Lower MPG in the cold....

[GreenTea2008]

The gas mileage on my wife 2008 CR-V AWD has dropped considerably in the past couple weeks. We bought the car in the Summer. At first, it averaged around 25 MPG. Now, it's averaging only 21 MPG. Her commute to work is 18 mile each way (Hwy and suburban road). Initially, I thought the trip computer might be at fault. So, I calculated the MPG by hand after a fill-up at the gas station. I got the same result! The only other thing I can think of is the weather. It has been round mid-30s here this month. I asked her to warm up the car for a minute or two before driving. It didn't help. A friend of mine who lives close by has the same CR-V and he is having the same problem. Is there anything else we could do?

[sleeksilver]

Stations have switched to the winter blend of gas which will decrease your mileage.

Nothing you can do, it happens to everyone.

[Jwood70]

Stations have switched to the winter blend of gas which will decrease your mileage.

Nothing you can do, it happens to everyone.

x2. try using a higher grade gas. that will help some

[sleeksilver]

x2. try using a higher grade gas. that will help some

It shouldn't, and if it did it would not offset the higher cost...

[GTCB-chris]

what exactly do they change between the summer/winter blends of gas?

[Jwood70]

It shouldn't, and if it did it would not offset the higher cost...


Why wouldn't it work? (I'm not arguing cost)

[Badgerland]

Why wouldn't it work? (I'm not arguing cost)

Higher octane doesn't equate to better gas mileage.

[sollybro]

Those of us living in northern climes have already started to notice the seasonal decline in fuel economy, even with careful attention to sagging tire pressure (probably the best known effect of the mercury's slide).

Yet, despite diligent all-around maintenance and continued careful driving, cold weather fuel consumption can be dramatically worse than in warm temperatures.

How much worse?

Have a gander at these calculations for a Honda Civic hybrid at 60 MPH in varying ambient temperatures:

MPH-----AMBIENT-TEMP-----MPG (US)

60------------95----------52.98
60------------85----------52.62
60------------75----------51.16
60------------65----------49.12
60------------55----------47.22
60------------45----------44.67
60------------35----------43.05
60------------25----------41.54
60------------15----------39.41
60------------05----------38.09

Look at the extremes: the coldest MPG is 28% lower than the warmest.


Why so bad? Off the top of my head, I could think of a couple of reasons to explain it, but together they didn't seem significant enough to account for the magnitude of the change. With this mystery to solve, I hit Google. And here's what I learned...

9 reasons your winter fuel economy bites

1. More idling

This should be a no-brainer, yet parked idling cars are a common sight in cold weather. Resist the temptation to idle your car to warm it up. An idling engine gets 0 mpg. Consider also that idling the engine does nothing to warm up the tires and drivetrain.

Even in the coldest weather, you can begin driving after 30 seconds from a cold start - keep speeds low/moderate and use gentle acceleration until the temperature gauge starts to climb (source).

2. Low tire pressure

Of course you're smart enough to keep up your tire pressure as the temperature drops, right? A 10-degree (F) change in ambient temperature equates to a 1 psi change in tire pressure (source). Fuel economy declines 0.4 percent for every 1 psi drop (source).

3. Increased rolling resistance

Even if you're completely attentive to proper tire pressure, cold ambient temperatures will still cause your tires to return worse mileage. That's because a tire's shape isn't completely round - the sidewall bulges out at the bottom, and where the tread meets the road the small contact patch is actually flat. As the tire rotates, it constantly deforms to this shape, and this deformation requires more energy when the rubber is cold and hard. Rolling resistance at 0 degrees F is 20% greater than at 80 degrees (source 1, source 2).

4. Crappy road conditions

It's increased rolling resistance of another kind: driving through slush and snow. And then there's its wasteful polar (no pun intended) opposite: no friction at all! (A.K.A. wheelspin on ice.)

5. Lower average engine temperature

In the winter, an engine takes longer to reach operating temperature and cools off faster when shut off. Since the engine management system orders up a richer mixture when cold (proportionately more fuel in the air/fuel combination), more fuel is being burned overall.

A block heater can offset this problem (improving fuel economy by 10% in sub-zero conditions - source), as can garage parking, and combining trips (to minimize the number of cold/hot cycles).

Also related...

6. Higher average lubricant viscosity

Engine oil thickens as it cools. So does transmission and differential fluids and even bearing grease. Significantly more energy is needed to overcome the added drag these cold lubricants cause.

Using synthetic fluids can address this problem, since their viscosity changes less at extreme temperatures than traditional mineral fluids.

7. Weaker gasoline

Gasoline doesn't vaporize readily at very cold temperatures. So oil companies formulate fuel differently for cold-weather markets in the winter. Unfortunately, the changes that provide better cold vaporization characteristics also result in less available energy for combustion. You won't get as far on a liter of winter gas as you will on a liter of summer gas. (Source.)

