Welcome to the North American Subaru Impreza Owners Club Thursday March 28, 2024
Home Forums Images WikiNASIOC Products Store Modifications Upgrade Garage
NASIOC
Go Back   NASIOC > NASIOC Subaru Models > Impreza Forum

Welcome to NASIOC - The world's largest online community for Subaru enthusiasts!
Welcome to the NASIOC.com Subaru forum.

You are currently viewing our forum as a guest, which gives you limited access to view most discussions and access our other features. By joining our community, free of charge, you will have access to post topics, communicate privately with other members (PM), respond to polls, upload content and access many other special features. Registration is free, fast and simple, so please join our community today!

If you have any problems with the registration process or your account login, please contact us.







* As an Amazon Associate I earn from qualifying purchases. 
* Registered users of the site do not see these ads. 
Reply
 
Thread Tools Display Modes
Old 11-16-2012, 11:48 AM   #2351
flyboy1100
Scooby Guru
 
Member#: 314216
Join Date: Mar 2012
Location: ND
Vehicle:
2012 2.0i Sport 5MT
DGM

Default

Quote:
Originally Posted by pxpaulx
Please do us all a favor and keep the crazy back and forth confined to the other thread...don't worry, we are all reading it for one reason or another.
Exactly
* Registered users of the site do not see these ads.
flyboy1100 is offline   Reply With Quote
Sponsored Links
* Registered users of the site do not see these ads.
Old 11-17-2012, 06:43 AM   #2352
Penguin44
Scooby Newbie
 
Member#: 315883
Join Date: Apr 2012
Chapter/Region: E. Canada
Vehicle:
2012 IMPREZA
Silver

Default

Latest fill up.

625.3km 100% city. 8.6l/100km actual. Avg temps 3c about to do first oil. Total mileage 6903.6km

Pretty close to the suggested numbers and that's fine with me! When it was a little warmer I was getting about 8 so not too shabby.
Penguin44 is offline   Reply With Quote
Old 11-17-2012, 06:59 AM   #2353
Gev_ISMwrx
Scooby Newbie
 
Member#: 338122
Join Date: Nov 2012
Chapter/Region: SCIC
Location: Los Angeles, CA
Vehicle:
2012 Impreza WRX
Ice Silver Metallic

Default

Tuned on 91 with a 3" cattless downpipe and intake I'm getting about 15/22
Gev_ISMwrx is offline   Reply With Quote
Old 11-17-2012, 09:13 AM   #2354
Irongrave
Scooby Newbie
 
Member#: 325040
Join Date: Jul 2012
Chapter/Region: South East
Location: Florence SC
Vehicle:
2017 Forester XT
LPB

Default

Getting 27.3 and just over 2500 on the odometer miles almost pure city driving.
Irongrave is offline   Reply With Quote
Old 11-17-2012, 12:14 PM   #2355
Haunty
Scooby Newbie
 
Member#: 319378
Join Date: May 2012
Chapter/Region: MWSOC
Location: West Central MN
Vehicle:
2012 2.0i Sport Ltd.
Satin White Pearl

Default

I lost about 3mpg with the switch to winter gas I think, like night and day. Other than that, I haven't noticed any change in average mpg after almost 10,000 miles.
Haunty is offline   Reply With Quote
Old 11-17-2012, 12:23 PM   #2356
tomwi53092
Scooby Newbie
 
Member#: 316315
Join Date: Apr 2012
Chapter/Region: MWSOC
Location: Mequon, WI
Vehicle:
2012 Imp HB/Prem/CVT
DCP

Default

Quote:
Originally Posted by Haunty View Post
I lost about 3mpg with the switch to winter gas I think, like night and day. Other than that, I haven't noticed any change in average mpg after almost 10,000 miles.
My mileage immediately dropped 3-4 mpg on the last fillup 3 weeks ago. Temperature and weather was the same before and after. Funny thing was, it was only a 6 gallon fillup, so most of the gas in the tank was the older gas. All brand-name gas. Curious.
tomwi53092 is offline   Reply With Quote
Old 11-17-2012, 12:56 PM   #2357
sgoldste01
Scooby Specialist
 
Member#: 322264
Join Date: Jun 2012
Chapter/Region: Tri-State
Location: Webster, NY
Vehicle:
2012 Impreza Sp 5sp
Obs Blk Prl/Drk Gray Mtl

Default

I just installed snow tires on my Impreza, and then immediately topped off my gas tank and zeroed my odometer so that I can see how much effect the snow tires have on MPGs.
sgoldste01 is offline   Reply With Quote
Old 11-17-2012, 01:43 PM   #2358
auskip07
Scooby Specialist
 
