egld02155

Has anyone experienced the following? Over the last tank or two of gas, I found that I had to fill it up sooner than in the past. Driving habits and routes unchanged. I routinely drive 100 miles per day, 95 of which is hwy. Pretty abruptly, mileage economy readout all reported a drop from my usual 25-25.5 MPG down to 20, and then all the way down to 10. No change in engine performance. I have never used anything other than regular gas. I use various brands, no favorite. I refilled again last night, and the MPG started at 8, and by the end of the 50 miles of my morning commute, the MPG was back to 24+. I have not seen anything like this in the past. I do reset the mileage calculator when I fill up the tank. I have 50K miles on my car, have done nothing except take care of the interior rattles, the recalls, an airbag sensor, and routine fluids, and am about to put on two new OEM tires on the front. The only thing that has changed is that ithe weather has been nippy...it has been routinely in the 20's-30's in the AM when I leave for work.

T800

Cold weather reduces the efficiency by a small fraction. If you have to do a lot of stop and go, that reduces it too.

But the scenario you have mentioned above is logical. If you reset the mileage calculator when you refil, the computer starts calculating it from scratch. This means for the first 10-20 miles it will try to figure out the mileage. After you have driven for about 10 miles, it starts showing the proper mileage that your car is giving.

Nothing to worry. Everything is normal.

I have experienced that my maxima does not like Shell and BP as much as Marathon or Citgo. It may vary from city to city depending upon what kind of gas the stations supply.

RHMax

I'm still averging 22 MPG, about 370-380 miles per 16-17 gallon fill up on 91 octane. I don't pay much attention the the mileage calculator, just go by miles per fill-up. But the calculator shows 20.x when I check. My car has 22k miles.

Law520

I had several issues with the display of my fuel economy in the past. Through faulty sensors and leak in the gas cap, I've achieved about 50mpg and dipped as low as 8mpg. After getting a set of new tires (on stock wheels) my mpg went from 24 to 21.6. Driving habits unchanged. About 75,000 highway miles.

egld02155

This is a follow up to the responses regarding my 05 Max with transient gas mileage nosedive. I generally do not pay attention to the mileage calculator for the reasons listed in the responses. However, there is no question that the number of miles I got out of a tank of gas went down. I just noted the mileage calculator as an aside, and maybe to correlate with how quickly I returned to the pump. Thanks for responses.

normkit108

Just wondering, have you changed your sensors?

briancopeland

My computer used to say 22 mpg, but it's been steadily nosing down torward 21 mpg a tenth at a time. One, I think it's a running average and I've been doing more city driving lately. Two, I put a Nismo Cold Air Intake on my car a few weeks ago and love to hear it when I get on the accelerator

Seriously, I'd change the oil, reset the ECU, check your tire pressure, and watch where you buy your Premium gas, but wouldn't worry. I'm not aware of any really bad reason you'd be getting worse mileage. If you're really worried about gas mileage you can trade it in for an Altima Hybrid, but I'd rather drive a Quest minivan than one of those, ha ha.

BadBlackMaxSL

iTrader: (1)

Since around December, I have been averaging 17 MPG and in the warm months of the year I average @ 24+ MPG. The AC is running all the time for the heat and defroster, the heated seats and steering wheel, rear defroster and the heated outside mirrors are on a lot too and the hid headlights. I would have to guess that all of this extra power usage accounts for the drop in MPG along with the winter blend of gas. Not to worry, spring is just around the corner; its only 18 degrees F here in Cleveland, OH.

SilverMax_04

Happy to see that there are others here using regular gasoline in their Maximas. Too many take the position of "only the best for my baby." When their driving style may only require regular gasoline (or with frequent WOT calls to the VQ really require premium). I continue to argue that issue on other threads, like this one:

http://forums.maxima.org/showthread.php?t=509540

Now to try an give you some answers to your problems:
- I trust the Max's comupters average mileage calculations more than how many miles you went between fill-ups. I find mine to be quite accruate compared to manual mileage calculations -- because you never fill the tank to the exact same level every time.
- In the old days before computer engine controls and oxygen sensors, cars used to get their best gasoline mileage in the cold of winter. Now, with the new controls, it seems like the winter mileage is generally the worst. The cold snap you mentioned obviously impacetd your mileage.
- If your poor mileage continues, it is likely that you have a problem with your VQ engine or a heavy foot that just recently developed.
- If your poor mileage does not continue, it is likely that the cold weather or a poor batch of gasoline (or both) caused the problem.

Let us know what happens when the weather improves.

Also, new tires have a deeper tread that can negatively impact your fuel economy versus driving on tires with less tread. Be certain to check you tire pressure at least once a month (if not more frequently). I was running 35 psi in my new tires until I noticed the center tread wearing slightly faster than the side tread. I'm now back with the Nissan recommended tire pressures.

