2016 Cruze 1.4 LT horrible on gas

If the turbos boosting at all it kills mileage 1.4 tiny engine needs a turbo to move the vehicle. Still it should hit 30 mpg have the dealer check it (fuel trim ST & LT real time) out make sure all controls were plugged in when it was built. No modern vehicles Don't need break in time.

There is going to be a break in period. Be patient.

Okay it just worries me, first brand new car. How long would you say the break in period last?

I have never had a vehicle get noticeably better mileage after the break-in period, never. This includes probably 2 dozen new vehicles over many years. Take it back to the dealer cause it sounds like something is wrong with it and it is still under warranty.

My 2011 Cruze 1.4 auto never get's past 30 mpg even all highway. Just the nature of the beast. Heavy car small turbo engine. Do any city at all MPG will crash because turbo kicks in a lot with stop and go. Make sure plug gaps correct, some claim GM is pretty flaky about all plugs having same gaps. Tire pressure needs to be above GM recommended. 30 psi for ride and comfort, Eco models runs at 36 or better. Probably where all Cruze should run or close. Still, all small turbos have the same disappointing MPG's with a heavier vehicle. They just work too hard to save fuel. Unless you drive like granny, you'll never see MPG ratings.

My 2012 cruze with the 1.4 gets between 42 amd 48mpg highway...

The cruze and other small engines get poorer mileage in winter cold than summer heat. Still with my cruze I get about 24 miles per gallon in the winter and 32 miles per gallon approximately in the summer.