Do jet planes (757, for example) use more or less fuel in cold weather?

I have no certain knowledge, but I’ll offer a hypothesis:

I would expect that the plane’s fuel consumption at takeoff and landing (can’t forget that landing also requires fuel) in cold weather – controlling for all other factors, including wind speed and direction, humidity and precipitation, runway surface condition, etc. – would be lower than it is in warmer weather.

Cold air is more dense than warm, so it seems to me that the plane’s wing surfaces would be more efficient then, leading to lower consumption.

Nothing definitive (I am not a pilot) but my logic based on a smattering of knolwedge:

The “three H” rule defines what makes take off difficult: High (altitude) Hot, and Humid.

In cold air, the plane has more lift with less pwoer. so I will posit that cold air requires less fuel on take off.

One of my good friends is a pilot. I asked her and here is her answer: the colder the air the more dense the air, therefore less fuel overall. The wing on the plane is more efficient in producing lift. I believe engine combustion is also more efficient.
However, I believe the jet stream moves south in the winter so half the time you get very strong headwinds. So it adds more time in the air, therefore more fuel is used.

In cold weather the air is denser so more air enters the engine making the engine more efficient. This also means that more fuel is required.
Also as the air is denser aerodynamics suffer as the denser air gives more resistance.

Ok, now I am thoroughly confused.

@chyna‘s friend says “less fuel overall” (but then there’s the jetstream issue if you’re flying the wrong direction)

@Lightlyseared says “more fuel is required”

@CWOTUS and @zenvelo both come down on the ‘less fuel’ side.

Hmmm.

@elbanditoroso I think @chyna said it best. The Jetstream isn’t really a factor in the question. Let’s say the plane flew 500 miles North with the Jetstream and then back against the Jetstream. The overall fuel consumption is the average of the two.
How dense the air is at flying altitude is negligible at best since the plane could fly higher into air that was always the same density for whatever test we’re doing to find the answer to your question. And the air is always very cold at extreme altitudes. But flying up to cruising altitude and returning to low altitude for landing might produce better fuel economy.
I did a test years ago with a car to determine what would give me better fuel economy: Keeping the engine at a high RPM whenever possible vs. keeping the engine at a low RPM and always under the exact same conditions. The MPG was almost exactly the same. So what would matter more than anything else was the actual amount of work being done by the engine.
So my answer to your question would be, you would get slightly better fuel economy on the plane when taking off and climbing to altitude, and while getting more power from the engines and the cold air producing more lift, the plane also has to move through that heavy cold air, pushing it out of the way. Otherwise, no difference to note.

I agree with @Lightlyseared. Engines produce more power in cold air but fuel consumption increases along with power. Scientifically, air contracts when it is cold and denser. This means that the air your plane is taking in during combustion has more oxygen in it. When there’s more oxygen, the engine compensates by using more fuel. Source

@flutherother I have to disagree with that last part, If there was more oxygen to make the engine use more fuel it would produce more power so a lower throttle setting could be used. This is true of automobile engines at ground level as well as aircraft at high altitudes. Air/fuel ratio remains the same.

The pilot can control the thrust but as the engine efficiency is better in low temperatures there should be some fuel saving.

Since the air thins more and more as the plane rises to cruise altitude, constant adjustments would have to be made to provide the correct the air/fuel ratio, otherwise unburned fuel would be pouring out of the rear of the engines at anything above the altitude they were set to run, or run excessively lean at altitudes below what they were set to run. If engine efficiency is better at low temperatures, it would also be true at low altitudes, regardless of ambient temperature. And planes do most of their flying at high altitudes where the air is cold and thin, a constant.
I think your question, @elbanditoroso , is entirely moot. Maybe you can find the answer to your question this way: Drive your car like you always do, and carefully check the mileage in both summer and winter, (possibly for 5 years, say,) then compare the results. Be sure to keep the tires properly inflated at all times, and don’t let the engine warm up for more than 2–3 minutes in the winter. Or, if you take a long day trip in the winter when your car can be fully warmed all the time, and the same trip in the summer. Maybe more than once. Compare results.

Cars are less efficient in the cold.

https://www.fueleconomy.gov/feg/coldweather.shtml

That’s why the car would have to be adequately warmed up. Not just the engine but the gear train and tires, too. Hence the long trip I mentioned.