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Winter Impact on Fuel Economy and Mitigation

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Start with XtremeRevolution’s http://www.cruzetalk.com/forum/27-fuel-economy/5387-how-get-better-fuel-economy.html. Next, understand that a seasonal drop of 2-10% in fuel economy is very common in the winter. Below I have listed several reasons why and methods to reduce their impact.

1. Winter Gasoline, at least in the US, has about 2% fewer BTU than summer gasoline. There is nothing the average driver you can do about this. This also sets the lower level of reduced fuel economy at 2%.

2. Motor oil is thicker in low temperatures. You can work around by keeping your car in a heated garage, using an oil pan or engine block heater. Short trips in the winter are really hit hard by this additional friction within the engine.

3. Warming up the car by idling before driving. This isn’t required for the Cruze and wastes fuel. While the car idles, it’s getting zero MPG. You can start driving as soon as your RPMs stabilize after starting the car. You don’t have to wait until the RPMs drop to the 700-800 RPM idle, just keep the engine speed down. I keep my engine speed below 1500 RPM (turbo spool up start) for at least the first minute of driving.

4. Clear frost, ice, and snow off your car before starting the car (see #3). All three reduce visibility unless cleared and scraped from all windows. Brush off snow buildup from the hood, roof, and trunk of your car. Snow buildup decreases fuel economy by adding both weight (low speed) and air drag (high speed) to the car. In some jurisdictions (New Hampshire is an example), you are required by law to remove snow from car’s hood, roof, and trunk before driving. Don’t forget to clear your headlights, fog lights, and taillights. Remove ice buildup from the wheel wells as well. Be careful when scraping around the wiper blades as you can damage the rubber inserts with your scraper. I know, I've damaged mine on past vehicles. Clear any ice buildup from the wiper blades, arms, and pivot points.

5. Loss of Daylight Savings Time. As strange as this sounds, westbound afternoon congestion hours actually start an hour earlier by the clock in the winter than they do during the summer. For example, if your afternoon congestion starts at 4 PM in the summer it will start as early as 3 PM in the winter, even on a dry road. This is because the sun is that much lower and people start slowing down up to an hour earlier, which leads to earlier congestion. You can mitigate this by finding a different westbound route home. For example, I work in Aurora, CO (southeast of Denver) and have to get to C-470 and Santa Fe on the southwest side of Denver. In the summer I can use C-470 with no problems because the sun is high enough to not impact driver visibility. C-470 snakes north and south of due west, which means in the winter the sun is low enough at 3 PM that there are parts of C-470 that are driving directly into the sun. Very few drivers keep their windshields clean on the inside so they end up slowing down at 3 PM instead of 4 PM. Find an alternate route. I use Bellevue in the winter, which even with stoplights provides a much more consistent speed (improved MPG) than C-470. At no point do I ever drive directly into the sun.

6. Snow and Slush on the roads adds significant friction that doesn’t exist on a dry road. Water also adds friction, but not as much. You can reduce this friction by staying in the tracks that people in front of you have created. This does, however, reduce your stopping ability. The friction from snow and slush helps you slow down faster without skidding.

7. Plan your trips to for the middle part of the day, which tends to be the warmest. Also, plan your route to use predominately right turns and drive far enough to fully warm up the engine before your first stop. A warm engine gets better fuel economy and right turns require less idling.

8. Slow down. Not only does this improve fuel economy but it also gives you more time to react to other drivers and obstacles on the road.

9. Consider covering the lower grill of your Cruze. The ECO trims do this automatically when it’s cold by closing the louvers even at low speed.

10. Practice mild hyper-miling techniques year round. In the winter you want to be smooth to improve both vehicle control and fuel economy. This must be muscle memory for it to work.

11. During the warmest part of the day and after the car has been driven enough to warm up the tires, boost your tire pressure as high as you are comfortable but not over max sidewall. This will keep the tires from underinflating overnight. Use your TPMS to ensure all four tires are within a pound of each other to improve handling.

12. Winter air is denser, which has both negative impacts at highway speeds and positive impacts during low speed acceleration by adding additional air pressure for the engine to work with. About the only thing most of us can do with this is enjoy the cold and take up a winter sport of some sort.

