My gas mileage has decreased

Old Man Winter?

 

I'm the first one to say check the vent of the battery compartment in the back seat driver's side to make sure nothing is blocking the air flow.

 

i'm with etc, is it snowing yet? spring is just around the corner!

 

if it's not the vent or the cold, i would fill out cwerdna's sticky questionaire about mileage problems.

 

Here is the fuel economy questionnaire:
Fuel economy complaints/queries? Please copy, paste & answer these questions, esp. if you're new

See also:
Why mileage gets worse in winter

Here is a graph showing typical seasonal MPG variation, in this case the first two years of my 2010 Liftback:

 

Check the vent in the drivers side back seat floor board. Sounds like something is blocking it.

Edit: Sorry, didn't realize this has been suggested yet. I'd be surprised if this wasn't the cause.

 

It's cold in Minneapolis, isn't it?
We've had essentially unrelenting sub-freezing temps. since late October. Plus it's night and my windows fog up. As a result, most of my trips (if under 5 miles) are now 30-50 mpg, compared to 40-70 mpg in the summer.
Brrrr...I want some hot coco

 

I noticed a difference in gas mileage on my Prius c just from driving 25 miles on Sunday mornings to the golf course and then driving home 5 hours later. The only thing I could attribute this to was the cooler temperature in the morning as opposed to the afternoon return trip. I would get 57 to 60 miles per gallon in the morning and would get 65 to 67 in the afternoon, one time getting 70 miles per gallon. Now I struggle to get to the low 50s mpg as the temperature in upstate New York has turned cold.

 

Winter blend fuel?

 

Alright here's kind of a dorky question: What's the best/fastest way to de-fog the windows when I get in my car at night and it's cold? Defroster takes forever to do anything and I'd rather just get on the road than wait 5 minutes but the glare is terrible.

 

Do everything suggested above! And then...

Tire pressure can drop 1 psi per 10 degrees of temperature drop. Often, when we get our cars serviced at Toyota, the service department will set tires at 35 psi in the warm 65-70 degree heated shop, and then we drive out into 35 degree air (or colder as we get deeper into Winter). Within a fairly short time, you may be riding around on 30 to 32 psi tires. Check those tires with a gauge. Make sure that in the cold of the morning, you're at least at 35 psi. I run my Prius at 40 front and 38 rear. I check my tires every couple of weeks and adjust as needed.

How much "stuff" do you carry in the back of the car? The more stuff you have in there, the more weight, so the more fuel you have to use to lug it around. The lighter the car, the better the mpg.

It's getting colder outside. How much heat do you demand? Do you have the windshield defroster on? Is your windshield fogging up, so you run the defrost at full tilt to keep it from fogging? If your windows are fogging up in the Winter, clean them with a quality car glass cleaner. The plastics out gassing inside the car and pollution in the air will eventually coat the inside glass with a film that will help cause fogging.

Make sure that you also open the outside air vents in the heating venting and air conditioning system. Using recirculated air in the Winter at first will help heat the cabin, but will eventually lead to increased cabin humidity that can cause cold interior window surfaces to fog up, even if they are all squeaky clean! Like in Summer when you put ice in a glass, and it causes the glass to moisten up as the dew point is reached, same thing happens to a car, only the ice (Winter) is outside and the glass moistens inside.

Dress for Winter. Hat, gloves, coat. That way you won't have to run the heat as much or as hot, and you'll help the engine run under less load, helping out mpg. You don't have to suffer, but being somewhat reasonable will allow more efficient engine operation. I know people that wear summer weight clothing during the cold months, pre-heat their cars in the driveway for 10 to 20 minutes to warm the interior to tropical levels and then complain that their mpg is horrible. I believe them!

Your car only has a little over 5,000 miles on the odometer. It's not even fully broken in. It will get better mpg after around 10,000 miles or so. Also make sure that your dealership is using the Toyota recommended synthetic 0w-20 oil.

And finally, (whew!) a 12.5 mile commute to work is just barely enough time for the engine to hit full operating temperature... so, keeping the accessory use to a minimum will help get your engine up to temperature. Ease out of the driveway and take it easy until the engine builds up a little heat.

When I lived in Montana, I kept my car in the garage. When it was really cold, I had a blanket over the hood and a 100 watt light set up against the oil pan. Even in mornings when the temperatures dipped well below zero, I had no problem starting the car, and it warmed up right away. Only used the lamp a few times on some of the colder Winters. I have not used that here in Maine, since it doesn't get quite as cold.

By the way, you have the exact same commute distance that I have! Hope any of this helps out. Unfortunately, like the certainty of death and taxes, Winter temperatures and Winter fuel blends will drop everyone's mpg.

 

Yup. No surprise either.

This morning's commute was at 25°F.

The usual MPG drop from the approach of winter quite apparent.

Good times.

You won't be able to overcome every factor that comes along with the dropping temperature, but at least you'll know efficiency is still better than with other vehicles.

 

Rain-x makes an anti-fog thing to wipe on the insides of your windows. It's some form of alcohol. Here's someone suggesting vinegar and water: How to Make Anti Fog Solution? - Ask.com I've also heard of rubbing plain shaving cream on it.

 

25 degrees... approach of winter... oh dear... you can keep that crap.

 

Hah that's nothing, we get that for 6 months...try -25 degrees

 

... why do you people live there?

 

I can visit if that's all the north is good for. ... But I certainly wouldn't want to live there...