FYI .. This morning I was playing around with my 2010 Prius "B" mode - I realize today that when the Prius CVT is in "B" mode the Prius ICE won't turn off even when it is at a complete stop -- instead the ICE runs/idles at a 996 RPM / .20-.40 GPH while stopped in traffic. The coolant temperature (@190F ) doesn't matter, Battery State of Charge (54% soc) doesnt matter. To re-enable the stop-start idle technology - I had to switch the Prius CVT back to "D" mode. I end up burning a bit more fuel on this trip because it took me a while to realize that I was in "B" mode and that the stop start idle technology had disabled in the "B" mode ...
I'm pretty sure I've seen the engine off in B mode, but you are absolutely right - it is very reluctant to do so. B mode is not useful if your primary objective is to save gas. It's more useful for ease of driving down a steep slope, or saving wear on your brakes.
Interesting. I didn't know that. I'll have to give it a whirl on my 06. That might be another reason some people get "poor" mileage when driving in B mode.
I was playing around with - practicing running in B mode while going down some steep slope in my commute- the Prius more aggressive goes into automatic regenerative braking mode and seems to recharge the battery faster in B mode when I do this ( or atleast it feels that way). I had forgotten to switch back to D mode after the downhill segment and saw my MPG drop from my normal numbers - it took me a while to figure out what was going on. At first I thought it had something to do with the ECO, PWR button setting - then I realize I was in B mode and I switch back to the D mode and all was back to normal.
