Check your spark plug gapping. Also pre-warming the car will really only waste gas. After about 3 minutes in the winter, it reaches 120F (49C) and doesn't change much more than that. The tiny engine doesn't generate much heat without a load on the engine, unless you have ice to scrape off, just drive it right away don't waste the fuel trying to warm it up. It'll take hours to get up to the 226F (108C) operating temp. When the car is running but not moving you're getting 0 MPG. That will definitely cause a massive drop in economy. I've been averaging 27-31 MPG (8.7L/100km - 7.6L/100km) in the winter with moderate stop and go mixed with 40-60 mph (64 kmh - 96kmh) back roads. In the summer I get between 34-39 MPG (6.9/100km - 6.0L/100km). Also note the combined fuel rating. Never assume you'll AVERAGE the MAX highway number. You simply won't unless you fill up your already warm car, and hop on the highway doing 55 mph (88 kmh) for the entire tank of fuel. For instance my car says it will get 30 MPG (7.8L/100km) Combined which is a much more realistic estimation. And I've averaged 7.0L/100km over 20,000 miles (32,186 km) So I'm doing better than the rated fuel number for my car. (1.4L turbo) The NA 1.8L of course won't be quite as efficient. I do think 12l/100km is sort of inefficient but not unrealistic. But you shouldn't be averaging that on every tank of fuel.Thank you for your reply.
Outside temperatures here in winter has been usually between -15 and +5 deg C, and I know that it affects to fuel consumption. Terrain is flat and I'm not driving with heavy foot. While driving in warm weather the fuel consumption does not drop significantly. I live in cold climate country so I know how the weather affects to fuel consumption. So the cold weather does not alone explain the high fuel consumption. In addition in here its normal that people pre-warms their cars engines before driving in winter.
But maybe you are right, the car just consumes a lot of fuel. Compared to my previous cars, Cruze consumes much more fuel than the manufacturer says. So that's why I'm disappointed and I tought there might be some sort of typical problems in Cruze which affects to fuel consumption.
Have a nice day