MPG decline when off or in idle

Not sure about it moving overnight. If you have recently reset (manually or by filling up) the MPGs will move around very easily. When the car is warming up but not moving, the ICE is burning gas but no distance is being covered so you're getting 0mpg. That will be pretty detrimental to your average MPGs. The same thing happens when I leave the wife and kid in the car with the AC on, each time the battery gets low the ICE kicks on to recharge. Its pretty surprising how quick that can ruin your average MPG. In general its better to just shut the car off, or open all the windows and turn all the accessories off when just sitting with the car on to minimize this when possible/convenient. As far as the warmup cycle goes you are better off just waiting to start until you are ready to go. If the ICE is going to run anyway, you might as well be moving. I believe you will also get through the warmup cycle faster and improve your overall MPGs if the ICE has some load on it, rather than just idling.

Rob

 

Yes: idling wastes gas. Don't do it. The fastest way to warm up a Prius is the same as any other car. Drive it, gently for the first minute or two.

 

Also, if you leave your climate control on, it will keep the engine running to help warm up the inside of your car. Whereas normally, after warm up, the engine will turn off at stop signs/lights, if you have your climate control on, the engine will keep running at stop lights/signs.

Unless it is really cold in my car, I always keep the climate control off until I get on the highway.

 

In the case of the NHW11, I like to use a 25 mph average speed for the first 1.5 miles at temperatures of 60F or warmer. As often as possible, I slip into "N" for the glide since this further reduces fuel consumption even when waiting at a light or stop sign. But after 1.5 miles, you'll be in S3 and if you can come to a stop and let the ICE autostop, you'll be in S4 and full hybrid mode.

Bob Wilson