxygen). Changing the density or temperature of the air will be accounted for by the computer to maintain a stoichiometric mixture that is ideal for the catalytic converter's operation. The final control is the closed-loop feedback system, wherein the oxygen content of the exhaust gas determines fuel delivery. The ideal air-to-fuel ratio for optimum emissions, fuel economy and good engine performance is 14.64 pounds of air to 1.00 pound of fuel. This ratio is referred to as the stoichiometric mixture.
3) incline -- Driving on hilly or mountainous terrain or on unpaved roads can reduce fuel economy. The EPA test assumes vehicles operate on flat ground.

Personally, I love my CAI (which is also a SRI) because of the sound and the power due to the density. It does not lag in hot humid days around town! Hot intake air from under the hood is a no no.

 

I still haven't gotten the answer I'd hoped for but there are so many thoughtful contributions, I thought I'd try to ask in another way...

First, my last car, which I bought used, was a 2006 Altima. In the week after I bought it, I was interested to see what mileage I was getting. I was getting 24-25 mpg. I thought: that's cool. I never thought about it again.


When I got the new car S Grand Touring hatch, the computer said it had been getting 26, still on the low side. Right now, I'm working from home. And I play music but in local clubs within 20 mins of where I live. I'm doing most of my driving in thickly settled areas (30 mph limit), and since getting it, I've put on 500 miles. I'm in my 40s and not drag racing. I've used the sport mode a number of times but not the shifters. According to the computer, I'm getting 17-19 mpg, averaging only 15 mph. Ive confirmed the mileage with a manual test So my question was really was: can the driving conditions and my driving manner, in and of themselves, drag down fuel economy that drastically (35-40%)? or is that impossible, and something more significant likely going on? Having polled others, so far it seems like lots of people believe that it could be the case and not to worry. But I have not heard an answer from a mechanic.

 

here is an update of my situation. The next day the temperature was above 60 degees at 62 as I made the same drive from LA on 91. but this day the car seemed back to complete normal giving me 40.1 mpg ; however i was driving with CC on at 69 mph. but the car was running perfect and getting great mpg milage.I believe the system reset overnight and that it is back to normal for now and maybe the fact i kept it at 70 and under helped? Well for now seem good. , I will keep you all posted.

 

Just to add another data point, my i GT (2.0L) is giving me an average of 36.0mpg after 2500 miles driven, which is about 60% highway, 20% rural (low speed but no stop-n-go), and 20% city stop-n-go. That seems spot on according to its rating. I go easy on the accelerator and try to keep it around 65-70 on the highway.

I thought cold weather was supposed to increase mileage, not decrease, because A) cold air and gas are denser which increases the compression ratio, and B) given equal volume, a gallon of cold gasoline is denser (more energy) than a gallon of warm gas. Plus you are likely keeping your windows closed and using heat (free) instead of A/C which takes energy.

 

Listen to this video.
Especially @ 2:06. ECU compensates for denser air by adding fuel giving power. This is a controversial topic, especially with ECU's and it's a topic we should avoid.
When it's colder outside it takes longer for your car to warm up --- during this period the ecu gives it more fuel to warm up affecting overall mpg on the trip. This cold air intake vrs gas mileage is very complex because of the denser air (more oxygen). Changing the density or temperature of the air will be accounted for by the computer to maintain a stoichiometric mixture that is ideal for the catalytic converter's operation. The final control is the closed-loop feedback system, wherein the oxygen content of the exhaust gas determines fuel delivery. The ideal air-to-fuel ratio for optimum emissions, fuel economy and good engine performance is 14.64 pounds of air to 1.00 pound of fuel. This ratio is referred to as the stoichiometric mixture.

Trust me when I say the SRI will not give you more power as it sucks in the hot air from the engine compartment --- you need to install a baffle to suck in air from outside for maximum benefit-----like i did.

The long CAI intake is not great to due water splashing on the filter as you go through a car wash, puddles. Plus it's a longer tube. Shorter is better to a point. You need a perfect balance between short and getting at cold air, of which i accomplished for maximum zoom zoom! Who cares about mileage, it's about the zoom zoom.