Gas Mileage

[MM...Good]

I was wondering what sort of gas mileage folks are getting from their M's. From memory, my 2006 M35X would get around 18 or 19 in town and 24 on the highway with summer blend gas - usually 91 or higher octane. My winter mileage always sucked - around 15 in town.


I just drove my new to me (my son's daily driver) 2007 M35X 250 miles round trip- all highway- and the best I could get was 22. He tells me its been around 15 in town since we got it in early August. He doesn't have a lead foot so I'm not sure why the mileage is so low. It has brand new plugs and the air filter is clean. PCV valve maybe?

[Ilya]

Nature of the beast. This car isn't efficient. My 07 M35x that I used to have got the same mileage as you and I was anal retentive about maintenance, tire pressures, etc. (changed my filters, PCVs, etc. before they were do). My M56x gets about 17/22 as well which is interesting considering 2.1L more of engine and 2 more cylinders...however it does have a 7AT and not a 5AT.

Look into 'hypermiling' if you want to know what people do to squeeze every last bit of fuel out of their cars.

[gavnator]

Just made a run from North Georgia to Rotonda West Florida to see my brother. 1100 miles round trip. I got 23 mpg down and back. For this car, 23 mpg is good as it is geared for performance, NOT for milage. I have never gotten better than 23 mpg in my 06' M35x. 91,000 on the clock. I use nothing but top tier 93 octane and have never had a performance issue. 18 mpg around town.

[DS2009m35x]

2009 M35x. Long road trip down south I got 24. Locally I usually take it easy, but enjoy putting my foot into it occasionally. Results are a very consistent 18.5 in mixed local and highway driving. Winter can be slightly worse. I have tested many times using regular versus mid and high and have measured no discernible difference in MPG between the grades.

[MM...Good]

Yeah - I get that 7sp vs. 5sp. transmission. My G37 convertible weighs every bit as much as the M35X and gets a bit over 20 with mixed use daily driving with the 7sp. I just thought the '07 M would be similar to my old car but it's definitely lower.

[Larz]

My 07 M35 with the 5 sp gearbox was able to teach about 22 mpg on long motorway trips with cruise control. My 09 M35 with the 7 sp gearbox reaches 24 mpg on the motorway. Both cars can only manage 16-17 on surface roads in stop and go traffic. The only difference between the two cars is the gearbox, and also the 09 has the HR engine with dual intakes. Both cars were solely 93 octane fuel and I am anal about air filters, PCV, and fluids. Both cars use only Mobil-1 5w30 oil with changes every 4 months regardless of mileage (usually 3-4,000 miles).
These cars were NOT designed to be low cost in any other way, so below average large sedan mpg should be expected as well.

[LIBRILZ]

FWIW My M45 the best I usually get on the highway is 22MPG lol

it sucks and all going from 25-29 MPG in my I30 to 21-22 in the M45, but oh well

[kydegan]

My 06 M35 on a 1300 mile round trip averaged 23 on 87 octane. Couple of things I noticed. NC/SC gas yielded at least 1.5 mpg better than FL gas. I have no idea why. Second thing keep it at 76-77 fuel mileage is good, get to 80 and falls off a proverbial cliff. Lost 2-3 mpg at 80 or more.

[MM...Good]

My 06 M35 on a 1300 mile round trip averaged 23 on 87 octane. Couple of things I noticed. NC/SC gas yielded at least 1.5 mpg better than FL gas. I have no idea why. Second thing keep it at 76-77 fuel mileage is good, get to 80 and falls off a proverbial cliff. Lost 2-3 mpg at 80 or more.

+1 on the 80 mph & above. The speed limit was 75 on my 2 hour drive and I kept it around 80 so that makes sense. Next time I'll keep her at 75 and see how she does - assuming I don't get run over!

[Larz]

Generally speaking, the Dept of Energy did a study to determine, on average, the decrease in mpg from 55 mph and above. There is a website with a free calculator that lets you input your car's mpg at 55 + the miles driven daily + your local cost per gallon of fuel. http://www.mpgforspeed.com/
Each engine has a specific range of RPM where it operates at maximum efficiency and driving outside this range contributes to lower mpg. Also your engine uses about 40% of it's energy just pushing the car against the air to move it forward.
For me, I get 24mpg at 55, 20mpg at 70, and 17mpg at 80. I lose 7 miles per gallon by driving at 80mph instead of 55mph. Per the study, the average engine is nearly 30% LESS efficient at 80mph Vs 55mph.

[LIBRILZ]

Generally speaking, the Dept of Energy did a study to determine, on average, the decrease in mpg from 55 mph and above. There is a website with a free calculator that lets you input your car's mpg at 55 + the miles driven daily + your local cost per gallon of fuel. http://www.mpgforspeed.com/
Each engine has a specific range of RPM where it operates at maximum efficiency and driving outside this range contributes to lower mpg. Also your engine uses about 40% of it's energy just pushing the car against the air to move it forward.
For me, I get 24mpg at 55, 20mpg at 70, and 17mpg at 80. I lose 7 miles per gallon by driving at 80mph instead of 55mph. Per the study, the average engine is nearly 30% LESS efficient at 80mph Vs 55mph.

Strange considering you have the 7-speed transmission

that is my biggest gripe with the M45, if it had a 7-speed it would've been a much better car

[rabi_lj]

I live in montreal. if I drive on highway at 85 km/hr, I can hit 8-8.5L/100km. Yet in city driving, it goes up to 17L per 100km. I did everything to improve the MPG, still the city driving is a nightmare for M35X.