New owner-gas mileage

[Bob24]

I knew from reading reviews before I picked up the M45 that it wasn't exactly going to be easy on gas...but holy cow!! I have been taking it fairly easy and using the cruise and I am not even getting 20MPG on the highway.

I filled it up yesterday and today ran some errands and went a couple of places to meet folks for Christmas and I am now at about a half tank. Yikes!

Now that gas is so cheap I don't really care. Although if the car is going to have such poor mileage at least give us a bigger tank so we are not at the gas station every other day.

What, if anything, can be done to improve gas mileage? I know keeping the tires at the proper pressure is big but are there any additives that help?

Another minor dissapointment is the 14 speaker Bose radio system I expect the system would rock but in my opinion it sucks. I like listening to music blaringly loud on occasion and even when I crank the volume as high as she'll go that is only roughly 2/3rds as loud as I would like it to be.

I don't know if Bose/Infiniti are trying to be good corporate citizens and are setting their radios so they don't go beyond the point that hearing loss may occur or what.
Modified by Bob24 at 8:44 PM 12/25/2008

[tytamto]

Regarding your poor mileage, even on the highway, there are a few things to keep in mind: winter gas robs a few MPGs, cold temps will have your engine run on choke for longer (higher RPMs after start up), dirty air filter (unless you replaced it, or had a 30k done recently). Lower tire pressure during cold spells would also make a difference, as would the use of sticky, high rolling resistance winter rubber.

BTW, I just replaced my air filter, and after 30k, the original one was super filthy. Never seen one that clogged up, to be honest. I think that they should be replaced every 15k miles instead. Will report if my mileage had improved at all. I got 21 MPG on the highway (75mhp) and around 17 MPG city (grandma driving) with summer RE050A and the nasty filter.

The other thing about our car, is that the fuel gauge seems to be report exactly what the fuel level is. Some SUV and gas guzzling cars (mainly US made) have gauges that will "lie" to you, moving the needle slower for the first half of the tank, and speeding up during the bottom half. They are not progressive. Ours seems to be dead on and I really appreciate that.

[Bob24]

Thanks,

That is good to know about the gas gauge being right on. I was guessing that my brand new Blizzaks weren't exactly doing my mileage any favors either.

I will be curious to see if the changed air filter makes a difference in your fuel economy.

[zoomie]

I played my system (stock Bose, 14 speakers) the other day, really loud, and it was just that...really loud. My disappointment is that there is very limited availability of Audio DVD so that we could take advantage of the 5.1 surround sound system. I have one Audio DVD and the difference really is incredible.

My M35 has a smaller engine but my highway mileage is 25...on regular gas...I just had my 30K service done and did notice an improvement in the mileage...used to be 21mpg. ]

[tytamto]

Thanks,

That is good to know about the gas gauge being right on. I was guessing that my brand new Blizzaks weren't exactly doing my mileage any favors either.

I will be curious to see if the changed air filter makes a difference in your fuel economy.

Here are a few more things that I think can affect the gas mileage. Some might be minor, but they can add up to as much as 1-2 MPG:

Viscosity and lubricating qualities (freshness) of fluids such as engine oil, diff fluid, and transmission fluid (to lesser extent) affect gas mileage. Even though many experts do not recommend synthetic engine oil to be used in the 4.5L V8; switching to it, along with other fresh fluids would probably help with the mileage.

Adding a trunk lip spoiler is supposed to improve aerodynamic drag coefficient, Cd to 0.27 (per Infiniti brochure). That would help the car slice through the air more efficiently, therefore, theoretically saving a little gas.

Additional weight of items carried in the car, or trunk would also negatively affect mileage and performance.

Running air conditioning increases engine load and will decrease MPGs. Dragging brakes are not helping either.

I am spent... that is all I can think of.

[AD1787]

I am getting 18.3mpg in 90% in-town driving on my M45 w/ Mid 50 degree weather, just after my 30K service. I am happy enough with that.

Oddly I only get 0MPG when it sits in the garage. LOL

[Q45tech]

Most people don't research EPA ratings and don't find out the maximum speed is 61 mph to achieve published Highway MPG numbers.http://www.fueleconomy.gov/feg...shtml

[tytamto]

Most people don't research EPA ratings and don't find out the maximum speed is 61 mph to achieve published Highway MPG numbers.http://www.fueleconomy.gov/feg...shtml

Contradictive info on their website. Link: http://www.fueleconomy.gov/feg/factors.shtml

"Driving at higher speeds increases aerodynamic drag (wind resistance), reducing fuel economy. The new EPA tests account for aerodynamic drag up to highway speeds of 80 mph, but some drivers exceed this speed."

[daveM45]

That's expected. I also live in snowy MN. With the winter tires and longer warm ups I give it my M45 get 13/20 now. In summer 15/22.

If you actually do the speed limit you can get 26 on the highway but things drop in a hurry once you go over 3K rpm. Unfortunately that's usually where I drive....

Part of the mileage has to be the height of the car. Its not the low streamlined wedge of some of the others. I'm willing to give up a couple mpg for the headroom and easier entry. The other part I blame on the engine design/gear ratios. Hopefully that improves in future models. The 2008 finally has variable valve timing but I haven't seen if that helps flatten out the horsepower curve. The 2008 still shows the 5 speed for the M45. They'll need a gear ratio change or 6/7 speed to take advantage of any improvements.

[Bob24]

Great info guys. I found it interesting that they don't recommend full synthetic for the V8. Thankfully I don't drive as much as I used to and with the gas prices where they are at it won't be too big of a hit.

[Q45tech]

The test proceedure adjustment in 2008 reduced the city/highway MPG by 2 vs the 2007 proceedure.............the post concerned a 2007 model not a 2008.

Important to read the background info of a poster.

Also that 80 mph peak was for a single slow pass not a steady 80 mph cruise.

"It will include a top speed of 80 mph (129 km/h) and an average speed of 48 mph (77 km/h).

[AlbuquerqueM45sport]

I just got back from a trip from Albuquerque to San Diego and back. I set the cruse control at 90MPH and just about never did less than that, sometimes much more. I got a little over 19MPG. I really am not that concerned about MPG in a high performace luxury sedan like this, but there are my numbers. By the way, I run Micheline Sport / AS with 35PSI all around, I have a full size spare and run the auto feature for the climate control. I had 3 adults with a full trunk going and 1 adult, with very little in the trunk coming back with no difference in MPG.

[zozoka1212]

There is another big factor. The tires. There is a roll resistance number for each tires. It could be 2-3 mpg differences between tires.

http://www.consumerreports.org...v.htm

Also the fuel octane have good play in gasmilage. Among with all others you guys said.

zozo

[Q45tech]

Fuel BTU per gallon not octane is important for cruising since the load factor is so low, detonation doesn't occur without attempted acceleration.

The lower BTU of E10 results in a >3% decrease in MPG even though E10 might have a higher published octane rating.