I wouldn't read too much into that, my engine always starts as I back out of the garage, but the car has been very consistently providing 40 mpg, day in and day out. Be aware that being in electric mode is not the key to good mileage. The key is the regen mode while braking, and the computer babying the IC engine, with acceleration and hill climbing support from the electric motors, and then storing electricity at every opportunity while the ICE is in an efficient low speed, loaded, mode. Keeping the engine loaded, with the throttle plate open makes the engine a lot like a diesel, no wasted energy just creating a vacuum in the manifold. Of course there is much more to it than that regarding the efficiency of the system, but it is one of the best systems out there. Others on this forum have much more expertise than I do on the subject. The engine sometimes will start just to warm itself up, or for some other not clear to us reason. I wouldn't try to second guess the computer.
See my full mpg chart, every gas event has been logged for 76,000 miles. The computer summaries, when you zero it at fillup, are usually very close to actual measured mpg.
Edited by VonoreTn, 17 September 2013 - 10:40 AM.