Mustang GT Fuel Economy in Stop-n-go Driving

[mustang#16]

I started a new job 2 weeks ago that requires me to commute daily 25 miles each way in stop and go traffic (45 minutes ~ 60+ minutes each way). Previously, I worked from home and only drove my 2015 Mustang GT for pleasure, almost never in stop and go traffic.

Since I'm driving more (1,000 more miles per month), I switched from 93 octane to 87 octane gas to save money. The car runs fine on 87 here in the Dallas area with temps 100+ degrees (amazing for an 11.0:1 compression ratio!), however, I have noticed that the car doesn't accelerate quite as fast under full throttle. This is to be expected with a slight HP drop due to the lower octane, but it was noticeable. Definitely not a problem, however, as there was still plenty of power for any situation on the street.

The main reason for my post is how I've changed my driving style during my commute and the good fuel economy that I'm getting. Almost all of my commute time is stop and go driving in very heavy traffic. Rather than shift into each gear from a stop, I'll start in first, then at 2,600 RPM I'll shift into 3rd gear and, as soon as I can, I'll shift into 5th gear skipping 2nd and 4th gears. When I shift into 3rd and 5th, the RPMs drop to 1,000. I do this under the assumption that my fuel economy will be better than if I had not skipped 2nd and 4th gears and, frankly, I don't consider it fun constantly pressing a pedal and rowing a shifter in that kind of driving.

So, with the A/C running in 85 ~ 100+ temperatures and in mostly stop and go driving, I'm averaging 20 MPG per week (Mon-Fri) according to the fuel economy computer (reset at beginning of each week)! For that kind of driving, I think 20 MPG is excellent considering it's a 5.0L V8 Mustang. The engine has so much low-end power that the car has no trouble accelerating when skipping 2nd and 4th gears.

Sure, nobody buys a Mustang GT for fuel economy, and skipping gears is not all that fun, but when you're constantly stopping and going for about an hour each way every day, the economy savings sure add up and the leg and arm enjoy a little time off from pumping a pedal and stirring a shifter inbetween stops. FYI, I have the base suspension, 3.31:1 axle, and 19" wheels.

On weekends, I definitely enjoy winding up the engine and going through the gears! After almost 10 months of ownership and almost 8,000 miles, I'm really enjoying this car!

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[Blk2015GT]

Since I'm driving more (1,000 more miles per month), I switched from 93 octane to 87 octane gas to save money. The car runs fine on 87 here in the Dallas area with temps 100+ degrees (amazing for an 11.0:1 compression ratio!), however, I have noticed that the car doesn't accelerate quite as fast under full throttle. This is to be expected with a slight HP drop due to the lower octane, but it was noticeable. Definitely not a problem, however, as there was still plenty of power for any situation on the street.

The GT only loses 1% of hp dropping to 87, so about 4.5hp. I doubt any normal person could tell that from the old butt dyno.

What you're probably feeling more is the engine pulling timing to run the 87. But stop-and-go and full throttle are kind of oxymorons to begin with.

I run 87 and can't say I can tell a difference. The only room to put it to anywhere near full throttle around here is on and off ramps to the highway which I do very little highway driving unless absolutely necessary (keeps rock chips to a minimum too).

For daily driving 87 runs perfect and saves a good amount of money over the course of a year. Right now around here 93 is $.80/gallon more than 87. Even per fill-up that's $11-12 saved putting a full tank in (14-15 gallons lets say as the tank is 16). Over a year that could be $500 or more only filling up once per week. To me I'd rather spend the $500-550 on an extra mod rather than big oil.

 

[grumblin]

Good lord, I'm in DFW and I get 13.9 mpg. That's stop and go for miles from Hebron to 635 up and downmarsh, midway or Josey. But then I enjoy driving her... ;)

 

[Blk2015GT]

Yeh I only get 13mpg with 3000 miles on the car but that's all city driving and literally no highway. I don't think it's seen the highway yet.

