rob_engineer

If this helps, here is what my mileage looks like in the first 20,000 miles on my 2012 JKU with manual trans and 3.73 rear. I did see about 0.5mpg drop with cold temperatures and winter gas. I now have 26,000 miles and will be updating the chart soon. Below 15.5 is towing. Above 19.5 is 100% highway.

napamat87

Mine runs great , I had an awesome dealer do my head swap here near Houston where I.live....I.had no tick, no cel , nothing . They just agreed to fix it . I get 22 on the highway and 18 in town ....I love my powerhouse pentastar! ...

Grand Umpah

In the absence of throwing a code, I doubt that you'll get any action from the dealer.
I have a '12 JKUR manufactured in Aug. '11, and in July of 2012 it threw a code. Dealer flashed it, and it was only about 30 min. later that it threw the code again.
I went to a second dealer, and they didn't mess around; they did a "leak down" test and that confirmed the head/valve problem; that's the test that has to be performed.

But to answer your question about mileage, I got the results of the leak down test a couple of days before I was scheduled to take a road trip to Montana. The dealer said "no problem; drive the Jeep." I did, and I don't think that my mileage was any different compared to the months prior (and I put 3300 miles on during that trip).
I'm not saying that the head problem can't affect mileage, but I don't think you should try to equate your mileage to a mechanical defect.

Again, I believe that there is only one way to absolutely diagnose the problem. If you wanted to take the chance and pay for the leak down test and it was positive, perhaps you'd have some recourse. Otherwise, wait for the code to throw.