Why is my mpg falling?

[minimo3]

This is a 2011 7-speed model. The car is driven mostly on suburban roads (no lead footed driving, averaging around 40mph with some traffic lights some stop and go). I measure mpg by resetting the mileage counter on each fill up and dividing by the gallons used to fill it up. When we first got the car it was getting around 19mpg. Over time it went down to 18, then 17, and on my most recent fill up it was about 15mpg. Is it the winter blend? This is the opposite of what I've experienced with my other cars where mileage improved as the engine was broken in.

[costa_rican13]

hows you're maintance on the car? change the air filter? oil? tier pressure checked? driving the same and non-spirited?

[jmann]

Gas mileage always gets worse in cold weather due to winter blends as you mentioned and the fact that the cold air is denser, so your car uses more fuel to correct the a/f ratio. The plus side is that you get more power for the same reason.

[minimo3]

Its been maintained according to Infiniti's schedule - sent to the dealer every 3750 miles. Tire pressure is set to 33psi all around. Driving style is best characterized as "little old lady" style; the engine never even revs above 3000rpm.

[costa_rican13]

gotcha, also what imann says is true as well. so only a couple a mpg's isnt really something worry about although kind of an inconvenience.

[sashki2]

In my case, once I got used to the car (or simply my mood changed?), started driving a bit more aggressivly - the fuell economy went down 2-3 mpg

[XIS]

I got mine with 30K on it and my first tank was 18mpg, then 19, eventually it was closer to 20 and my last tank was 21.1 !
(21.1 was my calculation (miles/gallons)) The car said it was 21.4. Pretty darn close and very good~!
By comparison, my RDX's computer always showed 1.0 - 1.5mpg better than actual. Pretty weak. That powerful 4 cyl only got 16.5 to 17.5 actual MPG...but the more powerful EX35 V6 is getting me about 3mpg more with the same driving style.

[XIS]

Sorry - hit submit too early...
Your issue is probably affected by the a/f mixture, but I am not sure where you are from. Also - how many miles do you have? Do you drive in town, small streets and stop and go, or do you drive several miles at a time on a HWY? Is there snow involved? Is there a longer warm-up time needed due to the weather?

Here in the desert, MPG goes UP in the winter months because we are not using our A/C , and driving between 60f and 80f seems to be a sweet spot!

[minimo3]

I'm in the New England area. Temps are around 45-60 F currently. The car is still fairly new with about 7000 miles on it. Driven mostly on suburban roads. There is some stop and go in the mornings on the way to the office but its smooth sailing on the ride back in the evening. Speeds rarely exceed 45mph. Distances are fairly short, about 8-10 miles each way. Its my wife's car really, I'm more of a Mazda person.

[NJGuy]

In addition to winter blend fuel, I'd say that the colder outdoor temperatures require longer warmup times for your car when compared to the summer. Colder engines run a bit on the rich side and idle at higher RPM until they're fully warmed up. The shorter the trips are and the colder the weather, the more noticeable the effect on mpg will be.

[hsong21]

minimo3,

I live in Stamford, CT probably close to you. I am owning 2011 EX35 AWD and i usally get 17mpg with premium gas. Seems too low but I drive mostly local. Only one of weekends go to the City.

[minimo3]

That's about what I'm seeing too so I guess its normal then. I just hope it doesn't drop to 12mpg as the weather turns colder! :-)

[minimo3]

Just filled up my Mazda and the mileage has dropped by about 10-15% too so its definitely the winter blend.

[Hono]

Just filled up my Mazda and the mileage has dropped by about 10-15% too so its definitely the winter blend.

Perhaps the time has come to invest in one of those high mileage battery operated things that provide an additional source of winter warming when the batteries cook off???

Between 16-17mpg (doing the math, not relying on the electronics' best estimate) is what we've been getting since new about 2K miles ago. Not surprising, those numbers are nearly identical to what our G35 obtained. Granted, our driving environment is 90% stoplight-infested urban driving and like most EX drivers I'm not fond of playing pussyfoot with the gas petal...

Although Waikiki temperatures sometime drop down into the high-60's at night, don't think we have a "winter blend" petro here in the islands. However, before we were blessed with that splendid congressional-mandated witches brew that raised food prices worldwide (a.k.a. ethanol), I was averaging 19-20mpg in the G35...