Member#: 315643
Join Date: Apr 2012
Chapter/Region: South East
Location: Atlanta Ga
Default

ok i really think it has more to do with the fact that the car is running rich for longer warming up than any winter fill vs summer fill.
auskip07 is offline   Reply With Quote
Old 11-17-2012, 04:33 PM   #2359
Penguin44
Scooby Newbie
 
Member#: 315883
Join Date: Apr 2012
Chapter/Region: E. Canada
Vehicle:
2012 IMPREZA
Silver

Default

Quote:
Originally Posted by auskip07
ok i really think it has more to do with the fact that the car is running rich for longer warming up than any winter fill vs summer fill.
Yup I tend to agree on that. I can see that the rpm are staying higher for longer during my drive in that warm up. But overall its not a huge drop and was expected as it get colder.
Penguin44 is offline   Reply With Quote
Old 11-18-2012, 01:39 AM   #2360
chicagocpo
Scooby Newbie
 
Member#: 315470
Join Date: Apr 2012
Chapter/Region: NESIC
Location: Massachusetts
Vehicle:
2012 Impreza LTD
Marine Blue Pearl

Default

Quote:
Originally Posted by Penguin44 View Post
Yup I tend to agree on that. I can see that the rpm are staying higher for longer during my drive in that warm up. But overall its not a huge drop and was expected as it get colder.
How about the first law of thermodynamics? I'm thinking about reduced mileage in cold weather AFTER the car warms up, that would have greater relative effect on longer trips. "Heat and work are forms of energy transfer." So, colder temperature would mean more energy used to maintain the engine at running temperature, leaving less for the "work" of moving the car once it got there.

Maybe there is a physicist out there who could comment on this?
chicagocpo is offline   Reply With Quote
Old 11-18-2012, 06:11 AM   #2361
sgoldste01
Scooby Specialist
 
Member#: 322264
Join Date: Jun 2012
Chapter/Region: Tri-State
Location: Webster, NY
Vehicle:
2012 Impreza Sp 5sp
Obs Blk Prl/Drk Gray Mtl

Default

^^ I don't think this is the valid explanation. I think it's simply that an engine (or furnace, or boiler, or kerosene heater, or oven, etc.) work most efficiently when they're hot. So the warm-up time is when our cars get crappy MPGs. Once they warm up, they're fairly efficient.

In the winter, it takes longer for the engine to warm up because the starting temp is lower, and because the air blowing into the engine is colder, so it takes longer for the engine to reach max efficiency. Add to that the winter blends of gas, and you take a double-whammy on your MPGs.
sgoldste01 is offline   Reply With Quote
Old 11-18-2012, 09:22 AM   #2362
stevehnm
Scooby Specialist
 
Member#: 329526
Join Date: Aug 2012
Chapter/Region: SWIC
Location: Ground Control
Vehicle:
2013 Impreza Spt cvt
Silver

Default

There are actually several factors why fuel economy suffers in the winter. The biggest, depending on your driving style, is that cold air is just more dense than warm air. That means several things are happening. For one, you are pushing more air - up to 10% more. Another reason is that as a certain volume of air comes into the engine, in the winter that has more mass so there is more fuel put in to compensate. Then, fluids are more viscous (thicker), which increases the power drag - things like transmissions and differentials that don't have cooling "systems" are more of a drag. Tires have less pressure so there is more rolling resistance.

The other reason, which may be major depending on your driving habits, is that people tend to warm their cars up more in the wintertime and take more shorter trips instead of walking or riding a bike, and it does take longer for all of the engine to warm up to optimum temperature in the winter (even though the gauge may say it's already warm).

So, the answer is: It depends...
stevehnm is offline   Reply With Quote
Old 11-18-2012, 09:56 AM   #2363
auskip07
Scooby Specialist
 
Member#: 315643
Join Date: Apr 2012
Chapter/Region: South East
Location: Atlanta Ga
Default

Quote:
Originally Posted by chicagocpo View Post
How about the first law of thermodynamics? I'm thinking about reduced mileage in cold weather AFTER the car warms up, that would have greater relative effect on longer trips. "Heat and work are forms of energy transfer." So, colder temperature would mean more energy used to maintain the engine at running temperature, leaving less for the "work" of moving the car once it got there.

