No problems.
This is a a great motor car, very reliable. Fuel economy averages around 31mpg, or around 9.75 liters per hundred Km. I have serviced it myself from new and used only genuine parts, filters, belts and coolant. I have replaced the tires at 70,000kms and the battery at approximately 75,000kms. It will require front disc pads at the 100,000km service. It will easily and consistently get 720kms before refilling the fuel tank.
The only minor concern is the the low fuel warning light only comes on when there is around 6 litres of fuel remaining as I live in a rural area and fuel stations are more remote, therefore I fill the tank by the odometer so I do not get caught out.
Also I am 6 ft tall and find that the seat height has my head near the roof and I am looking through the top section of the windscreen.
Resale value is artificially low because the new Carnivals are getting cheaper all the time.
Dealers are not interested in support for the owner mechanics and it took quite a bit of arm twisting including writing to KIA head-office to be able to purchase a repair manual.
The interior is very handsome in tan leather and everybody that has traveled in the Carnival love the overall ride comfort and spaciousness of the car.
I have been using a Kia Carnival for some time now and find that the fuel consumption you mention cannot be experienced.