Video - I have a 2011 CX-7 with 166k miles on it. I bought it a few months ago and always averaged 24.7mpg mixed no matter what. I've changed the oil twice since I bought it at 5k miles each time. I always make sure it is the 0w-30 manufacturer recommended. Over the last month or so, I have seen a significant drop in my fuel mileage. I have reset the computer a number of times, both during Highway, city, and mixed trips. It always used to jump around for a few days before settling into an avg. of 24.7 mpg. I also replaced the air filter. Each time I reset it now and drive for a few days, it will start at 23 or so and drop over the next couple of days of driving. It seems to be decreasing steadily every 1.5 or so weeks. I am now averaging 20-21mpg mostly highway.

I've also been noticing a random rattling coming from the front right side of the engine. This did not affect the fuel mileage and has been going on for some time, but I'm starting to wonder if this could be the cause as well.

My first instinct was to blame a faulty timing chain tensioner, but the dealership told me that this problem was highly unlikely to arise in the 2.5 and was usually isolated to the turbo engines. It does not make the noise all the time. It is at random hot or cold and occurs at long and short intervals at complete random with or without the AC on.