City & Highway mileage

[M45Runner]

Ok, we all know that M35/M45 is not build for gas mileage. But, what I noticed is: When I driving in city (light traffic, with stop lights), I get around 19-20MPG, but on highway, I barely get 21-22MPG. Is this normal for M45? This is assume I drive it easy - When I do drive it hard, I only get around 15MPG, which we all know why

[EniGmA1987]

dont know what is normal for the 45, I have a 35. If I try and get good milage I can do about 27-28mpg highway, 19-20 city. If I dont try, I can get 12 city, 15 highway...

Except for lately. This last tank I have been getting aweful mpg, which is kinda weird since the gas is lasting me a tiny bit longer in total miles. I dont really get it, maybe there is something wrong with my car. Normally I get around 250 miles per tank, this one I have almost 200 and still have a couple lines under half a tank, yet my mpg average is quite a bit lower than when I am normally trying to save gas. And I noticed that when I lightly accelerate with this tank, I get worse than I used to when I lightly accelerate. But whatever, I *normally* get 27-28mpg highway, 19-20 city when I try to save. So your getting a couple more than city seems kinda weird to me.

[M45Runner]

Wow, that is a big difference. What year is your M35 - is it with the 7spd or 5spd?

IIRC, the M35 also has a 20 Gal. tank, so if you only get 250 miles per tank - assume 15 Gal. consumed at the time of fill up, that only gives you about 17MPG. And if you get 27MPG on highway, that means you can drive for almost 500 miles without fill up Maybe I should get M35 instead.

[ken in az]

dont know what is normal for the 45, I have a 35. If I try and get good milage I can do about 27-28mpg highway, 19-20 city. If I dont try, I can get 12 city, 15 highway...

Except for lately. This last tank I have been getting aweful mpg, which is kinda weird since the gas is lasting me a tiny bit longer in total miles. I dont really get it, maybe there is something wrong with my car. Normally I get around 250 miles per tank, this one I have almost 200 and still have a couple lines under half a tank, yet my mpg average is quite a bit lower than when I am normally trying to save gas. And I noticed that when I lightly accelerate with this tank, I get worse than I used to when I lightly accelerate. But whatever, I *normally* get 27-28mpg highway, 19-20 city when I try to save. So your getting a couple more than city seems kinda weird to me.

Always do a hand calculated mpg test as the mpg indicator on your dash could be off from time to time. Mine is normally spot on but there have been a few occasions that it has read lower than actual by more than 1mpg.

Also fuel gauges don't seem to be the most reliable on these cars. I know when I fill up, sometimes the gauge goes all the way above the full mark and other times it stays just below the full mark, even though I top off with fuel into the filler neck

And M45Runner: I notice that same Phenomenon in my 06' M45 when I don't care about gas mileage, but if I really pay attention to the Instant MPG gauge in the screen I can increase my fuel economy very easily. These M's are very thirsty - tip in the throttle and they will drink it up fast if you aren't light on the throttle.

I can say that since we got our "summer" fuel I've noticed my fuel economy has dropped about 1mpg and couple that with using the AC - another mpg hit. Without AC with winter fuel and I can get upwards of 26-28mph hwy when I drive like i'm drivin miss daisy.

[EniGmA1987]

My M35 is a 2006, 5 speed automatic. And it has a 15 gallon tank. Highway milage doesnt play a big role for me since I only drive about 5 or 6 miles on the freeway each day. Pretty much all my milage calculations are based off of my city numbers. But I have reset the counter a few times when I get on the freeway, and driving from the onramp all the way to my drivway I consistantly average 27mpg.

As Ken said, keep that screen on and you are much more conscious. I can drastically improve my milage by driving with the fuel economy screen on at all times.

Also, dont use cruise control, I get another 1 or 2 mpg just driving myself. and keep VDC on, I get 3 mpg less when VDC is turned off.

50 miles per hour is the sweet spot on my M35. I can get 31mpg if I constantly cruise at 50mph, with cruise off and VDC on. That is with light air conditioning too.

Quote »And if you get 27MPG on highway, that means you can drive for almost 500 miles without fill up[/quote]I get a slight bit more per tank if I really try. I can drive from Corona, California to Las Vegas, drive around a little bit to some casinos, and drive halfway back before I have to fill up. And even then I dont *have* to fill up, I just like to fill up when I am down to a couple lines left on the gas gauge.
Modified by EniGmA1987 at 7:21 PM 5/21/2009

[M45Runner]

Without AC with winter fuel and I can get upwards of 26-28mph hwy when I drive like i'm drivin miss daisy.

Wow, 26-28MPG on a M45? At 60MPH maybe, even that I doubt I can touch that number. OK, I have to try with the instant MPG screen on all the time. What else? Tire pressure, no radio, no light, no A/C?

[M45Runner]

50 miles per hour is the sweet spot on my M35. I can get 31mpg if I constantly cruise at 50mph, with cruise off and VDC on. That is with light air conditioning too.

