Mazda 3 2.3 liter gas mileage

[auzoom79]

Hey guys, I know there have probably been multiple threads over time on this, but just fishing for some generic info. I recently lost my Mazda 6 due to a meeting it had with a center guard rail. It was a 2005 with ~75k miles and the 2.3 liter engine, 5 speed. I now have a 2004 Mazda 3 with ~47k miles and the 2.3 liter enginer, 4AT. I was getting dead on 29-29.5 MPG with my 6 with about 90Hwy/10City driving. I am only getting about 26.5 MPG with my 3...what gives!?!? I would have thought my MPG would improve on the 3 vs the 6, but it has been opposite. I have tried running premium gas and regular gas but don't see much difference. I have ran a few tanks with Chevron fuel injector cleaner, but doesn't seem to help. I have ordered an EGR valve to see if replacing it may help (thinking the old one may be stuck open). Any other ideas why the MPG would be worse on the 3??? Thanks!!

 

[weatherdan822]

It's that extra gear you had in the 6 that helped with the fuel economy, so at 65mph you were most likely pushing 2500 on the tach while in your 3 you're engine is turning at around 3000. 1 freaking gear haha! It's that reason why I wish I had an '05 3 vs. my '04 3.

 

[auzoom79]

I actually tach pretty much the same. Both tach about 3000 at 65. I think the 4AT does have an overdrive (once in 4th it will shift one more time and the rpms drop by a few hundred. Can't read anywhere about an overdrive of any kind but I know it will shift once more after it's in 4th gear. I just can't understand the difference in MPG between te two cars with the same engine when the 6 is heavier but gets better MPG....

 

[weatherdan822]

Yea, I understand what you're saying; you do bring up a very good point nonetheless. Now you've sparked my curiosity haha.

 

[Magus]

Mazda 3 hatchback Coefficient of drag: 0.33
Mazda 3 curb weight (lbs) 2,857lbs
Mazda 3 0-60: 8.0sec
-these specs with 4AT

Mazda 6 Coefficient of drag: 0.27
Mazda 6 curb weight (lbs) 3241-3311 lbs
Mazda 6 0-60: 8.0sec

If I was doing the ratio you are with my newly acquired 2005 Mazda 3S Touring manual I would be getting 29mpg. Right now with a need for oil change, spark plugs, pcv, transmissions flush, and winter gas I am getting 26.5 mpg. Mind you I am doing 70/30 lately because of construction.

 

[auzoom79]

Thanks for the numbers Magus. I am hoping I may have found the issue. I had noticed a much larger amount of brake dust collecting on the rear wheels compared to the front. Usually the opposite would be the case. I had at first chalked it up to the front pads being replaced by the PO and the rear pads being original hence more dust. I also had a roar that changed with speed. When I had the tires rotated I noticed the right front was cupping, so I thought the roar was just from the cupping. Well, I changed the rear brake pads this past weekend and guess what I found....both rear wheel bearings were gone! I have immediately noticed a much quieter ride (wheel bearing were making the majority of the roar - just a little remains with the cupped tire). I think the wheel bearings were doing two things - causing more friction -> less MPG and allowing the brake pads to excessively rub the rotor -> more friction -> less MPG. I will try to remember to post results once I run the next full tank of gas. I suspect it should get better....we'll see...

 

[Magus]

auzoom79,
Definitely every bit counts! I would also check the brake calipers to make sure they are sliding properly. If the brake caliper is not working right, that too would kill mpg and cause extra brake dust.

 

[Magus]

My mix has changed, plus the oil (90/10). I am now getting 27.8-28 mpg and I think I can get a little more as the spark plugs are due, I need an alignment and I think my front struts needs replacing.

 

[MazdaBoy234]

My 07' 2.3 is getting between 27-28 during the winter with about 70/30 split on highway/not driving.

 

[bbrich57]

I have an '04 3 5Dr, 2.3L, but I have the 5-sp. I do mostly city/city like driving, and the same route most of the time too.
26-27mpg if my foot is in it a lot, or I run the revs up. Or have a lot of stupid stop/start drivers in front of me.
28-29 is normal if traffic is reasonably good that week.
I just filled up this morning. A check indicates 28.41 mpg for the past 10 days.

It's got to be the 4-sp slushbox you have causing the mileage issue.

 

[Gibbsinator]

IMO the combination between 4 spd and Automatic is your problem. AT is losing out on about 8hp more then MT is. The more I drive my car the more I'm glad it's a MT.

Check your Air filter, if it's dirty it could be restricting air and that will easily lower efficiency. Do you use cruise control? If you have it I would try it.

 

[Magus]

I would also check your spark plugs depending on age, and check your psi in your tires.

 

[auzoom79]

Hey guys, just a quick update. I changed out the intake to a Mazdaspeed CAI, cleaned out the throttle body, and cleaned the MAF sensor. I have now been through 4 tanks and am averaging 29 MPG. I had previously replaced the spark plugs which didn't seem to help and I make sure air pressure is good (34 front, 32 rear). It seems the intake and cleaning the throttle body and MAF sensor did the trick. I am very happy to be averaging 29MPG now. I think if I were to go on a long road trip with all highway I could get 30+. Thanks all!!

 

[Baundiesel]

'08 auto 2.3, I get about 25mpg on 60/40 city/highway driving.

 

[adumbrille]

2007 2.3 with intake/throttle body/exhaust/header/intake manifold/hypertech and I get 29 mpg mixed. I closed my spark plugs to .046 (factory spec is .050 to .053) and gained some mpg's.

 

[Scythe]

I know I'm here a years later but I have 05 MZ3 2.3L, Just curious are you guys using OEM spark plugs? If not any suggestion on what could be better for our 3's.

Thanks