Mr. Cummings

I have an 05 sl. My mpg drops dramatically on the hwy when I set the cruise control any higher than 70. Around 70 mph I can get 25-28 mpg. As soon as i hit 80 mph i start getting 20-22 mpg.

egld02155

Very helpful responses. Mileage according to the computer today on the way home from work was 25. Did reset the computer it when I was at highway cruise, and predictably, the MPG jumped up into the 30's. I will calculate my mileage based upon miles driven between tanks, using my pump receipt to determine how much it took to fill it up. As to my choice of regular gas, I actually RTFM'd and it said to use at least 87. The engine has never knocked, and I am very happy with the car's performance. That being said, I occasionally have to stomp on it and it seems to take a second to rear back and respond. Maybe I will try a tank of premium for yuks to see if there is a real difference.

BTW, what is the origin of term, "VQ" -I had to look it up on Google, as I did for "WOT." I know now ;-)

RHMax

VQ is the code for the engines, in our case it's VQ35.

Killah Kane

My car has dropped in gas mileage heavily as well, from about 22mpg down to only about 15mpg. Dont know what to do..

SilverMax_04

Thanks. According to SteVtec (engine expert on this site) it takes between 300 and 500 miles of driving for the VQ's (you know what that means) computer control system to fully recoginze a change of gasoline octane in your tank. So you need to run at least that long before you can be certain that you can get all of permium gasoline's benefits at WOT (you know that term too). Save your money and stick to regular -- unless you plan to race your Max.

normkit108

I changed about every filter you can imagine and I too am avging 15mpg now..

RHMax

How many miles are some of you at when the MPG tanked?

normkit108

I'm lucky to get 300 per tank. I usually tank out at around 270-280 or so.
Just ridiculous.

egld02155

Although this is not an exact science, as I have never run out of gas, I routinely get 400 miles on a tank of gas before I fill it up again. Does anyone believe the 'miles til empty' readout?

M&M

I noticed the gage for the fuel go up and down by a little bit, almost randomly. It would go down below the half mark for example, and then when I look 2-3 min later it's back above the half mark. I'm not sure if that would effect the calculation for the mpg.

!PrjctMax!

iTrader: (38)

You should also check your shoes for excessive lead!

Law520

Yes, my fuel sensor was replaced around 29,000 and now I'm at 75,000. No problems since.

hfj17002

I just bought an '05 SE and the computer says that I'm getting 22.8 mpg. I have 27k miles on my car. I've only filled up a couple of times, but when my car reaches a quarter of a tank, it only takes about 12 gallons to fill up. I thought that was a little odd.

JoAhJoAh

i get the same thing... but some times when it goes back up like maye be 5 mins later it would drop even more than it was be fore it went up.

SilverMax_04

Nissan has it planned that way. You still have 5 to 6 gallons when the light comes on at the 1/8 tank remaining mark. They don't want you to run the tank dry and damage the fuel pump and possibly the injectors.

egld02155

This is an update from my original post. The weather has warmed up a bit here in ATL, and my mileage, based upon some simple arithmetic indicates that my mileage is back to "normal" - a combined intown-hwy 25 mpg with regular gas, with predominantly hwy driving. Never had a bit of deterioration in performance. Go figure. So was the weather the factor, or just a coincidence. I guess I will wait til next year, as Spring is on its way here...

BadBlackMaxSL

iTrader: (1)

The weather here in Cleveland hasn't gotten much better but I have turned off the A/C when running the heat and I have been averaging 20.4 MPG over the last 2 tanks of gas when before I was getting only 17 MPG. My driving habits haven't changed nor has my mix of city versus highway driving, I just turned off the A/C and it accounts for a gain of 3 MPG.

egld02155

Just an update from my previous posts. We did have a cold snap last week here in ATL for a couple of AMs, and once again the mileage calculator dropped from 25 to 18 but it was back around 25 by the end of the day when it warmed up. Not sure what the cause is, but I am fairly comfortable that with two separate instances, cold weather causes changes in my mileage. Signing of til next year...it was 75 today....sunroof: open!

M&M

Yes, I've noticed that temperature makes a huge difference.

Example: couple of weeks ago I took a trip to a friend of mine (1 hour drive all highway), drove there during the day, temp was in the low 40's. Averaged 25.8mpg.

On the way back, same day only couple of hours later, same gas, only at night and temperature in the 20's I averaged 24.4 mpg.

dmpesso

What does replacing your "sensors" do? my gas needled jumps up and down constantly and it annoys me, and BTW ive NEVER and i mean NEVER seen over 20 MPG, im usually getting 16MPG but ive NEVER EVER seen it go over 20 and thats with 90% highway driving too.