I don't mind drive a bit slow when trying to save gas, but where can you drive 50mph CONSISTENTLY - far right lane on a highway?

I would be happy if I can get to 25mpg on the highway follow traffic.

[ken in az]

What is weird - I notice the same mileage between 68 and 72mph as I do trying to be nice at 55-60mph. I'd even lean towards getting better mileage at the higher speeds but I have never "tested" that theory so I don't want to make false claims.

I've never noticed a difference with the VDC off but I can tell you that when "she" drives the car the fuel economy plumits. When I got back from my trip last week I got in and saw it at 17.2mpg I honestly was shocked. I've never gotten that low of mileage. After 100miles of me being nice to it I got it back up to 19.5mpg's.

What really ticks me off though is that in my 7000lb Dodge Diesel making 480rwhp and over 1100rwtq I could still manage 20mpg and run 14.5's at 100mph at the track! This might help explain why I want to mod the hell out of this thing - lol

[EniGmA1987]

I don't mind drive a bit slow when trying to save gas, but where can you drive 50mph CONSISTENTLY - far right lane on a highway?

I would be happy if I can get to 25mpg on the highway follow traffic.

city streets near me you can easily go 50 for a while, or at slower times on the freeway. I live in Sothern California, so 85 on the freeway is normal fo no traffic. Traffic gets between 50 and 60mph, so when there is traffic I cna just cruise along at 50 and make the other people go around me. they usually end up putting their brakes on hard not long after anyway and they are right in front of me instead of right behind me. Would be much better if they simply went a stable speed instead of hard accel, then hard brake followed by hard accel.

What is weird - I notice the same mileage between 68 and 72mph as I do trying to be nice at 55-60mph. I'd even lean towards getting better mileage at the higher speeds but I have never "tested" that theory so I don't want to make false claims.

No, thats quite true. I see that as well. While is is quite good milage for me up around 70, I still get another 1mpg or so driving 50 rather than 70. I do not however see the same thing at 90 on the freeway. at 90mph I generally get around 20-22 mpg
Modified by EniGmA1987 at 4:09 PM 5/21/2009

[tigerclaws1318]

It's ok, I only average 12mpg all the time no matter how slow I drive. Mix driving is around 14mpg.

[M45Runner]

How come you only get around 12mpg. You serious need a tune up, unless you brake every 20 sec. and drive short trips ALL the time AND drives very aggressive.

[maqueswell]

My M35 is a 2006, 5 speed automatic. And it has a 15 gallon tank. .

The M35/45 has a 20 gallon gas tank.I average 18.5 in the city and 27-8 on the highway, and i'm easy on the pedal until i have to access the highway or pass some slow (below posted speed limit) moron.

[BigP]

So far I'm getting 17 city and 21-22 highway. About what the sticker says. (06 M45). I drive it fairly hard though.

By the way I have a habit of only getting 10 gallons of gas at a time. I usually let it run down to within 5 miles of empty and I reset the trip odometer and check my mileage that way. 170 miles = 17 MPG. No math really needed.

So far the screen readings have been close to actual. Haven't run out of gas yet!

[tigerclaws1318]

How come you only get around 12mpg. You serious need a tune up, unless you brake every 20 sec. and drive short trips ALL the time AND drives very aggressive.

The car only has 30k miles on it and I drive it easy 85% of the time. My trips are normally short and sometimes mix highway/city. I try to get over 14mpg but no matter what I do it doesnt work. lol

[jbillion]

I average around 13, mostly city driving. Even on long highway trips, with cruise control around 65mph I only get 17.

[kingpin]

best was 21.5 mpg worst was 7.2 mpg yes 7.2- in winnipeg - 66 with the wind chill - i was their on business first and last f n time !!!

i use 94 octane all the time - i average 17 to 18 mpg with higher octane

[EniGmA1987]

I said my average numbers before, but since people are bringing up their worst... The first week I bought the car I averaged 5.8 miles per gallon on my M35. I was driving HARD.

BTW, anyone besides me notice that the Ms rarely say an odd number for the decimal place in the milage?

[M45Runner]

Wow, I guess the Y34 ('03 & '04) model get worse gas mileage. Maybe it is partly due to the age and mileage - we have similar engine and transmission right? Heck, Q45 get better mileage even though it is heavier.

[antzrus]

I use 89 Octane. I usually get 12-15 in town. On a flat hi way @ about 60 mph I get about 24 mpg. In regular hi way driving I get about 22.5 mpg.

The high RPMs, these machines where partly built for acceleration/thrill, not thrift...

But then most of us bought her for that reason.

[Double E]

That's funny...I was noticinfg that I always see an odd number behind the decimal place.

In mixed driving, but mostly highway, I've been averaging 22.3 for 2 months.

Even if I romp on it for day, I guess the average still works out that I'm not killing my results.

