Fuel Economy? (2007 Infiniti M35)

[jagplates]

After 1000 miles of local driving (suburban, not city), my trip computer says my 2007 M35 is averaging 14.8 mpg. The window sticker claims 18 mpg city. I know that the manufacturers lie through their teeth about mileage ratings, but 14.8 seems pretty bad for a 6 cylinder car.

What is normal for the M35?

Postscript. The 14.8 average was entirely with my wife driving. Today, I took it out for 100 miles of 70/30 freeway/local driving, and averaged about 21. I hope it is true that the mileage will improve 1 or 2 mpg when the car is fully broken in.

Update:. I finally got the chance to get out on the open road for a few hundred miles. 300 miles of mostly freeway driving, and the computer is saying 22.3 MPG. This was mostly with the cruise control set to about 72 MPH. After a while, I tried an experiment. I put the car in manual 5th gear, so it wouldn't downshift at the slightest bit of acceleration. I don't know whether that helps economy or not, but it seems like it should.

Modified by jagplates at 9:23 PM 10/24/2007
Modified by jagplates at 9:50 PM 11/4/2007

[szh]

1. That mileage is actually not bad for all low-speed driving, with lights and all. If you did about 50-50 highway and city driving, you should average near 19 to 20 mpg over time.

2. It will get a bit better after the first 5k to 10k miles - perhaps as much as 1 to 2mpg better.

But, it is not going to be dramatically different for most other higher-powered 6-cylinder cars really!

Z

[exbmwdude]

A lot of it has to do with the gearing designed to produce good magazine numbers. Do we need a 3.55 rear axle in a sedan (with no 6-th gear)?Should we be running the engine over 3krpm at 80mph on the highway when even 4 cylinder cars are running along happily at 2500 ?

Don't get me wrong - I love the car but the 90/10 rule applies here. When I'm out to have fun (10%) and drive the car hard, the gearing is perfect. but most of the time when I'm in family mode (90%), the car needs taller gearing or a 6-speed, or both. Most other sport sedans have a 6-speed so you can have your cake and eat it too. Why Nissan couldn't just buy a GM or Aisin 6-s-speed unit I have no idea. You don't *need* to make your own trannies any more in the car biz.

exbmwdude2006 M35S

[Q45tech]

Manufacturers cannot lie much because the car is put on a special in lab dyno and follows a preprogrammed EPA created software driving routine...........sure they can fudge a rounding error up to next mpg but beyond that they'll get caught. EPA randomly samples and tests models and brands and fines those that cheat. It is extremely rare for a manufacturer to fail this comparison double check they usually actually do better than the label by 0.5 mpg so they don't risk a multi million fine $10,000 per unit sold.

If you exceed 60 mph, carry passengers, or use AC, or drive trips shorter than 30 miles per crank in cold or hot weather, you are not following the measurement test proceedure and of course mpg will be worse.

Also you must use the same test gasoline as EPA called indolene clear which is rigoursly quality tested and is nothing like the gasoline supplied at the pumps especially the mileage robbing ethanol E10.

[Q45tech]

For 6 years the equal weight 90-96 Q with a 3.538 rear diff gear barely got by with a 0.694 top gear which yielded 2666 rpms at 80 mph...........in low load cruising with AC on and a passenger and trunk load the engine lugged badlyly at 50 mph [1666 rpm] so 5th gear was set at 0.83 instead of 0.694..............this 20% higher gear ratio means 20% higher rpm and at least 10% less mpg at the same speed.

Members can alway downgrade the rear diff ratio to 3.31 or 2.83 or 2.91 to improve mpg at the expense of acceleration.

Hard to have cake and eat it too with a 5AT..................but heck of a lot better than the 4AT in use until 2001.

[sub9lulu]

lol i got 17-20 mpg out of my 4.5L v8 m45

[TexasMadrone]

Having just returned from a 2,640 mile trip with my '03 M45, I'm pleased to report that at 70-73 MPH cruise controlled speed, I got as high as 26.8MPG. At 63-65MPH cruise setting it dropped to 25-25.5MPG range. The terain varied from gulf coast flat, to hilly Alabama, Tenn. and Virginia valleys. This seems to indicate to me that the M is designed at best efficiency(2100-2300rpm) at around the 70MPH mark. Any thoughts? My typical town mileage is from 16.1-16.8MPG. I'm not known for a "soft pedal" but on the other hand I don't burn out at every opportunity either.FYI: Odometer at approx. 31,000 range so it's not a high mileage M.

Texasmadrone

[sub9lulu]

damn, 26mpg is almost unheard ofbut then my minimum speed is like 85mph ....

