This page contains an almost complete history of my car's fuel economy. Data from October 2005 to February 2008 was lost a number of years ago, and the information from that period has been extrapolated as one large entry from all of the data gathered after that period. You may also notice that my 318iS' fuel economy shows an overall decrease after late 2008. At that time I moved to a different location, closer to my office. That enabled me to ride my bike to work almost every day. Because of this, the times that I drove the car were usually for very short distances and errands, so fuel economy suffered overall. Prior to my move, I would drive ~45 miles on the highway daily. Another factor in my decreased mileage was a wiring "oops" when I first bought the car, and the wide-band O2 sensor system I had installed. In short, the fuel injection electronics were only getting about 7V instead ov 12V thanks to a sloppy wiring repair. The wide-band O2 sensor system was also improperly grounded, which caused the ECU to run things pretty rich. Thankfully, all of that was sorted out around May of 2011.

The original engine died at around 220,000 miles from a broken timing case. It was replaced with a 2.1L, professionally built M42 from Metric Mechanic. It is still too early to really say what the impact on mileage will be, but so far it looks a little lower. This is probably largely due to me driving the car a bit harder than I used to since the extra 70BHP is a lot of fun! The increased displacement probably also causes a hit to the mileage.

The car used to attain 30-32 MPG when the original engine had under 200,000 miles on it (closer to 27MPG now with my new, larger displacement engine) on long highway drives if I kept the speed under 75mph, but road trips are typically done in my fiancee's Honda Civic since it can easily get 38-44 MPG on the highway. If I drive tamely around town running errands and such, the car usually gets 25-27 MPG. The two plots below give a graphical depiction of the car's fuel economy over the years, and the price of gasoline in the San Francisco Bay area of California.

All fill-ups used 91 octane "premium" gasoline.