[szh]

On my 2003 M45 (Y34), I regularly get between 15 to 16 mpg with a mix of highway-city driving. Sometimes closer to 17.5 to 18 mpg if I use the highway more than 75% of the time - but it is stop and go in heavy traffic, so not always steady driving.

FWIW, once I get off the highway, at the end of the ramp and around town, I drop the car in 4th gear max setting, so that it does not lug in and out of 5th at lower speeds. This does not seem to affect my mileage too much.

Also, I have done posts with mileage (as read by the car systems) readings ar various steady highway speeds ... those are interesting to note. You can get 25 to 26 mpg with steady 65 mph speeds (cruise control on, level ground) pretty easily.

Z

[jbillion]

What do you mean by 4th gear max? Is that usinfg manual mode?

[EniGmA1987]

Even if I romp on it for day, I guess the average still works out that I'm not killing my results.

It depends on how long it has been since you reset the counter. I usually reset it every other fill up, just so I can see what I am actually averaging all the time, not the average since I bought the car.

[ken in az]

Wow, I guess the Y34 ('03 & '04) model get worse gas mileage. Maybe it is partly due to the age and mileage - we have similar engine and transmission right? Heck, Q45 get better mileage even though it is heavier.

Really the only difference between the two cars is gearing and the fact that the prev model year is rated with a higher power rating (I Know SAE correction factor changed - I still think you guys have more power)

Your Diff ratio is 3.13:1 and ours is 3.36:1

Your TC Stall ratio is 2:1 where ours is 1.85:1

Your Gears in the trans are tallerYours = 3.54 1st gear, 2.26:1 2nd, 1.47:1 3rd, 1:1 4th, and the same .83:1 OD 5th gearOurs = 3.83 1st gear, 2.37:1 2nd, 1.52:1 3rd, 1:1 4th, and the same .83:1 OD 5th gear

Tire size is slightly smaller in diameter but nearly a half inch but I doubt that had anything to do with fuel economy.

I figure that the lower gearing is causing your engine to expell more effort to do the same work as the newer car. I know it sounds backwards but the lower gearing may only be helping at highway speeds, and that is where aerodynamics come into play.

Your "reported" Coefficient of Drag (CD) = .31Our "reported" CD = .29

So being slightly dirty when it comes to drag may be against you at those higher speeds.

You guys have it easy since a 3.69 300zx TT rear diff with VLSD will bolt right in you can offset the rear drive ratio to yeild better acceleration and potentially better fuel economy.

[M45Runner]

It depends on how long it has been since you reset the counter. I usually reset it every other fill up, just so I can see what I am actually averaging all the time, not the average since I bought the car.

Yeah, I do the same most of the time, so it is very sensitive right after reset and will not change at the end of each tank - even I drive super sensitively.

[mjlyn]

Also, dont use cruise control, I get another 1 or 2 mpg just driving myself. and keep VDC on, I get 3 mpg less when VDC is turned off.

Modified by EniGmA1987 at 7:21 PM 5/21/2009

Why would VDC have any effect on MPG under normal driving conditions?

[szh]

What do you mean by 4th gear max? Is that usinfg manual mode?

Yes.

On the 2003 (and maybe the 2004 too - I don't know), when you first shift into "Manual" mode, the upper limit is simply set to 4th gear - the car shifts up and down normally - and the shift points (speed and revs) are modified for sportier performance at low speeds.

In newer cars (particularly the 2006 and 2007 G35 that I have driven as loaners) that have the same transmission, the programming causes the car this setting to drop down to 1st gear when the car comes to a stop, so you have to manually up-shift when moving out again.

I did notice in the 2009 G37 that I drove some weeks back, that they now have a "DS" setting ... this apparently is a Sport mode that has different shift points, and behaves more like the programming on my 2003 M45.

Z

[EniGmA1987]

Why would VDC have any effect on MPG under normal driving conditions?

I dont know. But I notice that when it is off, I get worse milage. Every once in a while, when I turn it on or oof, I can feel the car change in how it drives when the VDC kicks on/off. So again, I have no idea why it affects milage, I just know that I can feel it and that the numbers done lie.

[GJEMD]

there have been several threads regarding poor fuel efficiency in the M35.I suspect a major contributor is Wt /HP. there is a tipping point where lower displacement and hp just can't do the work as efficiently. Another factor is the M45 has the advantage of tremendous torque that's more efficient on slight changes in the grade of the road.

[83wildcat]

I have a 2006 M35X. During the winter I was getting a consistent 17.3 city mpg (~ 28 mph on the trip computer), with no difference between 87 octane and 91 octane. Now the weather has been getting warmer my mpg has improved to 18 - 19 mpg city. I think the improvement is because I'm no longer using my heat (which uses the A/C) and it hasn’t gotten hot enough to turn on the A/C. It will be interesting if I drop back down to 17 mpg in the summer when I run the A/C.

Highway is around 23 - 24 mpg.