[M45-Zero260]

I feel fuel economy is a mixed stew of many ingredients. For one, I reset the odometer at every fill up. My wife and I switch off every other week with the car. I have noticed that city driving, I am somewhere between 17-19 mpg, and when I fill up and hand off the car to her, it is usually somewhere between 14-16 mpg when she hands it off to me. Perhaps she is a different breed of heavy-footed drivers, has more of a "grip it - and - rip it" soul, or she enjoys the pure pleasure of having the unique styled (always clean) black car at the intersection with the chrome rims, just waiting for the red light to change green so she can muster up all 340 horses with the VDC off. Who knows, either way, situations change, time of day, traffic lights, accidents, warm-up, highway driving, sitting and talking with her sister for almost an hour with the car running, etc. My point is this: Although gas prices may suck as opposed to years ago, after I get done pumping in $56.92 of Premium into this beast, I smile, because as I look around at the other Taurus's, Minivans, and hatchbacks, I remember why I bought this car in the first place.

[TexasMadrone]

M45-Zero260Great post! Your closing comments hit it on the head!! Just love to merge on to the Houston Freeways at warp speed with the 340hp/333ft.# under the pedal. Eyes pop when they see it. Especially the Lexus boys.

TexasMadrone

[MattB]

Is the Y50 a lot heavier than the A33? My I30 seems to consistantly get around 25mpg in mixed driving. I can't imagine the additional half-liter of displacement making a huge difference in fuel economy unless the car is a lot heavier...

[Q45tech]

RWD has ~~ 3-3.5% more frictional losses than FWD.

[szh]

RWD has ~~ 3-3.5% more frictional losses than FWD.

Dennis,

I assume this is because of the additional drive-train components right? The external factors (tires, wind resistance, etc.) ought to be the same for both, correct?

Z

[exbmwdude]

RWD has ~~ 3-3.5% more frictional losses than FWD.

That's only true of transverse FWD versus RWD. Some FWD uses a north-south engine arrangement and therefore suffers the same loss. Like my old Chrysler 300M for example.

exbmwdude 2006 M35S

[MagicM]

My 2007 infinti M35X mpg is almost the same as my range rover in city, so don't feel to bad

[rubicon-7]

wow...was thinking about selling my G35 for an M45, but I put on 25k miles a year......don't know if I can give up 28mpg....Guess I thought the M was do a little better....trade offs with hp definately...

[MagicM]

Problem is the gearing, and only having 5 speed auto on it. On mine no matter what gear you're in the rpm seems too high, and the transmission seems to hold the gears alot making it rev at 3-4k rpm. not to mention having a curb of close to 2 tons with awd doesn't help eithier. If you want supreme highway MPG with horsepower consider a z06 corvette or normal c6, they're rated at 18 mpg / 28 mpg. 500 + horsepower with economy car mpg pretty good . My friend has one and if you granny foot it, the MPG is simply amazing for such a massive engine, i can actually vouch for it's rating. Until you step on it and, then it goes into single digits .

[StarPD]

After 1000 miles of local driving (suburban, not city), my trip computer says my 2007 M35 is averaging 14.8 mpg. The window sticker claims 18 mpg city. I know that the manufacturers lie through their teeth about mileage ratings, but 14.8 seems pretty bad for a 6 cylinder car.

What is normal for the M35?

Postscript. The 14.8 average was entirely with my wife driving. Today, I took it out for 100 miles of 70/30 freeway/local driving, and averaged about 21. I hope it is true that the mileage will improve 1 or 2 mpg when the car is fully broken in.

Modified by jagplates at 9:23 PM 10/24/2007

You already answered your own question with the difference in fuel mileage between you and your wife driving. Your problem is not the car, it's your wife. No offense intended but women drive differently than most men. Watch them as you approach a red light or stop sign. For some reason, women seem to actually accelerate when they see a stop sign or red light, then slam on the brakes at the last second. Then when the light turns green, they floor it and exceed the cruising speed they want at first, then gradually slow down to whatever speed they want to go. They also can't seem to hold a steady speed in traffic. They are constantly accelerating and decellerating.

My wife is a classic example, as much as I love her. She drives a crappy 2000 Ford Focus wagon, and her fuel mileage mixed city/freeway is usually around 26 mpg. I drive the same car in the same conditions and get 32 to 34 mpg. The tipoff is her brakes. She needs new brakes about every 20K miles. If I say anything about backing off the gas when approaching a red light, she gets huffy and insists she already has, but I can hear the engine still accelerating. Can't win that argument, so I gave up.

Keep an eye on your brakes. If your wife drives it mostly, expect short brake life, and don't expect her to notice the brake wear indicator noise. She won't until the backing plates are eating the rotors. There's more, but I won't belabor the point.

I don't let my wife drive my '05 Q45. Guess why.