Hey guys, I have a 2007 G35x that's showing an average of 17.6 MPG on my dash screen. That's considering much of my driving has been stop and go in a city during that time. But This past weekend I did a tad over 400 miles, 90% of which was highway driving. I added up exactly (to the third decimal) how many gallons of gas went for the amount of miles driven and calculated my own gas-mileage (because I was unsure of how accurate the one I was shown on the dash was).

Anyway, I got 16.01 MPG. This is strange to me because first of all, it should be higher than the 17.6 average since the average came from about 50% city driving whereas my recent calculation came from 90% highway driving. Secondly, my gas mileage should be somewhere between 18 and 25 MPG according to Infiniti (although I realize that is often an over-estimate). 16 MPG seems way too low for highway driving, much of which was on cruise control or just generally keeping about the same speed. Only a few accelerations were "spirited" in this 400 mile drive.

Also, I bought this car used over Thanksgiving and it was showing an average of 19.2 MPG. I reset this when I started driving it.

What could be causing such low gas-mileage? Maybe I need to change my oil? (not sure if it was changed at the dealership that sold me the car)...could that do anything? I'm pretty frustrated with this. Thanks!

 

Winterized gas is playing a big part I think.

Check your air filters and if you haven't changed the oil in a while; I'd suggest doing that (make sure you are using the recommended weight oil as well.)

 

i average 13-14MPG with mixed city/highway. the highest i ever got was 17MPG on a full tank reset with cruise control on for like 40 mile trip going 60MPH.

i love my G

 

Not to infer that you don't know how calc correctly....
But did you calc starting with a full tank at zero miles?

 

Here's what I did:

I had 35844 miles on my car when I filled up my tank completely. I drove until36251 miles were on the car. In that time, I had to do a short quick partial fill-up, and then later a full fill up. I added together to the third decimal point exactly how many gallons I filled up that first time to the amount of gallons I filled up at 36251 to a full tank. That was 25.416 gallons. Divided the difference in mileage (407 mi) by 25.416 = 16.014

 

I drive in a mix between city and hwy...averaging 19.9. How fast were you traveling on the interstate? When you start exceeding 75-80 mph the mpg starts dropping pretty quickly.

 

using that method, each tank's calculated mpg might be off a little as your relying on the vapor lock to be consistent. However, over many tanks, you should get a pretty accurate (at least workable) number.

But 16 does seem low for mostly highway driving.

 

I was mostly going between 60 and 80 or so.

What do you guys think I should do?

 

Would it be too obvious to suggest taking it to the dealer to get it checked?

If that's not an option, track the next few tanks and see if their MPG's make sense. If they do, maybe you just got a "bad batch".

 

I guess I'll track it again. But even the avg. 17.6 it's showing is pretty low...although that's for mixed city/hwy. I can't take it to a dealer just like that because I have no Infiniti dealership except like 1.5-2 hours away. I ahve a nissan dealership, but I doubt they would take it in. Also, I feel like the dealer will just blow it off.

 

Have you used the mpg display in the center DOT MATRIX LIQUID CRYSTAL DISPLAY? It can be set to show you an avg mpg readout which is a little easier to accurately read than the one in the Radio/Climate/Nav LCD.
Next time you are on cruise control reset it while driving and it will show you a fairly accurate and current avg mpg reading.

 

Ok im not sure if i get exactly what you are trying to say about filling it up fully, cause the car can only hold 22gal when its near bone dry i believe(mostly 20gal fillup), so how did you come up with 25gal?

If you added gas in separate portions then i suggest you fill the car up fully and drive it till its almost empty to get a better estimate, i hope that makes sense... i get ~21mpg with 80hwy/20city with regular driving(Not pushing it just cruising but spirited at times)

 

That's what I'm using--I don't have Nav.

 

It sounds like you drive similarly to me. I wish I was getting 21...

I bought it 2 months ago and put on about 2000 miles since then. The dealership (a Buick dealer, not Infiniti) asserted that everything was ready to go...but I never got a confirmation of the last oil change. Do you guys think that can make a big difference in mileage? I plan on getting my oil changed, tires rotated, and car inspected some time next weekend hopefully

 

I've had a 2007 G35x for about 3 months now.

My current tank is averaging 13.6 mpg, 100% city driving (avg. speed since my last fill-up 43 miles ago is 13.1 mph). This is heavy stop-go traffic in Chicago and whenever I have a bit of open road, I'm usually romping on it. Typically I'm seeing between 15-18mpg in city driving (with average speed of around 15-20mph).

I drove the car on a 5 hour road trip a few weeks ago and got right around 20mpg on the highway, averaging between 75-80mph.

I'm assuming those numbers will get a little better in the summer. It's a little disappointing, but then again... I didn't buy the car because I thought it would be economical.