(Maybe this topic has been addressed elsewhere on the forums. If yes, please send me the link and I will check the conversation there.) When the EV mode is exhausted (battery at 0%, or sometimes at 2-3%), the Prime will initiate a warm-up cycle to move into HV mode. Modern cars, and the Prius in particular, can warm-up pretty fast, usually in 1-2 mins (depending on external temps, of course). My previous Gen4 would shut the ICE off after initial warm-up sometimes in less than 1 min. But in the back of my head I am always thinking of the moniker "don't drive fast on a car that is not properly warmed up or you will end up 'destroying' the engine." The Prime seems instead to not care at all about what happens after warm up. It will use the ICE in EV Auto when accelerating fast, without any noticeable warm up before-hand, or when EV mode is finished at highway speeds, it warms it up for x seconds, and then merrily goes on pushing the car at those same high speeds, theoretically destroying itself. In other words, how good of a warm up is the one performed by the Prime when switching (on its own) from EV to HV at highway speeds? How much "damage" does the ICE does to itself, when it is summoned out of the blue in EV Auto mode? How much warm-up does the ICE really need, since it seems that the Prime itself doesn't really care too much about it being properly "warm" before regular use?
The ICE may be running but it’s power output is reduced until it’s safe to do so. I believe @John1701a has several videos on this.
This topic gas been beaten to death over the years. I have created quite a number of videos documenting the warm-up process. Here's one of the newer examples with commentary to highlight detail shown on the aftermarket display.
