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Infiniti M35/M45 Real World MPG



  • shmangshmang Posts: 297
    Maybe all the M45 (and M35) owners are used to the terrible gas mileage and trying to forget about the pain? For now, the gas price is low, so no big deal, but it must be hurting back in late 2007 and majority of 2008. :mad:

    I am used to the bad mileage already, but just feel it odd that I get almost the same gas mileage on city and highway - well a little over 1.5 MPG difference. This is not normal to me, thus the post/question.

    Anyone mind share their experiences/thoughts? ;)
  • avj23avj23 Posts: 4
    I have a new 2008 M35x with 500 miles on it that is getting about 10 MPG (mostly city) and revving high 2900 RPM's at 70 mph. It does not seem to go into overdrive. Has anyone else had this issue or do you think it will improve after some additional miles?
  • shmangshmang Posts: 297
    If it is at 2900rpm at 70mph, it is in overdrive. The M is geared for performance and you are already in the overdrive gear. Mine is the same (as well as other ones I test drove). On my Honda, it revs at 3550rpm in 5th gear at 70mph (again, sporty car and geared for performance).

    Even for break in period, with AWD, 10MPG seems low. Unless it is very congested city and you have a lead foot and somewhat short trip (less than 10 miles each way). I get 15 when driving very aggressive in heavy city traffic and get 18 when take it easy.
  • avj23avj23 Posts: 4
    Been driving easy during the break-in period so it could get worse if I drive agressively. If the car truely revs at 2900 RPM's at 70 MPH, I think that would explain the gas mileage. In the last two days I've been in a Scion and Chevy Cobalt that were revving at under 2500 RPM's at 70 MPH.
  • My 2009 Cadillac CTS revs between 2100 & 2200 at 70. I guess that explains the Infiniti reputation for bad fuel mileage.
  • shmangshmang Posts: 297
    Well, the high revs does not necessarily explain the bad gas mileage. Just as I said, my Honda revs higher and get 32 MPG on the highway (at 70MPH), which is a number the CTS can not reach. Not sure about the Scion or Cobalt though. But they are much lighter and has much less hp to begin with.

    Infiniti could build a more efficient engine, but I think fuel economy is simply not their focus point.
  • avj23avj23 Posts: 4
    Is yours AWD? What kind of MPG are you getting and what kind of driving.
  • Automatic, RWD. 95% highway (usually about 75mph), 27 mpg.
  • james27james27 Posts: 433
    I have a 2006 M35x. Mostly highway, it's about 20-miles to work, and I typically get around 20mpg, the best I've done is about 26. If I spend a lot of time in the city (not very often), it does drop to the mid-teens. I do drive fast, but don't put my foot into it that often. Definately not in the slow lane.
  • shmangshmang Posts: 297
    Well, that sounds about right, except the 26MPG. I have never been able to get anywhere close to that - even when fuel economy is top priority. The best I got so far is 23.2 on highway 65mph, 70F, no A/C.

    What did you do to get to around 26? I need to know in case the gas price goes to $4/gallon again :cry:
  • james27james27 Posts: 433
    200 miles on cruise control with gas that didn't have any ethanol in it, cool, but not super cold, level roads, no traffic. Per volume, alcohol doesn't have as much energy as gasoline and lowers your mileage. Hard to find depending on the locale and the season, but does make a difference. It helps if you run the tires at the high end of the recommended range as well.
  • 2900 RPM at 70mph is normal for an M35. It is designed to rev high for sportiness. Check you trip computer for you av. speed. I get 19.5 MPG for an av. speed of 30mph. Keep you tires at 34-35 PSI. Use premium gas from a quality brand. Keep the windows up will driving above 40mph. If nothing works you have a problem. 10 MPG is too low even for a new car.
  • Note the 2009 M35 RWD with the new 7 speed trans has higher top gear. I'm seeing exactly 2000 rpm @ 60mph which would put it at about 2350 @ 70mph (I'll check it @ 70 next time I'm out). My first half tank was 23 mpg (computer) with probably 70% highway, 25% suburban & 5% stop and go (easy driving during break-in).
  • avj23avj23 Posts: 4
    Have just over 800 miles on the car now and still averaging at best 12 mpg almost all city/short trips. Took it in to the dealer and they said its fine, "it should improve slightly after break-in period." Wish I would've checked this site first might not have bought it. Nice car though.
  • james27james27 Posts: 433
    Short trips, cold starts, stop and go will always be a problem with a high-performance car, especially one weighing about two-tons. You might want to use the trip computer and see what your average mph and distance traveled guess is the car might not be fully warmed up and you spend more time idling than you think. A diesel works much better, since it is very efficient at idle.
  • I have an used infiniti m35 sport 2006. It currently have 67k miles and I have been suffering terrible mpg driving here in nyc. My city driving at best is around 10.5 mpg. My combine city/highway is around 16mpg. Anyone know what is wrong with my car? Is this normal for nyc driving? It is not even heavy traffic where I live. I bought this car to the dealer and they told me this is normal.
  • shmangshmang Posts: 297
    What is your daily commute distance (each trip)? When you say city, was that like a stop light every quarter mile to half mile? What is the % for your combined drive, like 40% highway, 60% city?

