ICE on off on off on off on off

Yup, if you take a look at your energy screen it usually occurs when there is a high (green level) State of Charge on the battery. The car is bleeding off some of the charge as part of it's battery maintainence programming. It'll also, sometimes, do that when the ICE temp is at an in between point...IOW, it must be at a certain temp (let's just say 140 degrees) before it'll shut off on it's own at a stop. So if, when you stop, the ICE temp was 141 degrees the ICE shuts down....sit for just a few seconds and it cools down to 139 and it starts again, almost immediately the temp goes back over the 140 threshold and shuts off again...cycle repeats.

But honestly, the most common reason is the first one I mentioned.

 

IM, Where are you?
It was -2F this morning in Northern Chicagoland as I drove to work. My ICE was on more on than off. Even at a dead stop. And by the time it was warm enough to shut off, it was time to move and it came on again.

 

Yeah, my battery has reached and maintained levels of green I NEVER see in the summer when I can stealth with ease. I would love to sit in traffic and crawl at sub-25 speeds to bleed off the charge and save a little gas.

 

Let me add something here to put things in some perspective. John has about 5-6 years of experience driving the Prius. His technique is optimal. And I think that is a large part of the reason he so rarely sees all green, even in winter.

The battery SOC is maintained at a much higher level during the winter cold than in the summer heat...if left to its own devices. I am entering my 3rd winter with the Prius so my first winter is still pretty clear in my mind. I vividly remember several stops on my regular commute where I would routinely encounter the on-off-on-off cycling with a nearly full SOC of the battery. And these were rolling tiny hills, not big long mountains that this occured on. But at that time I was doing absolutely nothing at all special with my driving...didn't know what to do. Thus, the conditions were such that with the cold weather higher permitted SOC plus road conditions that allowed that SOC to climb just a bit more than usual as I rolled to a long stop I'd get in that condition.

Now a days, however, that doesn't happen. The only time I've encountered any of the on-off cycling is on a few long hills that I drive once or twice a month IF I have to stop at a light near the bottom of the hill...I'm peaked out at 8 bars and it'll cycle unless I managed to hit the EV button before coming to a full stop. (which, btw, I do there b/c the next part of the drive is a slightly uphill 30mph 1/2 jaunt so I can usually do the whole thing on just electric with that full charge). Those areas where I used to experience the cycling I no longer do. I attribute that due to some changes in my driving technique...namely much more gliding..such that my overall SOC, even in winter, rarely goes over 6 bars since I encourage stealth and gliding when possible/benefitial.

And, to answer the question about using the EVb--yes, I think it does help and, indeed, at one part of my commute in particular it's slightly uphill as you approach the light for about 200 meters. If I don't use the EVb the ICE will run but with in the 70mpg range spilling excess power into the battery--that's what used to top off my charge at that particular stop and cause the cycling. So, now, I hit the EV button as soon as I drop to 33mph and use a little battery charge to maintain enough speed to coast calmly to a stop.