Steam loco be more fuel efficent in the summer than winter?

A steam loco needs to boil water to make steam, would a hot summer day make be more efficent? If temp. is 90 as opposed to 10 wouldnt it take alot less fuel to produce steam?

IIRC, the efficiency of a steam locomotive is determined by the difference between the internal steam temperature and the exhaust temperature. So it should be more efficient in a cold environment, no?

No reason cold weather would make the engine more efficient. If the exhaust were colder, that would just mean more of its heat had been absorbed by the cylinder walls, or something-- that heat wouldn't have done any work.

As to Trainman101's question, I think the answer is that, in principle, warmer surrounding air (and-- assuming that the water in the tender is in thermal equilibrium with the atmosphere-- warmer feedwater going into the boiler) would lead to fuel economies, but I don't have a quantitative estimate of how much it would do. I ***think*** railroads in the norther U.S.A. noticed the difference between summer and winterr efficiency, but I'm not sure where I got that idea.
Certainly radiative heat loss (well, initially, conductive heat loss from boiler water and steam to the metal around it and then radiative loss to the outside air) was a problem. The main advantage of compound locomotives (which were more efficient in operation, though most U.S. railroads decided their additional mainenance costs outweighed the efficiency) was, I think, that they reduced this loss: since the steam only expanded partially in each cylinder, the difference between beginning-of-power-stroke and end-of-power-stroke temperature in the cylinder was less than in a "simple" locomotive, so heat-loss to cylinder walls was reduced.
French railroads were much more concerned than American with thermal efficiency of their steam locomotive. (The U.S. has better supplies of cheap, good quality, coal, so could afford to be wasteful.) Under the direction of André Chapelon, the great 20th century steam locomotive designer, one French railroad (possibly the unified national SNCF, possibly one of its private predecessors) did controlled experiments to see which features did the most to improve efficiency: one of the best was putting steam jackets over the pipes between the boiler and the cylinders (& maybe-- I don't remember-- the cylinders themselves) to keep the metal the steam came in contact with hot. Running the locomotive in hot weather would have a bit of the same effect, but again I can't tell you anything quantitative.

Industrial and large commercial stationary boilers will frequently pre-heat the air supplied for combustion in order to improve efficiency during the winter months.

Well, the efficiency of the whole locomotive is only minor influenced by the climatic environment temperature.
Sure: In summer the loco comes up much better to pressure, but this is more, because of the feeling, as of realy time. In cold winters outside, you do not allways tend often and well for the fire, you usually go more often in the shed to warm yourself up... in Summer, you nearly sit on the cab, watching the things going on...

Usually to most thing to make a steam engine more efficient is to reduce the loss of unburned fuel.
Next comes the waste of thermal heat be improper boiler and combustion aera designs, like the smokebox gas losses and improper superheater designs...
If you can erase those losses, you have a boiler with more than 80% efficiency... the rest of the efficiency work, for the boiler is a air controll and automation for combustion air supply, and with all those things you can create a boiler with over 95% efficiency.
The steam engine itself need a cmplete redesign to make if more efficient. Different steam supply, different valve and piston designs, different lubrication.
If you can, simply go and attach the steam engine to a hydro gear box and make it switchable...
There are so many things.... so summer and winter would realy not count.

All stationary steam boilers have a combustion air preheater, usually only large boilers have such a thing big enough to realize.

We all know that heated air is lighter than cold air. Hot air balloons depend on this. Similarly, the warmer the outside temperature, the more efficient a steam locomotive would become. The outside air would effectively be a huge heat sink. So, the colder the outside air is, the more fuel would be needed to raise the temperature to boil the feedwater and produce the steam. Those conversant in the area of Thermodynamics should weigh in on this one.

Pennsy,
sure... But: How much will it have effect?
We talk not about a delta T of some 100° Kelvin, we talk about often only less than 20° Kelvin at all.
So if you will measure a large effect, you hae to ensure a capacity of raining the air temp for combustion so over 390° F, and now we are talking about a overall delta T of over 200° Kelvin in winter and over 160° Kelvin in summer... That's the point.
So the climatic influenced temperature will not significantly influence the overall efficientcy of a steam locomotive, as other factors do.
This little effect is realy something you can forget about thinking.
Consider, that to all fuel feed to the locomotive only less than 1% is realy need for heating up air mass, while over 50% of fuel goes unburnt away...
And only less than 1% is radiation loss, exaample radiation loss from the boiler outside surfaces to atmosphere...
Also: Serious efficiency loss comes with the way of driving: If I blast my steam with 220 psi throught the chimney and have a boiler pressure of 294 psi, I waste so much energy, that the cold winter air won't have any effect on overall efficiency...

So I am sure: There are enough drivers, wo will make the engine only by different driving more efficenct than the measureable differences betwen summer and winter.

So forget that summer and winter efficiency thing. It won't realy count... and if: That two or three shovels of coal you may save in summer will often be blown right trought the chimney by bad stoking techniques (a firemans failure) or a bad driving style... The one by smoking around like hell, the other one by not realy use the steam as is should be done...
So, if you spare those three shovels in summer, I know how to spare much more, even in winter, by good firing and driving skills...

So what's more efficient?