    Keep in mind, the M is very thirsty to begin with.
  • I commute about 5 miles round trip. City driving as like stop light every block or every two blocks. It's not like one block the light will be green and the next block is red. It is consistent most of the time so I don't have to stop until like 5 blocks. My combine driving is about 30% highway and 70% city. Is this normal to get 10mpg? sometimes even 9mpg? I thought my fuel injector was dirty or something since it was a used car but I add some additive and it still didn't help much.
  • james27james27 Posts: 433
    In 2.5 miles (your one-way trip distance?), the car is not warmed up. Yes, the temp gauge will say it is, but it takes longer than that to fully warm up everything. In that time, the car will be using more gas. You're just getting to the point where it can start to hit its peak when you shut it off.

    I have a 2006 M35x and my average tank mileage is about 20-21mpg, but I travel 19-miles, mostly highway each way to work. My mileage went up a little (maybe around 1mpg) when I switched to synthetic oil. I've had the oil tested periodically, and can safely run about 10k miles between oil and filter changes. You probably wouldn't want to do that with all of those short trips.

    In NYC you might get run over by the cabbies if you don't accellerate fairly quickly, but it can make a huge difference if you take it a little easier, and don't brake late when you see the light is red ahead of you.

    I'm seriously considering a new Mercedes E-class diesel. It should be great in short trips and on the highway (rated at 32mpg highway).
  • Well I don't live in NYC where there is a lot of cabs. I live in brooklyn which is more regular streets. I don't really think it has to do with the car warming up because from time to time, I let the car warm up for 5 minutes before I drive and it is the same thing. I drove 10 miles before I reset my computer and I am still driving at around 10 mpg city. I was thinking about getting a fuel injection cleaning and switching to mobil 1 to see if it helps. My friends m35x is getting about 13-14 mpg city driving compare to mine 9-10mpg.
  • shmangshmang Posts: 297
    I believe your short trip is the key - if you let the car warm up (by not driving it), it just make your MPG looks worse, since it is calculated based on miles driven divided by gas used. When idling for warm up, you get zero MPG. I would let the engine warm up for 20-30 sec. at most and then drive moderately for a mile or so before go pass 3.5K rpm.

    So, with your short trip and a lot of stop light, 10-13 MPG is not a surprise. I have a M45 and if I reset the trip computer at start up and drive the first 2 miles (45 MPH zone with basically no light), my MPG reading would be somewhere around 13, but since my commute is 22 miles one way, I normally get 17-18 without A/C and 15-17 with A/C.

    So, short trip makes the car running at inefficient zone all the time - so it is not a surprise for your MPG. If you are driving a small I-4, this is not that noticeable, but for a big 6 (or 8), it is a very significant factor. Next time, reset your MPG calculation before hit a highway and run at least 15 miles and see what MPG you get. I will be surprised if it is not over 20.
  • So should I even bother doing a fuel injection cleaning and switch to mobil 1 or live with the fact that my car will always average around 10mpg.
  • shmangshmang Posts: 297
    If for fuel economy purpose, I would not do either. But for better care of the car, mobile 1 sounds like a good choice, but you still need to change the oil every 7500 miles or 6 month which ever comes first - consider your short trip and stop & go traffic, which is very hard on the engine.

    What;s more important is: make sure you run the car for at least 15 miles one way once a month (or more often) with a few good accelerations. This will clear up all the carbon build up in the engine caused by all those short trips.
  • Isn't it when you get mobil 1 you don't have to change the oil as frequently? Thats what the mobil 1 extended performance claims to do?
  • nolicnolic Posts: 11
    Inflated tire pressure to 34 PSI on my 2008 M35 increased my average MPG (combine) to about 18 - 19 and I also used Mobil 1 synthetic oil (5W30).
  • shmangshmang Posts: 297
    Isn't it when you get mobil 1 you don't have to change the oil as frequently? Thats what the mobil 1 extended performance claims to do?

    That is correct. But, with your driving style, I would change oil more frequently, since short trips are hard on the engine. So, with regular oil, I would do it every 3000 miles and with Mobile 1, you can extend it to about 7500 miles, but, still, I would NOT go way pass 6 month (7-8 month might be OK) though.

    Yes, inflate the tire to 34 PSI will provide improved MPG - with some sacrifice of riding quality, not by much though.
  • I have owned an '06 M35 RWD since April '05 which currently has 82,500 miles on it. I live in South FL, commute 60 miles each way averaging 21.8 mpg running between 75-80 mph. My only complaint is the high RPM (3,000 @ 80 MPH). Presume that the newer models with 7 sp tranny will help...
  • m4mm4m Posts: 76
    Atlanta, GA to Orlando, FL: Trip Computer: 497 miles, Elapsed time: 7hr 19 min. for an average speed of: 75.3 MPH. Some luggage and about 1/2 way there and back A/C was on. LOTS of cops but they were all busy writing tickets. Still saw 90+ a couple times.
    Speed limits vary from 55 to 70 with probably 70% of the trip at 70mph.

    So, overall MPG for this trip, with an average speed of about 75MPH, turned out to be 23.8 MPG on premium. And I blew the doors off an Audi A6 and a GS350. Probably dropped my average by 1!
  • mltsurgermltsurger Posts: 102
    I have a M45X with 20,300 miles at this time.I love driving it and try to drive responsibly,but the sound when punching it is great.I average 21 miles to the gallon.It recently has been very cold and am getting around 20.I always use B.P. white Premium.
  • mltsurgermltsurger Posts: 102
    Sounds like a fun trip.How many gas stops? Has anyone ever gone over 140 mph with the infin.It is supposed to go 155.You really wonder about the handling at 140.If my driveway was longer I would like to try.
This discussion has been closed.