Need a math Guru to figure this out

I am lousy at percentages, so hopefully someone here can considering there are some rally bright people on this forum.

2010 FFH, rated 36 Highway, 41 City 39 Combined

Cold weather driving, seeing about 36 MPG over a 23 mile 90-10 highway/city with 55 MPH limit.

2013 FFH rated 47/47/47

Cold weather driving, seeing about 34 MPG same exact trip, driven exactly the same.

Temp is at 23 * F.

What are the percentages for subtraction of cold weather, and mathematically what should be the expected MPG for each car?

 

Theoretically speaking.

Just trying to determine if what I am seeing in loss on the new car is feasible. If you look at what I get in warmer weather in the 2010, which is 39, and in 23* weather it drops to 36, whats that percentage. Should I not see a similar percentage drop on the 2013?

I also dont give a hoot that its not an EPA test, its a real world test between similar cars on the same roads, same temps, same exact driving conditions to compare each car to the other.

So in Theory I should expect to see a higher MPG reading on the 2013 that is rated at 47 combined than the 2010 that is rated 39 combined, should I not?

Isnt there some calculation regarding temp drop vs ICE MPG?

 

Of all the hybrids I have driven, this new one is the only one that does get anywhere near the rated numbers no matter what I do. Yeah I know its an estimate, but still out of the other 3 I had, the Prius, the TCH, I was always near them no matter what the temps were. All I'm looking for is a gradient of what to expect. Someone on another forum said up to 17 MPG drop in the cold. That seems pretty far excessive, especially since I have never seen that much of a drop on any of the other cars. The Prius had the largest drop, of 15, but it was also -10* F that day.

I need to gather up as much information as I can to present to my dealer that there is something not right with this car, considering it gets no where near what I am getting in my 3 Year old car, and I doubt I will gain that much MPG once it breaks in.

 

I wish I could but they are hard to find. One of the other people I know who had a 2012 and was averaging 43 MPG got a new 2013 and from what I heard is not doing too well either, but that was through the dealer, so without talking to him direct, I cant say for sure.

However I did test drive a Cmax and did better in that one than I did in the Fusion when I test drove it. Should have been a sign. On the short test drive it got 38 MPG. My Father in Law has a Cmax too, and is getting 43 in it.