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2010 Mazda 3S 5-Door getting crappy gas mileage...and I'm not just saying this because of gas prices

So I owned an FJ Cruiser for a while and decided to downsize in an attempt to save on gas. The FJ was great and served it’s purpose, but I bought a 2010 Mazda 3 Sport 5-Door last year for various reasons.

From the day I started driving the car the average MPG on the dashboard meter seemed low. I thought to myself, “Give it time…maybe it needs a solid 1k miles or so before it’s accurate”. Then I started checking the mileage at fill-ups manually. I found I was only getting 19-21 MPG on the HIGHWAY!!! Only 18-19 MPG IN THE CITY!!! Horrible. The sticker claims something like 28-29 on the highway and 22-24 or so in the city.

So I took it in to the Mazda dealership for an oil change and told them to check the “codes” to see if they could find anything related to the poor gas mileage. They called me the next day and said, “No error codes are present, therefore we can not do anything about it.” The only other option was to have one of their techs borrow the car for a few days to see what kind of gas mileage they get in it…somewhat assuming I had a lead foot. They also blamed the bike roof rack I had installed on the vehicle which is a Mazda OEM part. :frowning:

So needless to say I gave up on the service dept at the dealership I purchased it from and found that many other Mazda owners are reporting the same problem on various Mazda forums; while others are reporting the actual mileage that is claimed on the sticker or better.

I won’t lie to you and say I’m easy on the pedal, but I don’t drive like a bat out of hell either. I go 5-10 MPH over the posted speed limit anywhere I’m at. In my opinion, the roof rack is in no way hurting my gas mileage enough to be of concern…maybe 1 MPG or something (in fact I noticed no difference in the first few months I drove it sans rack). I’ve checked the mileage manually and with the Avg. MPG meter installed on the dash and both are accurate. All service has been performed by the Mazda techs at the dealership and no codes are apparent so Mazda refuses to do anything about it.

Does anyone have any clue as to why I’m seeing such a huge difference in mileage? Any diagnostics I can run on it myself or things I might check?

FYI, it’s the 2.5 Sport model, 5 Door and it’s an automatic.

Thanks so much!!!

Eric B.

Your car is getting the fuel economy that it was designed to get. Those stickers are for the base model which does get the fuel economy listed. The speed sport is rated at 26 MPG overall, so there is hope. The new cars I have driven took 3,000 miles before the fuel economy became OK. Still there is hope, you just have to wait.

You lose fuel economy because of the bike rack. Just look at how clean the body style is and then imagine how bad it gets with a roof rack. You would be lucky not to lose 2 MPG with one of those things.

If you’re driving 10 MPH over the limit before 3,000 miles, you won’t see better fuel economy until you get to that figure and drive slower. No matter how you drive, it would be a miracle if you got 28 highway MPG. If that happens, feel free to send a donation to the charity of your choice because somebody is looking out for you.

How are you DRIVING the car?? How you drive is going to be the BIGGEST factor in gas mileage.

Do you do quick fast starts or more of a steady increase??? Drive 20-30mph over the speed limit??? Wait till the last minute to brake…then brake hard???

One of these magazine shows did a test…took two identical vehicles but with two completely different drivers…The driver who was much more conservative…got almost twice the gas mileage as the aggressive driver.

That is pretty crappy mileage for a Mazda3. Are the tires correctly inflated? You don’t have the OD turned off, do you?

The Driver Has Already Stated, “I won’t lie to you and say I’m easy on the pedal, but I don’t drive like a bat out of hell either. I go 5-10 MPH over the posted speed limit anywhere I’m at.”

If I’m not mistaken this is the sportier version of the car and it is made to dart around in. My Bonneville gets better mileage, no matter how I drive it.


Check the wheel alignment.
Does the temp gauge come up to normal promptly? (in a couple of miles in the summer)

Here’s the real question:

Exactly how FAST are you driving the car on the highway?
If you are only getting 22 mph while at 55 mph, then something is wrong with the car.
If you are getting 22 mpg at 85 mph, with a bike rack on the car, then that probably is normal.

The gear ratio for the final drive is fairly high at 3.65:1.
This means that the engine rpms are going to be fairly high at high vehicle speeds in top gear.

Are you able to feel the transmission shift through all 5 speeds?
Hopefully you don’t have the o/d turned off (something my sisters and my gf’s daughter do all the time, and then complain about poor fuel economy to me).


The other question is if these are truly highway miles or simply congested freeway miles?

I know too many people who complain about highway mpg when they sit in bumper-to-bumper rush hour traffic going at a crawl for their whole commute… somehow they think there’s something magical about the road surface that should give them better mpg. Not saying the OP is one of these, but it is a question I often have to ask…

How are you measuring your fuel mileage? Are you going solely on the computer, or are you filling your tank(make sure you don’t fill it anymore after the pump clicks off), then taking miles driven divided by gallons used?

To answer your questions:

  • I do NOT HAVE the Speed Sport. If so I’d be tickled pink to get this mileage. I have the Sport version of the Mazda 3 which basically just adds bluetooth, a spoiler and different interior.

  • the roof rack does not hurt the mileage as much as some are stating. I was getting the same mileage BEFORE i had the rack installed.

  • The miles are true highway miles…non congested freeway miles.

  • I’m manually checking the mileage at the pump with my calculator, and using the onboard computer. Both are spot on.

  • There are times I take off from a start fast, but most of the time I’m not acting like I’m in a race.

I do feel the transmission through all gears too. Overdrive is working, I don’t think I can shut it off if I wanted to.

On the HWY, I drive it 75mph, speed limit is 70. From my checks on the mileage the roof rack did not hurt the mileage by any noticeable amount. Maybe 1mpg difference.

The wheel alignment should be good…they were supposed to check that last time I took it in. I wouldn’t know how to check this myself unfortunately. Funny thing is that the Mazda 3 does not have a temp gauge…not that I have seen anyway. There might be a light that kicks on if it gets too hot but thankfully I haven’t seen that either.

Finally I’m over the 3,000 mark and it seems it’s worse than ever on mileage.

I asked about the temperature because I was thinking about the thermostat.
A stuck thermostat could keep the engine from warming up fully and kill MPG.
At 3000 miles a very early failure or bad from the start.

A quick, easy check:
Start the engine up cold, let it idle and feel the radiator hoses for a few minutes.
Very little or no hot water should go through the hoses until the engine is warmed up.

I would next get the engine temperature sensor(s) tested.
Measure engine temp with a laser thermometer.

Try this, take it on a lonely road, and at 25 mph, slip it into neutral and see how far it coasts. It should coast for about a 1/4 mile on level ground before rolling to a stop. If it is significantly less than this, then I’d suspect excess drag somewhere.