Maybe there is a physicist out there who could comment on this?
except for the fact that colder air produces more power because its more dense as said above. I believe that the engine may pour more fuel but not much. What ends up happening is the car leans out. (this is safe in colder weather) Same principle behind water injection. Or the timing adjusts

Last edited by auskip07; 11-18-2012 at 10:16 AM.
auskip07 is offline   Reply With Quote
Old 11-18-2012, 11:13 AM   #2364
ST Eye
Scooby Specialist
 
Member#: 73068
Join Date: Oct 2004
Location: MD
Vehicle:
2008 STI Boost Wagon
2014 Honda Accord Hybrid

Default

When the car is cold (and it is colder longer in the winter time) the engine is in open loop. While in open loop fuel is dumped into the engine at a higher rate than when in closed loop. This could add to the larger consumption during the colder months.
ST Eye is offline   Reply With Quote
Old 11-18-2012, 11:18 AM   #2365
tomwi53092
Scooby Newbie
 
Member#: 316315
Join Date: Apr 2012
Chapter/Region: MWSOC
Location: Mequon, WI
Vehicle:
2012 Imp HB/Prem/CVT
DCP

Default

Quote:
Originally Posted by chicagocpo View Post
How about the first law of thermodynamics? I'm thinking about reduced mileage in cold weather AFTER the car warms up, that would have greater relative effect on longer trips. "Heat and work are forms of energy transfer." So, colder temperature would mean more energy used to maintain the engine at running temperature, leaving less for the "work" of moving the car once it got there.

Maybe there is a physicist out there who could comment on this?
When detonation occurs, some of the energy is converted to expansion, which powers the cylinders. Most of the energy is converted to heat, which is waste energy, doesn't contribute to powering the car. It doesn't matter if it's 32 degrees outside or 100 degrees, detonation will produce mostly waste heat in excess of what's needed to maintain the engine at optimal running temperature. So, no, in cold weather, the chemical reaction doesn't change to produce more heat and less expansion. The gas isn't "smart" that way.

Mostly, in cold weather, you have the issues that others have pointed out: fluids are thicker and take much longer to warm up, so have more resistance and take more power to move engine parts in contact with the fluids.

And then there's the winter gas issue:
According to this, winter gas has more butane, which has less energy, resulting in up to 1.7% lower energy output.

(Not a physicist).
tomwi53092 is offline   Reply With Quote
Old 11-18-2012, 11:34 AM   #2366
Commander Keen
Scooby Specialist
 
Member#: 319157
Join Date: May 2012
Chapter/Region: MAIC
Vehicle:
2012 Impreza 4DR 5MT

Default

As long as the engine is running at operating temperature, it doesn't make much of a difference whether the excess heat is shed through the block or radiator.

The problem I'm seeing is that the engine sometimes struggles to maintain operating temperature, which definitely has an impact on efficiency.

Most of the engine's power goes towards moving the air you drive through. In the winter, this air becomes more dense and provides more resistance.
Commander Keen is offline   Reply With Quote
Old 11-18-2012, 11:49 AM   #2367
stevehnm
Scooby Specialist
 
Member#: 329526
Join Date: Aug 2012
Chapter/Region: SWIC
Location: Ground Control
Vehicle:
2013 Impreza Spt cvt
Silver

Default

Quote:
Originally Posted by Commander Keen View Post
The problem I'm seeing is that the engine sometimes struggles to maintain operating temperature, which definitely has an impact on efficiency.

Most of the engine's power goes towards moving the air you drive through. In the winter, this air becomes more dense and provides more resistance.
If the thermostat is working correctly the engine should stay at operating temperature without any problem.

Moving the air (wind resistance) is in fact generally the largest factor in fuel consumption rate, once you're warmed to equilibrium. If it's 50% (and that will be determined by the aerodynamics of the vehicle) and density is increased by 10%, you can expect your fuel consumption to increase by 5%, all other things being equal.

As far as colder air intake, the increased available power from the colder, more dense mixture going into the combustion chambers is offset, at steady state, by needing less weight on the accelerator pedal. It's the change in density, not temperature, that affects the available power.
stevehnm is offline   Reply With Quote
Old 11-18-2012, 12:13 PM   #2368
Commander Keen
Scooby Specialist
 
Member#: 319157
Join Date: May 2012
Chapter/Region: MAIC
Vehicle:
2012 Impreza 4DR 5MT

Default

Quote:
If the thermostat is working correctly the engine should stay at operating temperature without any problem.
The thermostat is working fine, but blowing cold air over the heater core can cool down a warmed up engine, or prevent an idling engine from ever fully warming up.

If you have a scan tool, see for yourself. The blue light going out only indicates 120F.

