Over the last month or so my 2003 G35 has been giving extremely low MPG. When i purchased it in 2007, i used to get close to 20 mpg (city) and over the last 2-3 years its only reducing. Right now i'm barely getting 12 MPG in the city and about 17 mpg on the highways.

All the maintenance on the car has been done on time at an infiniti service center. Just changed air filters a month ago hoping to get better mpg.

I am aware of the fact that the driving style dictates MPG big time but i drive my G the same way i've driven my mazda and nissan over the years...i.e. gentle. I know that the G is not great on the mpg to start with but 12 mpg is hurting my wallet big time.

Any suggestions/input are welcome.

I've gotten as high as 28 and as low as 17.5MPG over a little over four years

My MPG drops 2-5 MPG in very cold weather

How does your MPG compare with winter and summer?

Do you change your air filter on a regular basis

Telcoman

2006 G35 6 Speed Manual Premium Package A Factory Sirius Radio 110,930 miles, New brakes @ 85k miles, new 2nd replacement set Bridgestone Turanza tires @99930 miles, New plugs @106.7k miles. No mods required, I love her the way she came. Mod money goes to 401K. Regular 87 Octane, all the time.
Last fillup 3/8/10 23.79 MPG @ $2.49 gal with regular 87 octane.

Lately a full tank on the highway gives about 350-360 and in city i get barely 12-13.

In the last 2 1/2 yrs i've changed the air filter twice. Purchased the car with 47K miles, has about 70 K now.

No change in driving style...yes i moved to canada and its peak winter but 12

BTW never ever used less than a 91 octane fuel....usually shell or cheveron but these days at ESSO

Clean your MAF sensor (CRC fluid).

Also, if you're O2 sensors (any of the 4) are starting to go bad, or your cats, then your car will start to run ruch.

it could be a number of factors including:
- colder weather
- type of gas
- gradient degree from being farther north

but it could also be that your car is getting older too....

I was told that aging o2 sensors can cause you to get bad fuel mileage.
Have you changed your plugs??

Going to try to clean my popcharger soon to see if it helps. But probably cold weather and increase in ethanol in the gas around here has hurt too.

I was looking through the owners manual and it says that the spark plugs should be changed at 105 k miles. I'm on 70 K.

I am aware of the fact that changing spark plugs can help but fluids??

Do you guys recommend changing spark plugs and fluids and then chking mpg?

My 96 maxima had a faulty O2 sensor and i replaced it at 172 k miles. If there is a problem with an O2 sensor or any other sensor that is actually causing a rich or lean mixture thereby giving bad mpg...i'd be pretty ticked.

Ever since i purchased the car in june 07, the mpg has been constantly reducing...i agree that the harsh canadian winter can reduce the performance but this just seems drastic.

More than anything, i'm trying to find out if i can do anything to prevent an expensive repair in the future.

1 more thing...last night when i was refilling the windshield washer fluid i noticed that the power steering fluid was on the low end in the container...would like to know what brand of fluids do the forum members use...just for my info

Coolant-
Power Steering fluid -
Brake fluid -

I was planning on visiting the infiniti dealer this evening...do you guys recommend i buy genuine nissan fluids as reflected in the owners manual? Not sure what the dealers would quote on the price.

you mean spark plugs right?

no i have not. was planning to get it done past the 100 k ...thought it'd survive but looks like i might have to change them asap and see if it makes a difference.

By the way I have brand new Toyo winter tires. Tire pressure checked and adjusted twice a month.

is it something a rookie can do? How diff is it?

i got a quote of 800$ + cost of spark plugs + tax

this is for replacing all the fluids and spark plugs.

Apparantly the labor cost of changing spark plugs is 219.99$. I have never changed spark plugs in an Infiniti...have done it on my 96 mazda 626. I am told that it is difficult...but 219$ ...what do you guys think?

I recently moved to canada and live in an apt that does not allow any auto work to be done in the basement. Its freeezing outside..if i need any auto work done i'd have to get it done at an auto shop ...clearly i cannot afford dealership prices

Easy to clean MAF...takes 5-10 min.

