[davehasl]

2019 CX-3 Sport, 30k miles, car purchased March 2022, certified pre-owned from Mazda dealer

My driving is mixed, 50 - 60% freeway. I measure fuel economy by using the range estimate -
when it gets down to 15 miles remaining, I make note of the miles I did since I last filled it up,
I've been getting 330 - 335 for the last few months (since I ran a bottle of Techron through the fuel system)

But the last two tank fulls have seen the gas mileage drop by about 10%.
It may be a coincidence, but just prior to this the car did something unexpected,
I was doing about 55 - 60, slight incline on the freeway. I gave it some gas, and I think the
engine dropped into second gear - the revs momentarily increased to 5 - 6000 revs.

I was surprised the engine management would do this. The transmission was in regular "drive",
I did not floor the gas pedal.

Except for a worse fuel economy, car seems to be OK I'm due for my second service early February

Any thoughts appreciated

 

[Malks]

There are plenty of things that effect fuel economy, a big one is temperature. I'm not sure if it gets cold (below freezing) where you live, but if it does that alone could make up for the 10% drop. Higher revs on the engine will also increase your fuel consumption, but most of the time while using the fully automatic shifting the transmission will do short shifts (earlier upshifts well before the peak power), just to keep the revs lower for the best economy.

When you hit the gas pedal on the uphill section the car probably shifted down to 3rd; 2nd might have been a little too low if you were travelling at 55 mph. With a 6500 RPM redline you were close to that, but still within the safe range. I'm sure the car upshifted quickly out of that gear once you began to accelerate.

My AWD GT model has the display that shows distance to empty, so I don't have to do the math on every tank full. I've recently noticed that the computer has been reducing the estimated distance as the weather gets colder. I've also been driving more in town, which is another negative factor. In the summer the display will usually show just over 500 km (310 miles) for a full tank, but lately it's only been around 450 km (280 mile) range. Apparently you get better mileage on your CX3 than I do at the best of times. If your car is FWD that could explain some of the difference. Driving styles also play a part and I tend to like to use the paddle shifters on my car while driving on snow covered roads just because it's so much fun!

Enjoy your CX3, I also bought mine as certified pre-owned from a Mazda dealer and have had it now for three years. I absolutely love it!

 

[hsdejong]

In the summer the display will usually show just over 500 km (310 miles) for a full tank, but lately it's only been around 450 km (280 mile) range.

My display (CX-3 with Front Wheel Drive, Cylinder Deactivation and Manual Transmission) shows between 750 and 800 Km (470 - 500 Miles) with a full tank.

Am I missing anything besides driving style?

 

[Malks]

My display (CX-3 with Front Wheel Drive, Cylinder Deactivation and Manual Transmission) shows between 750 and 800 Km (470 - 500 Miles) with a full tank.

Am I missing anything besides driving style?

First of all wow on the mileage of your CX3! I have never seen a number larger than 550 km on my distance to empty display and that includes a 4000+ km road trip from Ontario Canada to Florida USA this past April.

I know that the fuel tank on the AWD is shaped differently because of the driveline, so it might have slightly less capacity. My AWD also would not be as fuel efficient as your FWD model; additionally mine has an automatic transmission, which is less efficient than a standard trans. While my CX doesn't have the cylinder deactivation, that is really only a benefit for stop and go city driving, which I don't do since I'm retired and live in a small town.

An average of 750 km on a tank is impressive!

 

[hsdejong]

I know that the fuel tank on the AWD is shaped differently because of the driveline, so it might have slightly less capacity.

The fuel tank size in the FWD CX-3 is 48 litres and if I am correct the size in the AWD model is 44 litres.
That means that with a 44 liter tank the display would indicate a distance of (44 / 48 x 750 to 800) 690 to 730 km.

 

[davehasl]

Thanks for the feedback. The most mileage I ever reveived since I had the car is 335 (536 Km) using the method
I mentioned in the top post. At my first oil change the service guys tried to sell me the gas service they do
which I declined at the time but may reconsider in February. According to info I've seen the expected mileage
for this vehicle is 29-33 per gallon
I'm in Los Angeles, so ambient temps 55-65 F this time of year.

Yesterday took a short trip on the freeway, traffic mostly clear, left the car in "Sport" mode; got up to about 5000 revs.
(momentarily at about 80MPH)
The note of the engine did not seem as high as in the incident I mentioned above.

Likewise, myself and family are really enjoying this car, very pleased with the purchase

 

[Malks]

The fuel tank size in the FWD CX-3 is 48 litres and if I am correct the size in the AWD model is 44 litres.
That means that with a 44 liter tank the display would indicate a distance of (44 / 48 x 750 to 800) 690 to 730 km.

Yeah, I'm not getting that kind of mileage on my AWD model. As I said, the highest number I recall seeing indicated for range is around 550 km; I've never seen anything over 600 km on the display.

I'm quite pleased with the mileage my CX3 provides and have never really tried to keep track of the fuel used for distance travelled. Although I did keep track of the cost of fuel for our trip to Orlando in April 2022. On that trip we used US$330 in fuel when the price was just over US$4 per US gallon. I was quite happy with that cost for the trip as opposed to well over CDN$1500 for us to fly there and back.

 

[Zechariah936]

There's other posts in the forum, with peoples fuel range. Personally I get 690Km - 750km.
Mixed city driving with some freeway driving. I don't drive conservatively, thats why I have a manual, zoom zoom.

All the comments above are accurate, temprature, altitude, tyre pressure, engine revs, load etc etc all make a difference. However it should not be huge (eg for me, tyre pressure 2.2KPa all around = 6.2L/100Km VS 2.4KPa all around = 5.8L/100Km), this is not going to break the bank, and again it's average. Short trips this wont affect my life, long distance it will add up.
So if you consider all the variables that you can control, then it may make a difference and be worth testing.
Regular maintenance, fuel system cleaner, 95 Octane or higher fuel, correct tyre pressure (considering load & rating), most importantly driving style (consistently braking and slowing down then having to rev up again, constantly over rev etc)

FYI I drive with 2.3Kpa tyre pressure - comfort and economy for the tyres I have now Primacy 4plus.
Fun Fact: lowest average consumption: 5.5L/100km.

 

[Tomypop]

Here are some the main causes for a sudden drop in gas mileage: Bad oxygen sensor and air filters-in all forms will affect the fuel mixture and your fuel efficiency. Bad or misfiring spark plugs-will result in poor performance and subsequent lack of power will cost you fuel efficiency.

 

[davehasl]

I switched to mobil gas for just one tank and saw approx 7% fuel increase; I've since filled up with Costco's gas
again but will repeat the experiment later this month.
With the mobil gas I received 345 miles driven when the display on the dashboard told me I had 15 miles remaining.
Also, I used the app in the computer and received 32.8 average over the tankfull, mixed driving. Prior average
was 28.4 (Costco gas, many tankfulls).
Not too bad, but not as much as some of the previous posters.
I have found the tire pressures to be critical on this car, more than I've noticed on any car previously,
it feels terrible if it's just a pound or two above or below the recommended. Feels like it's on rails
I have a service appt. this month, they want to do do the fuel injector/system flush and change the air filter.
We'll see.