My 2011 Boxster 2.9 has been on a downward fuel economy trend for nearly 2 years now. It is especially noticeable at lower speeds during stop and go driving in rush hour traffic. My commute has remained the same for more than 10 years. I have questioned the dealer about this during service visits and have been told that is due to California's special fuel blends. I question this response as my previous Boxster, a 2008, actually experienced improved fuel economy as the miles were added. My 2011 is approaching 120,000 miles. Any ideas as what may be causing the reduced fuel economy.
Usualy culprits are... spark plugs, oxygen sensors, air filter, MAF sensor... how bad is your mpg? I feel like the 2.9 engine have been on the thirsty side esp when running on the higher rpms. I have been seeing an average of 14-17 mpg, with a fairly aggressive driving style.
Hey, you have 120K miles on the car, what would you expect? lol You say your commute has remained the same for 10 years. I noticed that my commute "the route" has stayed the same but the amount of traffic has increased significantly in LA over the last 10 years. So there is a lot more stop and go and waiting now then there was 10 years ago. You did not say what your milage was or is? I had an 07 CS and was lucky to get 15 mpg, 13 to 14 was not unusual. Anyway, you might try a bottle of injector cleaner, it couldn't hurt. Good Luck.
Also keep in mind that ethanol in your gas will reduce mileage.
-- copy that; '06 CayS, 75k mi, 11 mi stop & go commute = 14-16 mpg...
Amount of decrease in fuel economy. From the time I purchased the Boxster in 2014 at 14,600 miles until 10/14/2018 at 99,600 miles my overall average fuel economy was 22.6 mpg. Since that time my average fuel economy has fallen to 22.0 mpg for the last year or 19,500 miles. My overall fuel economy peaked at 22.8 mph in June of 2016. My current overall fuel economy is 22.5 mpg. With my previous Boxster, a 2008, my experience was the opposite. The fuel economy was increasing as more miles were added. It averaged 25.5 mpg during the 85,000 miles that I added during my ownership.
- To note: The mileage you’re citing is ‘average’ and dependent upon stop n go vs freeway miles. Mileage I noted above for ‘06 Cay S is soley based on stop n go commute miles...
