What's better for MPG - manual shifting, DS, or D
 

Hi Everyone:

I know the topic of MPG in the G35 has been discussed a lot here, and I've searched and read many of the postings.

One thing that I haven't been able to find, is a discussion of optimizing MPG given consistent driving conditions. Obviously I know that if you drive less agressively, keep your speeds as consistent as possible, etc., you'll get lower MPG. However, I'm wondering if I can increase my MPG by shifting myself using the paddles, keeping the revs between 2k and 4k, etc., versus letting the auto shift for me either in D, or DS mode.

My gut sense is that DS actualy gives me better mileage than D mode for most reasonably agressive driving because I don't have to hit the pedal all the way down to get it to down shift when I need to suddenly hustle. I feel like if I'm in 4th or 5th all the time when going 40mph or so, I'm getting worse MPG if I drive even slightly agressively.

Any thoughts and/or facts on this topic would be welcome. I love driving my G fairly agressively, and a lot of time, I just say 'to hell with the MPG', but other times when I'm not in the mood for agressive driving, with gas prices being where they are today in the NE, it does make a difference to the bottom line.

Thanks a lot
Tamir

DS is definitely going to get worse fuel economy.

It holds the gears longer at higher rpms. Also, it waits longer to lock up the TQ converter. And, it doesn't upshift as quickly after any decent acceleration, it'll hold the gear longer. Plus, it downshifts more aggressively when braking. All bad for gas.

My bet would definitely be just leaving the car in D.

Here's the simple explanation for rpms and fuel economy: The lower the better. The sooner you can get into higher gears, and the longer you stay there, the better fuel economy you get.

With computer controlled fuel injection cars, the computer is constantly trying to keep your air fuel ratio at stoich (about 14.7 to 1) in non-power enrichment mode (normal driving) and around 12.5 to 1 during PE mode (higher rpms and throttle settings). More air (higher rpms) equals more fuel equals worse fuel economy.

Basically, "lugging" the motor doesn't hurt (accelerating in 4th or 5th gear). I've actually read that your engine is most fuel efficient at low rpms at FULL THROTTLE (with the throttle body all the way open) as long as you're not in PE mode.

It's different than an old carb motor that you just dump fuel in when you hit the gas.

Bottom line: keep your foot out of the gas, leave it in D, you'll be the best off.

You can also watch your instant MPG meter in dash to see what behavior causes the mileage to go down. If I lived in a real flat area my freeway mileage would easily creep up to 26 or 27, but there are a lots of hills on freeway around here so it keeps my mileage in the 21-23 range. Interestingly I think my cruise control mileage in 70-75 range is better than 60-65mph.

My mileage tends to be better traveling 70-75 versus 60-65 as well. I wonder if the rpm range of 70-75mph allows for less pedal to climb hills?

D. In DS the G holds gears longer to promote better performance, and in M you're likely shifting at sub-optimal RPM and shift points.

Manual mode shifts give the best MPG if shifted properly.

Otherwise, stay in D. D is optimized for MPG/smoothness, DS is optimized for power

I honestly think it depends on how smooth you accelerate. I've been averaging slightly over 23mpg (in the G35S)! I noticed that no matter if I'm in the MT, D, or DS mode, it again, depends on how smoothe I accelerate. I also have been getting 375-380 on a full tank!

When I want to get good MPG.. I stick it in triptronic and keep tapping the shifter up so I can get to the next highest gear ASAP

2.5vq :D

D is your best option for best MPG

This is what I was thinking, but I'm wondering what the proper shifting interval is in M mode. Today I tried shifting between 2k and 4k every time, and keeping the revs in that range. It worked relatively well, but I still couldn't get above 18mpg. I'll try D and light driving for a full tank and see how it goes.

Thanks for all your replies.

Cheers
Tamir

Gas is around $4.70 here in CA. Three days ago, I tried to take it easy on my way to work. I mean really easy, may be the slowest/easiest going I have driven in my life. A total of 16 miles of driving (8 miles city and 8 miles freeway) with no AC. I got average of 26.8 MPG.


The next day I was late to work, and was cut off by a Scion, so hell broke loss and ate Scion for breakfast. I got only 12 MPG, average on the same exact rout and turns.


On my regular day, I usually get around 19.9 MPG

All of the above drivings were done in D

Define "properly" though. It's more likely that D is going to get it right better than you can.

In manual mode, I've found that I can shift into 5th (and hold 5th gear) sooner and longer than D would naturally. This "could" help fuel economy. But, in manual mode, even in 5th, the car takes longer before the TQ converter locks up, which would hurt fuel economy.

That, and every once in a while in manual, I forget to shift at the right time.

I'm betting you'd have a hard time being more efficient than just regular D.

I'd like to challenge someone to try though. Drive slowly in D for a week, then manual mode an compare average fuel economy for both times. Log it, chart it, get back to us.