First of all, and most important, is that if you are getting 9 - 11.5 L/100km, that is 26.3 - 20.5 US mpg, which sucks, and I understand why you are disappointed. The 2009 1.8L auto is rated at 31 US mpg highway, which is 7.6 L/100km.The 60% is wrong, you are using the 37 mpg imperial, and comparing it to 20.5 mpg US. If you use the correct highway rating of 31 mpg US, then you are only getting 66% of the rated mileage, or 34% less. If you use L/100km, then 11.5 is 51% above the rated 7.6, which sounds worse, but it's the same. Either way, I'd be very disappointed only getting those numbers, but calling it 60% is wrong.As several have mentioned, running at those speeds is not in the efficent range for these cars. Wind resistance is the main factor. My worst gas mileage was on really long highway trips, where the speed limit was way up there, at or above the speeds you routinely drive. Most of the time I'm on well policed 55 mph (~90 kph) roads and my efficiency is way up on those slower roads.Allowing the car to warm up for five minutes will result in being able to drive a warm car, but it costs five minutes no kilometer idling, and will bring down the efficiency. Some argue that the long term life of the engine is increased by not loading the engine while cold. I turn mine on and go, but it almost never gets as cold here in Maryland as it can in Ontario, and I have a garage, which means no ice scraping Still that warm up does use fuel to not move the car. It's more of a factor if you warm the car up for five minutes to drive for ten that it would be to warm the car up for five minutes to drive for an hour. Also, running the defroster will cause the AC compressor to be cylced on and off, that saps power some, so try to use the defrost or defrost/floor settings only when you really need them.Around here, they use a different formula gas in the winter, I forget why, maybe a pollution control thing, but it does adversely affect efficiency. Some of the gas stations here use a blend that contains more ethanol that the gasoline sold at other stations, the higher the ethanol content, the lower the efficiency.There are a number of possible causes for poor fuel efficiency. The most common cause for poor fuel efficiency is driver habits, and from what you've said, I only see the driving at avg 118 kph. That may be a totally reasonable speed for the roads and traffic, but it will hurt your efficiency. A number of factors also come into play with it being winter, and if you decide to keep the car, you should see an increase in warmer weather.
viewtopic.php?f=17&t=6088&#p65128 has an excerpt from the 2003 service manual listing possible causes for fuel efficiency being less than expected, There are many possible causes that would take a lot ot fime to check, and there are several that are not repair items, and it is very difficult to rule them out.I have very limited dealer service experience, and would not expect them to invest days quantifying your car's performance. The last new car I bought was this Vibe, six years ago tomorrow. However, it sounds like this Vibe is your sixth new car in five years, so you have a lot more experience interacting with dealerships than I hope to ever have. While I would not expect the dealership to spend a lot of time trying to diagnose your car that may or may not have a repairable problem, it does seem that the quality of treatment did not meet the standard which you feel you should be treated. Perhaps they should have explained it better. Perhaps the Audi, VW, Honda, Toyota and Nissan dealerships would have given you a loaner car while they spent days performing detailed analysis of your vehicles for free, and if they would, then certainly nobody can fault you for giving them repeat business. For me, it seems unreasonable to expect them to do that, so I wouldn't rule out American cars because of that, but as I said, I have a lot less dealer experience than you.