Yes, ther certainly seems to be a relationship between FE and temp. An engineer friend is wondering if perhaps preheating intake air might improve things. My thought was to tap off the radiator, run hot coolant through a coil of copper tube (or motorcycle oil cooler) in the preexisting or modified air intake. The Ford Escape Hybrid does have a temperature sensor that fires up the engine to keep it warm and in cooler climes where the engine block would cool more quickly. I am not certaing which is more important, air temp in the intake or cold weather chilling the engine block.

 

There is another approach some of the Prius folks have been investigating:



This works by letting the ICE autoshutdown even before it reaches 70C. This stretches out the warm-up and avoids running the ICE just for warm-up. For the technical details:
http://hiwaay.net/~bzwilson/prius/pri_temp.html

Bob Wilson

 

I admit to being confused by these results, but some have brought up other factors, such as the winter fuel mix, wind, snow or rain to plow through, etc. But it seems to me that if ALL other conditions EXCEPT for the temperature are the same, that an engine should get BETTER mpg in COLD AIR, since it is DENSER. Small airplanes sure perform better in cold air, as hot air makes for a higher "density altitude", resulting in poorer engine performance and less lift for the wings (this from a 30 year pilot)

 

After the engine is warmed up, cold air is fine although a little denser. Since lift is a function of air density, the lift improves significantly along with the higher engine output. However, in a car, lift is static, from the tires, so drag is a little higher. But these are minor effects compared with the task of keeping the ICE coolant above 70C.

The real problem is the control computers are trying to keep the ICE above 70C. The ICE is in a compartment meant to cool it. Even with a radiator block, significant heat loss occurs in cold weather. Meanwhile, the heater is also trying to keep the cabin warm by tapping the coolant, further cooling the vehicle. So the problem is in cold weather, the ICE will sometimes be run just to keep the coolant above 70C, actually 60C is the lower limit once 70C has been reached.

What is nuts is the exhaust pipe is still throwing away 1/3d of the heat energy. The problem is finding a working fluid or system that can handle the temperature ranges.

Bob Wilson

 

Performance in terms of power does come with denser air, but that's only because of more fuel, the mpg won't go up with more fuel.

 

I do use many "hypermiler" tips and tricks to get up to 53 MPG tanks in a 4,000 pound SUV... but many people contribute my fantastic results to the thinner ( less dense ) air of Colorado.

When there is less oxygen per cubic ft, it requires less fuel per cubic foot.
At the cost of horsepower, right? But WHO CARES! It takes 20 horsepower off the top end, not the bottom end... and does not effect the electrics at all. So my max. output is maybe 135HP vs. the 155HP possible at sea level.

Now, how often is everyone at max. power output? Rare to never.
I never miss the loss of a few HP at the top end, but I enjoy increased fuel economy every day, year-round.
-John

P.S. You actually want WARM air intake, not cold. Only gasoline vapors burn. Liquid gasoline will not burn, and will go right out the exhaust.
At cold temperatures, the gasoline will atomize ( go into a fine liquid mist ) but not vaporize ( go into an invisible gas that burns ). You will waste more gas, and cause more pollution with cold air vs. warm.

 

Of course Temperature plays some important role for car fuel economy. It effect all parts of our car like bearings, joints, transmission, power assisted brakes.