Longer warm up time due to cold temps....runs richer.....

 

^^ This plus "winter blend" crap gas which always nets less mpg.

 

check the simple stuff first, tire pressure, binding brakes, dirty air filter

 

Check switching times on both upstream 02 sensors.

 

On the F150 forums, it was mentioned that during winter months, gas stations switch to some sort of a different fuel blend that yields the lower mpgs. It was brought up because a lot of us ecoboost owners were like, "wtf?", when we went from 17-19 combined to 14-15 across the board.

EDIT: Sousa beat me to it.

 

+1 To all of the above. Depending on what kind of driving you do, 19.8 isn't terrible for the car. I'm usually at the high end of the charts (tanks at 27-31mpg) in summer, this winter I'm barely making 24mpg.

 

Beside what's listed above, the thing people always seem to forget about cold weather is its effect on aerodynamics. While denser cold air is good for HP and engine efficiency, that thicker air requires a lot more energy to push a car though at 70 MPH.

Depending on the car, the sweet spot for economy is usually between 60 and 80 degrees. Below that, the thick air starts to kill your aerodynamics. Above that, the thinner air hurts engine efficiency. With modern fuel-injected engines though, the penalty for hot intake air is usually much less than damage cold air does to your aerodynamics.

 

All of the above PLUS something from my personal experience:
A few months ago I had to change the fuel pump. For a week or so before changing it, I checked the fuel pressure most of the times it was around 34-35 PSI; after changing it - 39-40 PSI. That was around the time they switched gasoline types. Even with the worse gasoline, the straight highway, constant 70MPH cruise control ON MPG went from 25-27 to 28-30.

Maybe the higher pressure lead to better fuel atomization?
Also, at about the same time I used some Techron fuel injector cleaner

I hope this helps!

 

You lose 1psi in tires for each 10f temp drop. You can be significantly down in psi from the height of summer to the depths of winter.

Your cold fill pressure needs to stay constant year round.

 

+1 to all of the above, plus in the very cold weather it takes the torque converter much longer to lock up, turning some engine power, and therefore fuel, into heat in the transmission. The First Law of Thermodynamics strikes again.

 

About that, the torque converter locking temperature is dependent both on outside as well as starting coolant temperature. The trick being to turn off the engine and on again when the temp needle passes the first line (which is at about 57C or 135F).

 

Remember that cold weather is NOT your friend when it comes to mpg.

 

Thanks to all respondents, very good information provided, i am a wiser man today !!!!!!
I never would have thought that cold/hot temps would significantly affect the fuel consumption etc

So need i not worry that possibly there is a problem with the coil ????

 

This response will be most helpful to folks who keep their Taurus's long enough to be driven, or towed, to the wrecking yard:

You didn't specify mileage. I had a Taurus that gave me 25mpg consistently. Suddenly (and this was in the summer), mileage dropped to 18mpg. The car had 140,000 miles on it. Considering it was running great, and tire pressure was just fine, I took the car to work, all highway driving, and got out and checked the temperature of the front wheel hubs with my finger. Left side hot, but not to hot to keep my finger on it. Right side...OWCH!

Replaced the front wheel bearings and mileage went back up to 25mpg.

 

Good point. Bad wheel bearings or dragging brakes, often due to seized caliper pins, will kill MPG.

 

^+1.