13. Don't heat the cabin until the car's temperature needle is to the 1st quarter mark. You can get heat sooner, but at the expense of fuel economy. Remember, a warm engine is more efficient. If you need to run the defroster, select recirculate to avoid pulling in more cold air. Many cars select recirculate automatically when using the defroster but I don't know if the Cruze is one of them.


For a rundown from CleanMPG.com, try A Hybrid Owner’s winter survival guide - CleanMPG Forums.

Feel free to add to this list and discuss/shoot down my observations gleaned from over 25 years of tracking my MPG in multiple vehicles. Also, I'd like to thank various members of CruzeTalk who gave me some of these ideas that I hadn't previously figured out.
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· Administrator, Resident Tater Salad
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Good tips. I never really thought about #5, but come to think of it, it's definitely true. Then again, DC traffic never really makes sense to me.

Re: 13. Recirculated air contains moisture from your breath. While it may produce heat faster by not pulling in outside air, soon your windows will start fogging up anyway. If the temp outside is below 32-40 (whatever the Cruze stops running the AC compressor at), keep the recirculate function off.
 

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Good tips. I never really thought about #5, but come to think of it, it's definitely true. Then again, DC traffic never really makes sense to me.

Re: 13. Recirculated air contains moisture from your breath. While it may produce heat faster by not pulling in outside air, soon your windows will start fogging up anyway. If the temp outside is below 32-40 (whatever the Cruze stops running the AC compressor at), keep the recirculate function off.
Had an interesting time over the weekend with 4 people in my car including myself. Temperatures were 20-25 degrees F, and I couldn't keep the car from fogging up. The best setting that actually de-fogged all of the windows including the rear was to set the car to defroster mode with the recirculate function on. I believe this causes the A/C compressor to run for defroster function, which gradually keeps removing moisture from the air inside the car.
 

· Administrator, Resident Tater Salad
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Had an interesting time over the weekend with 4 people in my car including myself. Temperatures were 20-25 degrees F, and I couldn't keep the car from fogging up. The best setting that actually de-fogged all of the windows including the rear was to set the car to defroster mode with the recirculate function on. I believe this causes the A/C compressor to run for defroster function, which gradually keeps removing moisture from the air inside the car.
Huh, interesting. Most cars just cut it out entirely below a certain temp. I've had that same thing happen on others, and it will drive you bonkers.

That means that some thought really went into the climate control system on this car - it's basing the compressor operation off either an evaporator temperature sensor or intake air temp sensor vs just ambient temp. Learn something cool about this car every day.

Well, statement retracted!


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Discussion Starter · #6 ·
Good tips. I never really thought about #5, but come to think of it, it's definitely true. Then again, DC traffic never really makes sense to me.
The westbound rush hour issue hit home to me hard this fall when we switched from DST to Standard time. I wouldn't have thought of it either had I not actually experienced it.
 

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11. During the warmest part of the day and after the car has been driven enough to warm up the tires, boost your tire pressure as high as you are comfortable but not over max sidewall. This will keep the tires from underinflating overnight. Use your TPMS to ensure all four tires are within a pound of each other to improve handling.
Inflation pressures for tires are determined based on the tire being cold. That includes the max pressure given for the tires. The fact that tires heat up when rolling is part of the equation, so when the hot tire reads above the max pressure (which is based on a cold tire) it is still within a safe operating range. The max pressure is safe as long as it is checked when outside temperatures warm up significantly since it was last checked.

It works the same way if you want to stay with lower pressures on the door tag. Set the pressure cold. That way the pressure does not drop because of cold temps. It will warm up by about 2 lbs when rolling.
 

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Number 3 kinda contradicts 4. If I were to drive my car it would take 5 minutes to generate any form of heat, which means the inside of my windows will fog up from my breath. With more people in the car this is even more exacerbated.

Any idling will waste gas, but I find a 4-6minute warm up just perfect to have defogged windows & heat starting within a few blocks. My usual weekly summertime average is 34mpg, with idling & winter temps that has dropped to 29mpg. I'll spend the extra $6 a tank to be comfortable & be able to safely see to drive.
 

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Discussion Starter · #9 ·
Number 3 kinda contradicts 4. If I were to drive my car it would take 5 minutes to generate any form of heat, which means the inside of my windows will fog up from my breath. With more people in the car this is even more exacerbated.