8. Higher electrical loads
In colder temps, you use electrical accessories more often:

- lights (in higher lattitudes it's darker in the winter)
- rear window defroster (because it's easier than using the ice scraper, right?)
- heater blower motor (I don't have a/c, so this isn't balanced out during warm conditions); heated seats/mirrors
- windshield washer pump (because it's easier than using the ice scraper, right? And for frequently cleaning off dirty road spray.)

9. More aerodynamic drag

No, I'm not referring to the layer of snow you're too lazy to brush off the top of the car (though that would hurt mpg too).

A vehicle's aerodynamic drag is proportional to air density, and the density increases as temperature drops. For every 10 degree F drop in temperature, aerodynamic drag increases by 2% .

[Jwood70]

Higher octane doesn't equate to better gas mileage.

no, higher octane= cleaner burning, which means less un-burnt gas escapes with the exhaust.

[sollybro]

no, higher octane= cleaner burning, which means less un-burnt gas escapes with the exhaust.

That isnt entirely correct.

Here is a great article about what the term octane refers to in chemistry, and how this 'octane rating' in fuel affects the engine controls:

http://en.wikipedia.org/wiki/Octane_rating

[Badgerland]

Sollybro, your post #8 was right on target...I was just too lazy to type all that! :D

[Jwood70]

I stand corrected. Thanks for the information.

[SniperD]

Glad to see this post. I thought something was wrong with my CR-V.

[JeffsFirstCRV]

Glad to see this post. I thought something was wrong with my CR-V.
Me too. I bought mine in August and it has about 3000 miles on it. During the first 500 miles or so, I was getting about 23 MPG in the city. I was expecting improvement after the break-in. Instead, it started going down. Now I'm getting between 20 and 21. I live in Western PA, where not only do we have to contend with some cold temperatures, but not so pleasant road conditions - as well as a constant array of hills.

[Badgerland]

Me too. I bought mine in August and it has about 3000 miles on it. During the first 500 miles or so, I was getting about 23 MPG in the city. I was expecting improvement after the break-in. Instead, it started going down. Now I'm getting between 20 and 21. I live in Western PA, where not only do we have to contend with some cold temperatures, but not so pleasant road conditions - as well as a constant array of hills.

I think yours is a very common thought on owners. People fail to realize that the "new" EPA gas estimates are 19 city and 26 hwy for the AWD version of the CRV; combined is 22. As the weather turns cold it is very common to drop 2-4mpg as the winter blend gas and colder temps make things worse.

For more info on real world EPA estimates a good link is http://www.fueleconomy.gov/feg/findacar.htm

Have a great day.

[Bren08CRV]

Yeah I definitely notice a difference! I'm glad I'm not the only one!!

[rslayback]

One thing you may want to add to the causes, is during the colder months the defroster is used which uses the AC compresser. This is done to help in clearing the windshield faster. Any of the heat modes that use the defroster will engage the AC compresser.

[gary696]

One thing you may want to add to the causes, is during the colder months the defroster is used which uses the AC compresser. This is done to help in clearing the windshield faster. Any of the heat modes that use the defroster will engage the AC compresser.

But the AC is probably used alot more in the summer.

[kaapso]

Those of us living in northern climes have already started to notice the seasonal decline in fuel economy, even with careful attention to sagging tire pressure (probably the best known effect of the mercury's slide).

Yet, despite diligent all-around maintenance and continued careful driving, cold weather fuel consumption can be dramatically worse than in warm temperatures.

How much worse?.................
........
9. More aerodynamic drag[/B]

No, I'm not referring to the layer of snow you're too lazy to brush off the top of the car (though that would hurt mpg too).

A vehicle's aerodynamic drag is proportional to air density, and the density increases as temperature drops. For every 10 degree F drop in temperature, aerodynamic drag increases by 2% .

Well said.

[motoguy128]

One thing you may want to add to the causes, is during the colder months the defroster is used which uses the AC compresser. This is done to help in clearing the windshield faster. Any of the heat modes that use the defroster will engage the AC compresser.

Yes, but at winter tempertures, the power consumed by the compressor may be as much as 1/2 that on a hot summer day and it will cycle on less frequently.

A cold engine will consume a certain amout of fuel just warming the engine block, oil, and coolant. Also, an engine cannot run in the most efficient lean fuel mixture until it's fully warmed up.

[fujisawa]

I'm pretty impressed with Solly's post, to be honest.

