Hot air intake?
 

As the cold (relative, since I'm in central TX, cold is anything below 60 degrees) temps here in Austin I've been noticing how much the cold air effects my MPG on my '08 LS 2.2L manual.
For instance:
On my way to work in the afternoons the ambient temps are ranging from 65-75 degrees
and I average around 33-36 on the highway (Most of my commute is highway) at 60-70mph.
However on the way back home, around 10pm, it's much colder ambient temps...usually around 40 degrees.
I can barely average 30 mpg on the way home going 60mph.
I realize my tire psi's are slightly lower in the colder temps, but they're not much.
In the heat, the tires are at 35-37psi...in the cold they're at about 32-35. I hypermile as much as possible.
I realize this is still normal for the HHR, but I can' just leave something alone if there's a possibility to improve it.
So here's my idea:
Move the stock air intake hose (the flexible one) from the hole in the fender to directly below where it attaches to the airbox.
I ran it down the fender well as to get the warmer air coming off the exhaust manifold.
I realize that warmer air is worse for performance but it's better for MPG. The colder, denser air
requires more fuel to atomize correctly at 14.7:1....conversely, warmer air is thinner and requires
less fuel to reach the stoichiometric goal. The trade off is that the less fuel, the worse performance....but it's an HHR.
Like I was telling my wife, my HHR is my mileage hot rod. I want my go-fast cars to go as fast as possible....
I want my HHR to get the best mileage possible.
I won't get to test it out until Monday, but what are y'alls thoughts?

Here's where the stock intake hose went:
Attachment 23113

Here's where I moved it to:
Attachment 23114
Attachment 23115
Attachment 23116

The intake air temp is measured by the MAF, the MAF plays a big role in A/F ratio. Mine usually reads about 20 degrees higher than the ambient temp. The ambient air temp sensor is in front of the radiator (exact location depends on year).

Just general comments.

Cooler air intake temps usually increase the efficency of the motor. Are you running your heater at night while not running it during the day? Also are you running it in either defrost or recirc modes? Both of those modes will turn on the compressor and rob your motor of power making it work harder to make the car go the same speed.

Trial and error! Let us know the results after Monday's run to work and back!

How are you getting the averages for just the one way trips ? If you're just resetting the MPG avg each way in the DIC, then I doubt it's going to be a very accurate number with such a short distance averaged.
If you're using the instant MPG in the DIC, then I'm sure it won't be very accurate.
The difference (if there really is one) could just be because of the day or night air quality, not temperature. Night air may be cooler but will most likely have a higher moisture content.

Since the accident, I haven't replaced the a/c condenser..I just removed it. So the compressor won't kick on. I didn't see a need to replace the condenser and get the A/C back up and running until the warmer temps.
I always reset my avg mpg during every fillup. On the way to work the average goes up, though not as dramatically as I go through the tank. On the way home from work though, the average goes down. I habitually toggle between the avg and instant mpg's. As I near the end of the tank, I usually leave it at instant mpg's because it won't make much difference to the average at that point. I've got a pretty good beat on how the vehicle drives and it's sweet spot. I'm just trying to extend that sweet spot, lol.
I realize the colder air is denser and it's more difficult to push the car through the denser air at nights. I can't do anything about that, other than some aerodynamic mods.
I have a 20 mile commute to work, with about 15 of that being highway miles (average between 60-70mph). I rarely hit traffic with my commute because I go to work at 1pm and come home at 10pm.
I'm anxious to see what, if any, difference this will make.

The AVG MPG calculation is more complicated than most people think. Just resetting it does not always "reset" it, if you remove the gas cap then reset it you get a better real idea. That's part of how the computer knows there is a fuel fill event.

And then it takes into account the Mass Air Flow and the injector pulse width and other things I'm sure.

In the days or yore when everyone had a carburetor on their car a lot of the air cleaners had some kind of chimney that went between the exhaust manifold to the snout on the air cleaner.

Most folks would somehow manage to mangle the tubing to the point that it no longer functioned. Replacement was usually fairly costly so they just ran their car without it.

Through the cold weather it really did make some difference in your over all MPG but gas was pretty cheap back then so most folks simply didn't care.

My first car was a 1960 Pontiac Catalina with the 389 and a three speed automatic. It had originally had a pleated aluminum chimney between the exhaust manifold and the air cleaner snout but it was totally gone when I got the car.

I put a piece of rubber hose in its place. That 'worked' but it didn't take long for the rubber to get hot enough on the manifold end to darken, get hard, and crack. I experimented a lot and came up with a pleated length of steel tubing to put between the manifold and the air cleaner snout.

I have no clue what the pleated steel tubing had come from, I think it may have been on a large air compressor, I was just happy to find it.

Although I never did get to legally drive that car, dad did sometimes and having that tubing in place really did make a difference.

I have often wondered why they deleted having such a thing on these newer cars.

I remember that tube and you are right most of the time it was just gone. I don't even remember for sure what it was called but I think it was called a "heat shroud". It warmed the air going into the breather.

How can that be? There's no sensor at the fill cap. Unless the computer sees the evap pressure suddenly go down from the pressure sensor on top of the tank....but the car is usually off when people fill up so the pcm isn't even powered up.
Although I suppose when the car gets restarted, the pcm will see that the evap pressure is at zero. Seems it would simply be easier to use the signal from the fuel level gauge to signal a fuel fill event, lol.