Quote, originally posted by crazyboy3012 »

Its lunch time so i called the local infinti... i got a quote of 800$ + cost of spark plugs + tax this is for replacing all the fluids and spark plugs. Apparantly the labor cost of changing spark plugs is 219.99$. I have never changed spark plugs in an Infiniti...have done it on my 96 mazda 626. I am told that it is difficult...but 219$ ...what do you guys think? I recently moved to canada and live in an apt that does not allow any auto work to be done in the basement. Its freeezing outside..if i need any auto work done i'd have to get it done at an auto shop ...clearly i cannot afford dealership prices

Spark plugs will cost your around $7 a piece. I'd recommend replacing with the NGK Iridium IX plugs. You can install them yourself in probably 1.5-2 hours if you've never done it. It takes me around 45 min to replace all 6 now.

Changing out the other fluids is not necessary and really isn't gonna affect your MPG. However, you should consider changing tranny fluid and diff fluid. Coolant can wait til about 100K miles.

I've seen many people have issues with fuel consumption. The few I have seen resolved finally kicked a CEL which pointed to a fuel system leak.

Since you are a 2003, you should call infiniti and give them your VIN # and make sure that the recall was has been done on your vehicle (a long long time ago - fuel filler tube i believe it was)

Edit: Looks like that's only for problems filling the tank.

Dealerships are ridiculous... Changing the spark plugs is no problem at all. If you are good at puzzles, you can change the spark plugs. The hardest part is finding the bolts that hold the coil plug wires in place. It took me about an hour to replace the plugs on my wifes g35x this wekend in 25 degree weather and infinitis aren't even the cars I typically work on.

So you might as well change the plugs being that the amount of miles that it seems like you drive, you're only going to need to replace them once while you own the car, so might as well do it now vs 100k miles.

Another big thing is your tires. Not just your tire pressure but how sticky your tires are along with the tread pattern can severely effect mpg.

Good luck man, if you need help with the spark plug change, let me know, I'll try giving you some pointers.

Thanks pits!!

I have winter tires on....but i'd imagine it should not reduce the mpg by such a huge margin. I guess i'll get NGK Iridium IX plugs as suggested by "tollbooth" and slowly work my way through changing the plugs. I did check out the instructions last night on this website..I think with a little bit of patience I can do it.

Anybody knows if NGK Iridium IX plugs are available at regular auto shops or if I have to order them online?

I used the Iridiums in my Acura because I was able to find them at Autozone. But my wifes G, I couldn't find the Iridiums anywhere and didn't have the patience to order them online and wait. So I just went with the NGK Platinums, the way she drives the car, she wouldn't notice the small differences from one spark plug to the next anyways.

Snow tires easily can effect MPG by 4. Along with the dense cold air of winter, that can effect it about 2-3 mpg more. I'd say running snows in cold weather would easily effect MPGs by 5-6 vs a warm summer day with All Season tires.

Part # is : LFR5AIX-11

I'll buy them online.

By the way how many of us forum members use genuine Nissan fluids for topping up in between service intervals?

I personally can't see "sticky" tires making any difference in sub-freezing temps. The stickiness turns into hardish plastic at those temps.

A short ram warm air intake might actual do some good until the temps go back up to "normal".

You might also take the car to a smog shop or tuning shop and have them run a wide band on your exhaust to see if you're running rich.

F/S:G35/350Z/FX35/Altima Grounding Kits

Quote, originally posted by Mr1der »

go see her, have the most brutal sex ever, then drink most of her milk from the carton and leave.

Faulty O2 sensors(or failing), running rich, or a fuel leak are the likely suspects. I would check A/F ratios first, then look for a fuel leak even though you don't think you have one. Could be on the evap system which is hard to detect.

The point is that snow tires or hockey puck summer tires shouldn't cause a degradation in fuel economy. 60 tread wear drag radials in warm weather, versus 460 tread wear in warm weather might show some difference, but in the cold, I can't see the compound effecting fuel economy.