Gas mileage has went downhill...

[StingerNYC]

I have been noticing recently that my miles per gallon has dropped significantly. I have taken 3 trips from NYC to Chicago in the stinger. The first was in June, and then again in October. In those instances my gas mileage was consistent at 26-27mpg. A couple weeks ago I made the same trip and i was averaging 21-23mpg. Never higher. The same span of highway in both directions. I always use 93 octane. I haven't changed anything on my car since the October trip. What could cause this drastic of a drop?

I do have a JB4, intakes and a catback, but all were on my car prior to October and did not seem to affect it then. I disconnected the JB4 for the return trip and it still maintained an average of 22mpg.

Any ideas?

 

[StingerNYC]

To add, I did make one change since October. I got new wheels/tires, but they are the exact same size and weigh less, so I do not see how that could affect it negatively.

 

[BlaydeX15]

Winter mileage sucks, I always expect to see a 15-20% drop in fuel economy between summer and winter. Road conditions, fuel composition, colder air, colder starts, tire pressure or the tire itself, if you changed it, etc. They all contribute to making it worse.

Some more info on why: Fuel Economy in Cold Weather

Edit: As for changing your wheels/tires, the weight might not offset the other properties of the tire. New tires might have a higher rolling resistance, a lower recommended pressure, etc.

 

[StingerNYC]

Interesting, but that doesn't seem to explain all of it. In October it was 60-70 degrees and during the last my trip in December it was in the 40s. On the link you shared it showed a 12% decrease for 57 degree temperature change.

Maybe it could be the tire. I went from the stock Pilot Sports to Pilot Sport A/S3+. I use the same air pressure.

 

[sting me]

Winter gas sucks. This is unfortunately common.

I'm pretty sure AS3+ are less sticky than PS4, so I doubt the tires are the issue. I'd check your alignment as well.

 

[nhcowboy28]

Interesting, but that doesn't seem to explain all of it. In October it was 60-70 degrees and during the last my trip in December it was in the 40s. On the link you shared it showed a 12% decrease for 57 degree temperature change.

Maybe it could be the tire. I went from the stock Pilot Sports to Pilot Sport A/S3+. I use the same air pressure.

Tires are the key.

For example. In my exploder, city mpg (actual was 19) on stock Hankook’s.

Put on Bridgestone Duelers... immediately dropped to 12-13.

“Grip kills MPG baby”

 

[Waynerm002]

I don't think the AS tires are stickier than the Summer tires. It's most likely the winter gas gas blend. The best mileage I have ever gotten was using pure gas, they have a few of those stations close to the dealer I bought the car from so when I go out there, I tend to fill up there. I have seen 385 miles out of a tank using pure gasoline.

 

[StingerNYC]

Thanks for the input. Hopefully it is only the winter blend gas. I will know for sure in the spring.

 

[Sabz]

Yea my mileage blows too in the winter... I average like 17 all the time ...

 

[MerlintheMad]

I thought I saw a slight drop in mpg when I put my Nitto Motivo UHP A/S tires on; maybe one to two mpg less. Does Costco do a winter blend? I haven't seen any drop in mpg aside from my MO of letting the car idle a lot longer to start warming the engine oil and trans up before I roll.

 

[StingerNYC]

One thing I did notice is that the turbos were activating boost while cruising at anything above 70. The rpms were high enough that both the gauge and the jb4 app showed boost. I think it was 2 psi. Maybe the winter gas cause rpms to be high enough that the car needed boost to maintain speed? It showed boost constant unless going down hill.

 

[SKStinger]

One thing I did notice is that the turbos were activating boost while cruising at anything above 70. The rpms were high enough that both the gauge and the jb4 app showed boost. I think it was 2 psi. Maybe the winter gas cause rpms to be high enough that the car needed boost to maintain speed? It showed boost constant unless going down hill.

Was it windy? It's also a major factor in fuel economy, a head wind will dramatically alter your fuel economy between trips. You talk about temperature above but what about wind speed/direction? A headwind may also be why you saw boost over 70.

 

[eflyguy]

I think there are also variations in "winter blend" by state, making it worse in some places.

 

[Jimmer]

I noticed since I've been running in Smart mode, my mpg has gone noticeably up:. 22.5 MPH today purely in Smart mode. Since filling up, it's gone from 15.9 after the first 100 miles driving in comfort, to sitting now at 18.9 at the 200 mile mark after switching to Smart at the 100 mark.

 

[MerlintheMad]

I noticed since I've been running in Smart mode, my mpg has gone noticeably up:. 22.5 MPH today purely in Smart mode. Since filling up, it's gone from 15.9 after the first 100 miles driving in comfort, to sitting now at 18.9 at the 200 mile mark after switching to Smart at the 100 mark.

That must mean that your typical driving mode is Eco. Because that is what Smart defaults too unless you accelerate "spiritedly". If you get on it all the way, Smart switches to Sport, albeit very briefly.

 

[Jimmer]

That must mean that your typical driving mode is Eco. Because that is what Smart defaults too unless you accelerate "spiritedly". If you get on it all the way, Smart switches to Sport, albeit very briefly.

A lot of city driving. A lot of lights. I punch it when I can but to and from work is so congested.

 

[TwinSnails]

I thought I saw a slight drop in mpg when I put my Nitto Motivo UHP A/S tires on; maybe one to two mpg less. Does Costco do a winter blend? I haven't seen any drop in mpg aside from my MO of letting the car idle a lot longer to start warming the engine oil and trans up before I roll.

They all winter blend depending on region, but yes they blend. NC a year ago had stopped blending because it wasn’t needed here.

 

[eflyguy]

The change is made to all fuel delivered to the depot from where it is distributed locally. Once it starts in your area, every station has it (although it isn't an overnight switch due to the volume of inventory and gradual re-supply from pipelines).

 

[rocket23]

My gas mileage sucks!!Course I have a hemi foot, damn thing is like an on/ off switch!!!

 

[Karl Davlin]

GT2 AWD w/no mods cruising mostly at 75MPH with a nice tailwind... Just got of the highway and snapped a picture. So, actual mileage is probably around 29MPG. By contrast, my last fill-up was only 23.77MPG (actual) with about 80% highway.