I still think the mpg goes up a bit as the first few thousand miles are still kind of breaking in everything.

 

[mustang#16]

What you're probably feeling more is the engine pulling timing to run the 87. But stop-and-go and full throttle are kind of oxymorons to begin with.

Agreed re oxymorons. I should've said that my full-throttle acceleration occurred on a freeway onramp (Saturday afternoon).

I agree and know what you mean regarding retarding of the ignition timing as being responsible for the acceleration difference in what I'm feeling. I remember back in the day when I experimented with rotating the distributor on my old '71 Mustang Mach 1 351C and '72 Pontiac LeMans 350 to advance the timing and see the effect on engine performance. While 1% HP loss on 87 octane isn't much, I wonder if the 1% HP loss is consistent across the RPM range of the engine or just at the RPM where the engine makes peak HP? I noticed the difference between 93 and 87 octanes mainly above 5,000 RPM. Below that, it was not noticeable. I recall 87/93 octane impact being discussed at length in other posts on this forum so I don't want to recreate that here, if possible.

Thanks for the comment!

 

[mustang#16]

I still think the mpg goes up a bit as the first few thousand miles are still kind of breaking in everything.

Agreed. It will go up. I've noticed that it makes a big difference in economy in how aggressive one drives. Accelerate fast inbetween lights, it sucks gas. Accelerate easy inbetween lights, it will return respectable fuel economy.

I also don't know what affect a 3.73 vs 3.31 axle will have on economy. It will have some impact, I just don't know how much. I have the 3.31.

 

[mustang#16]

Good lord, I'm in DFW and I get 13.9 mpg. That's stop and go for miles from Hebron to 635 up and downmarsh, midway or Josey. But then I enjoy driving her... ;)

I'm driving up from the GP/Arlington area to Coppell. Any route you try to take, it's stop n go. Hwy 360, Hwy 161/Bush Tollway, or Loop 12 Walton Walker are all parking lots every day. I usually just take Belt Line Rd all the way up from I-20 past 635. It's a consistent 55 minutes. Lots of traffic lights (some requiring 2 or 3 light cycles to get thru) but I'm never late that way.

I get 20 MPG taking Belt Line Rd every day.

 

[Socalmustang]

How in the (insert expletive here) do you get 20mpg in stop and go traffic?:eye bulge:

In those kind of conditions, at best I get around 15.

 

[mustang#16]

How in the (insert expletive here) do you get 20mpg in stop and go traffic?:eye bulge:

In those kind of conditions, at best I get around 15.

Almost all of my commute time is stop and go driving in very heavy traffic. Rather than shift into each gear from a stop, I'll start in first, then at 2,600 RPM I'll shift into 3rd gear and, as soon as I can, I'll shift into 5th gear skipping 2nd and 4th gears. When I shift into 3rd and 5th, the RPMs drop to 1,000.

I'll make a video next week of how I drive and show the avg MPG results at the end of the drive.

 

[Socalmustang]

I have the PP with the 3.73 gear ratios, but I wouldn't assume that makes too much of a difference.

I'm gonna try skip shifting, as I rarely ever do it and see if my mpg goes up....just out of curiosity, gas isn't a big deal to me but it would be cool to see a difference

 

[madweazl]

I average 12.9 in northern VA traffic.

 

[ktapia]

I average 12.9 in northern VA traffic.

Amen Brotha. :doh:

 

[Teezlr]

Yeah, 10-13 mpg in real stop and go traffic sounds about right, like where your average mph is 14-16 mph

 

[Khyber]

17.5-18.3 here around town in 35, 40, 45 mph zones. if I get to the 55mph zone usually can get it up to high 18s.

 

[jrt6]

I'm averaging 17ish on my commute to work. It's on side streets and then highway for about last 3/4ths the way there. I'm usually at 17.5-17.6 according to the car. My average on Fuelly is 16.4.

I shift up at around 2,000-2,500 and coast to a stop as much as I can.

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