Quote:
If it's 50% (and that will be determined by the aerodynamics of the vehicle) and density is increased by 10%, you can expect your fuel consumption to increase by 5%, all other things being equal.
Aero losses increase exponentially with speed so that percentage will change with speed as well. Your 50% figure is true of most cars doing 25 MPH and rises with speed.
Commander Keen is offline   Reply With Quote
Old 11-18-2012, 12:44 PM   #2369
stevehnm
Scooby Specialist
 
Member#: 329526
Join Date: Aug 2012
Chapter/Region: SWIC
Location: Ground Control
Vehicle:
2013 Impreza Spt cvt
Silver

Default

I have a Scangauge so will check that. I think you are probably correct in your generalization about "most cars" and 25 mph, but I'm not sure about the smaller much more aerodynamic cars like the Impreza. It might be 40 or so, due to the extra differential
stevehnm is offline   Reply With Quote
Old 11-18-2012, 05:30 PM   #2370
Haunty
Scooby Newbie
 
Member#: 319378
Join Date: May 2012
Chapter/Region: MWSOC
Location: West Central MN
Vehicle:
2012 2.0i Sport Ltd.
Satin White Pearl

Default

I don't think it's that complicated. A 3mpg drop is quite a bit, and a 3 mpg drop right after a fill-up while the temperature remains the same between fill-ups, kinda makes me think it's winter blend gas.
Haunty is offline   Reply With Quote
Old 11-19-2012, 01:24 AM   #2371
nubsub
Scooby Specialist
 
Member#: 313575
Join Date: Mar 2012
Location: SF Bay Area, CA
Vehicle:
2012 Impreza 2.0i HB

Default

Quote:
Originally Posted by Haunty View Post
I don't think it's that complicated. A 3mpg drop is quite a bit, and a 3 mpg drop right after a fill-up while the temperature remains the same between fill-ups, kinda makes me think it's winter blend gas.
That's what I've noticed in mild California during my last two tanks. There has been a noticeable drop in mileage with no other significant changes.
nubsub is offline   Reply With Quote
Old 11-19-2012, 07:45 PM   #2372
hemophilic
Scooby Specialist
 
Member#: 301213
Join Date: Nov 2011
Chapter/Region: South East
Location: Raleigh, NC
Vehicle:
2012 Imp. Sp. Ltd.
Blue/Silver

Default

Cold temps... Bah...
330.3 miles. 13.04 gal.
27 mpg avg. 25.3 mpg actual.
23 mph avg.
9625 miles on ODO.
http://www.fuelly.com/driver/hemophilic/impreza
hemophilic is offline   Reply With Quote
Old 11-19-2012, 07:51 PM   #2373
jr0bb5
Scooby Specialist
 
Member#: 315353
Join Date: Apr 2012
Chapter/Region: NESIC
Location: MA
Vehicle:
2012 Impreza Sp Prem
5MT OBP/DGM

Default

Same here. I've easily dropped about 3 MPG within the past few weeks.
jr0bb5 is offline   Reply With Quote
Old 11-19-2012, 09:02 PM   #2374
stevehnm
Scooby Specialist
 
Member#: 329526
Join Date: Aug 2012
Chapter/Region: SWIC
Location: Ground Control
Vehicle:
2013 Impreza Spt cvt
Silver

Default

I monitored the water temperature via the Scangauge as the engine heated up this morning. When the interior of the vehicle was cold (at first) the engine would in fact slowly cool at stop lights. However, when the interior warmed up the Scangauge consistently read 182 to 184 deg F.
stevehnm is offline   Reply With Quote
Old 11-19-2012, 09:48 PM   #2375
ZionZR2
Scooby Newbie
 
Member#: 319990
Join Date: May 2012
Chapter/Region: TXIC
Location: Austin, TX
Vehicle:
2012 Imp Prm 5D CVT
Dark Grey Metallic

Default

I'm averaging 27.2 so far all my fill-up data available at:

ZionZR2 is offline   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
New Impreza owner, low mpg? stuffedcabbage Newbies & FAQs 36 08-28-2017 07:10 AM
2012 Impreza Reviewed - Whytecliff to Seymour brendan_mac Vancouver Impreza Club Forum -- VIC 16 12-23-2011 01:12 PM
NJ Impreza owners - sighting Dan G General Forum Archive 76 10-06-2000 12:24 AM
Md or Va Impreza owners - I have an Impreza related question. Snoopy General Forum Archive 1 06-05-2000 08:08 AM

All times are GMT -4. The time now is 02:35 AM.


Powered by vBulletin® Version 3.7.0
Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.
Powered by Searchlight © 2024 Axivo Inc.
Copyright ©1999 - 2019, North American Subaru Impreza Owners Club, Inc.

As an Amazon Associate I earn from qualifying purchases.

When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission
Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.