So I now have 250 miles on my new 2014 c4s.

Today the light came on telling me I needed gas. Claimed to have less than 50 miles before empty. So I went and filled up. I only took 13 gallons to fill. Unless I am reading the specs wrong, the car has 18 gallons. Doesn't seem like a very accurate reading of the gas unless I am looking at this all wrong. Has this happened to anyone else?

 

It is quite possible the nozzle cut off prematurely due to foaming (depending on how quickly the gas was flowing).
These gas tanks are notorious for foaming up, causing the cut-off to occur.
What I usually do is turn the nozzle upside down and that helps with the foaming issue.

 

After you filled up, did the gauge show full and how many miles did it show until empty. If your gas gauge showed full, then this could be a issue, if not then you foamed it and did not top it off.

 

The car will tell you the remaining distance based upon the previous average mileage.

Example, I get 9mpg at the track and get a low fuel warning right below 1/2 tank because it thinks I will run out in 56 miles roughly. When I leave the track, the remaining mileage goes up as I drive on the expressway.

Watch the gauge, not the remaining mileage for best results.

 

I turn the nozzle 90 degrees clockwise and it fills full every time

 

What J08080808080 said. Your average MPG is all screwed-up because they probably let the car idle a bunch while doing the PPI and delivery and showing you how to synch your phone. Reset the trip information in the PCM and it should do better next time.

Unless the gas gauge was showing below 1/4 tank... if that was the case, and if it also showed full after you filled-up, then your gauge needs calibrating.

 

thanks all. it did show full after the fill. I am tracking this next tank to see what happens. it was not a foam issue from what I gather...

 

J080808, I have a similar experience and find it annoying. Right about 3/8ths of a tank, I get the low fuel light on the track, and run it down to about a 1/4 or so before filling. I usually use about 1/2 a tank every 30 minutes of track time.

Yesterday, on the way home from a track day, the light did go off as the mileage climbed when on the highway. I get about the same mileage as you 8-10 mpg depending on the track.