Any idling will waste gas, but I find a 4-6minute warm up just perfect to have defogged windows & heat starting within a few blocks. My usual weekly summertime average is 34mpg, with idling & winter temps that has dropped to 29mpg. I'll spend the extra $6 a tank to be comfortable & be able to safely see to drive.
You are correct that 3 & 4 will sometimes conflict. Sometimes the best solutions will conflict and you need to figure out your best compromise between them. Personally, I never start my car before I'm clearing off snow and ice unless the ice is really thick. In that case I'll start the car and use the defroster to start warming the windshield while I clear the other windows.
 

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Discussion Starter · #10 ·
Now that's warmed up some here in Denver I can safely say that bitter cold really kills the MPG in the Cruze. I normally see 47+ average MPG on my DIC if I'm only driving my normal commute. During the cold snap a couple of weeks ago the best I could do was 43 average MPG. I think this was due to increased rolling resistance and my tire pressures fluctuated from 37-38 cold to 42 warm during my morning commutes. Without putting air in the tires they are back up to 42 cold to 45 warm now that the outside temps have risen.
 

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Air density is the big killer at those temps. Friction is a B****
 

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Discussion Starter · #12 ·
Hadn't thought of the increased air density. You're right, it will definitely add to the velocity induced drag on the car.
 

· Epic Beard Man
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Hadn't thought of the increased air density. You're right, it will definitely add to the velocity induced drag on the car.
I was thinking about this the other day. I wonder what effect the increased air density has on the turbo, because I can hear it now more than ever. Which, my fuel economy is certainly suffering both from the cold and my new found love. I never used to get much turbo sound with a stock intake and K&N panel.
 

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Discussion Starter · #14 ·
I don't know how much of the additional drag is rolling resistance vs. air drag, but I do know there is a hill I drive down at 6:10 - 6:15 every morning. When it's cold outside I get about 50 yards less coast in or out of gear before I have to downshift from 6 to 5 to go up the next hill. Since the distance difference is constant regardless of clutch in or out this tells me that it's not increased internal engine friction but increased rolling and air drag.
 

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I was thinking about this the other day. I wonder what effect the increased air density has on the turbo, because I can hear it now more than ever. Which, my fuel economy is certainly suffering both from the cold and my new found love. I never used to get much turbo sound with a stock intake and K&N panel.
Turbo + cold air = amazingness.


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I was thinking about this the other day. I wonder what effect the increased air density has on the turbo, because I can hear it now more than ever. Which, my fuel economy is certainly suffering both from the cold and my new found love. I never used to get much turbo sound with a stock intake and K&N panel.
Denser colder = More oxygen in the air charge which = more HP and less gas mileage.
 

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2010 1.4 turbo cruze.
Have the same problem with gas milage. In toronto canada the tempeure has been 10 to 18 degrees below frezing for over a week. My gas milage has droped so much i have to wonder why. On city driving a normal with tempeture just on freezing would be 8 liters per 100 miles. In this weather it is runing any where from
14 to 16 liters 100 miles. That seems allfull high to me.
 

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Cold drag is endless,
All 4 wheel bearings resist movement, four tires resist flexing, internal engine drag increases, alternator drag increases due to high current needs (ie, a battery resistant to charge, lights on, frequent wiper use, its own cold bearing drag)
Fuel enrichment for cold start and engine drag, trans oil that doesn't want to flow as well as every bearing in it.
And, yes, drag induced by dense, cold air.
If used, snow tires have very high rolling resistance as well.

Quite a conspirancy against fuel economy if you really grind on it.....I'm surprised they do as well as they do.

Rob
 

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Had an interesting time over the weekend with 4 people in my car including myself. Temperatures were 20-25 degrees F, and I couldn't keep the car from fogging up. The best setting that actually de-fogged all of the windows including the rear was to set the car to defroster mode with the recirculate function on. I believe this causes the A/C compressor to run for defroster function, which gradually keeps removing moisture from the air inside the car.
I haven't tried it in the Cruze to see if it works or not, but most cars I've driven with electronic environmental controls will lock out the recirculation if you have selected defrost. Maybe the Cruze is different?
 
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