My new 2006 PT Cruiser Touring Edition with the regular non turbo 2.5l engine was giving me about 23 mpg highway after about 500 miles of use. I also wasn't sure if the automatic transmission was shifting properly. I disconnected the battery for 30 minutes to reset the transmission shift pattern. During that time I drained out the factory loaded motor oil and refilled with 5w-30 Mobil 1 synthetic. I reconnected the battery and took it for a run thru small city traffic, then took it out on the interstate for a 25 mile cruise at 65 mph. So far I am seeing about a 2 mpg increase. Steve