I've noticed a huge decrease in mileage since moving up to rural NH, where bizarrely the local traffic is actually worse than Boston. anyway, that's a huge part of it, since it's all stop-start traffic, but I bet that they switched to winter gas recently as well (it snowed last Monday for the first time).

don't forget the increased oil resistance as well. i bet that's something.

although it's not really relevant here, although idling your car gets 0mpg for every minute you run it ... it's sure a lot nicer than driving off in a car which blows cold air at you. what for we have jobs to pay gas bills if not to have some modicum of comfort in cold winter months?!

last - at least on the 02-06 - you can turn off the default defrost-mode AC, allowing you to run the defroster without the AC unit turning. now, to be honest, you normally will WANT the AC unit on (the ability to turn it off is mostly helpful in spring/fall), but i just thought I'd mention it. turning if off just requires some button-pushing, no modifications required.

[motoguy128]

no, higher octane= cleaner burning, which means less un-burnt gas escapes with the exhaust.


The opposite is more liekly the case. IF an engine is not tuned for higher octane fuel, it's more conservative ignition timing may cause more unburnt fuel. Althouh with todays lean mextures, EGR, and O2 sensors, using any grade fuel is liekly to give you the same results in terms of mileage and emissions.

Ultimately the difference between 87 octane and 92 octane is not night and day. We're not talking about 105 or 110 octane race fuel or Aviation fuel.

With higher performance engines, the higher octane with their particular tuning will allow the engine to make a little more power. Most of these engines will run fine on lower octane fuel, but make less peak power. These engines/cars will likely get similar mileage with either grade.

[motoguy128]

As for idling... Looking at my calculation for my mileage on days when I have not been letting my car idle compared to days when I have been, I see a 2 mpg drop from 13mpg to 11mpg. Using a best guess of my average speed I figure that while idling, the car consumes about 0.4 gallons per hour. SO at $2.50/gallon, it will cost you about $0.08 to let a car idle to 5 miuntes.

That's really, really cheap for a little extra confort. If you let it idle 60 days per year on the coldest days, it will cost you around $5 for the winter season.

I'll guarantee that a engine block heater will use more than $5 in electricity. $5 in my area will get you 38 kw-hr. If you have a 300watt block heater, you would only need to run it 126 hours to cost you $5. Over the same 60 days, that's a little over 2 hours each night.

Ye,s there's some engine wear with idling, but on a modern engine the limiting factor on the engien or the vehciles overall life, will not be an extra 300 minutes of idling each year. Most enignes fail for reason other than internal engine wear... and most cars ar escrapped because of rust, of costly repairs ot other compoentns such as transmissions, electrical systems, etc.

[beany2510]

Hi, so I've had my 2.0petrol SE MT roughly 2 weeks, and was alarmed in the first instance as to how swiftly the gauge drops. I have just filled the tank back to the top and done my first mpg calc.
i have a 4 mile commute (each way) in city traffic, the weather here in the England has been pretty shocking for most of the last few weeks average temp last week was probably -1degC with plenty of snow and ice, its been better this week so far.
MPG worked out at 26. I'm not not so worried about the fuel economy, if i can get this in cold winter weather in a 4 mile city commute, then the warmer weather shouldnt be so bad.
oh and it was using regular unleaded at a Shell station (cost /gallon £4.94, or $8.04/uk gallon).

[belgarion_v]

Yes, but at winter tempertures, the power consumed by the compressor may be as much as 1/2 that on a hot summer day and it will cycle on less frequently.

My last car was a Saab and the manual said that the compressor would run when you set the car to demist the windscreen (windshield) as this makes it clear quicker, and it does because I've tried it. I've noticed that my Honda appears to behave the same.

Hi, so I've had my 2.0petrol SE MT roughly 2 weeks, and was alarmed in the first instance as to how swiftly the gauge drops. I have just filled the tank back to the top and done my first mpg calc.
i have a 4 mile commute (each way) in city traffic, the weather here in the England has been pretty shocking for most of the last few weeks average temp last week was probably -1degC with plenty of snow and ice, its been better this week so far.
MPG worked out at 26. I'm not not so worried about the fuel economy, if i can get this in cold winter weather in a 4 mile city commute, then the warmer weather shouldnt be so bad.
oh and it was using regular unleaded at a Shell station (cost /gallon £4.94, or $8.04/uk gallon).

My diesel CRV almost got as low as 35mpg the other week, but that was during the worst of the recent cold weather. And as for for 4 mile commute, some days I had travelled 4 miles before the temperature guage began to register. Mpg climbing back towards 40 again now :)

Vince

[CRVguyEX08]

I too noticed a big drop-off in the mileage for my 2008 CRV EX in the winter. After some research, I decided to switch to a premium synthetic oil that was still approved (API certified) for use in my vehicle that is still under warranty. So far, I am impressed with the results. I made a video to document some of my initial impressions. As CRV owners, I thought this video might interest you before your next oil change.

Here's the link:
http://www.youtube.com/watch?v=yGMrka3daUI