Took me 17,000 miles to work this out....

Just remember Ben, the engine will come on if the ECU needs to heat the coolant system or supply optimum power for any of the systems. There is a logic in there, it's not always easy to understand it though.

 

I wouldn't count on it always happening that way - if you start going down a gentle incline after driving on the level with ICE running, but with a little accelerator to hold your speed, generally the ICE will turn off and use just battery, unless the battery hasn't got sufficient charge or it needs to heat the car. Or any of many other reasons why it decides to "do it's thing. Sometimes I've encountered what you said - and I can't fathom why.

The same as tonight, full battery, hot night so no heater, a/c, been driving about 25km, last 2 km at 70km/hr. Stop at traffic light, pressed EV because there was another light 100metres up the road, and got "EV UNAVAILABLE" with no reason given.

It's a mystery sometimes.

 

I can only say one thing: just drive it.
Reduce sudden and strong accelerations and braking. Predict traffic. Drive "smooth" whenever possible, reasonable and safe. Keep up with traffic. You will have the best fuel consumption.
This is my second Prius in since 2009, whenever I tried to do anything else and not drive smooth as a result because too worried of how I would accelerate, etc, I had lower MPGs. I drive it smoothly, I get the highest MPGs. I also think that P&G is not necessary anymore with Gen4 to get great MPGs. What gets great MPG is smooth driving, well inflated tires, and lower speed if possible/reasonable.
Also consider that temperature affects the MPGs, and if the heater is on, the engine will come on to keep warm, or it will stay off because more efficient in that particular situation. Let the engine decide. Toyota has almost 20 years experience in this. Let the computer decide what to do with its hardware.
Sit back and enjoy the drive, don't think about it.

PS: the "score" is weird - when it is low, sometimes I get great MPG - when high, I get the opposite in the same or similar conditions - I simply don't look at it anymore....

 

The Prius tends to keep the petrol motor running at its most efficient, draining & recharging the battery is generally more efficient, especially when regenerative braking is used on downhill portions of the trip.

 

It has the mind of a woman with a headache.
I'm waiting for mine to give me the message, "Score: 1, surrender your driving licence to the nearest police station"

 

Just drive the car. if your light on the accel your mileage will be fine. I never reset the mpg display an it's at 61.2

 

Thanks for that. I believe I have seen that happening once or twice now and thought it was a glitch/lag in the display diagram.

 

I have found in my gen 3 that this technique (which I also use at times) is easier in PWR mode. The car seems to be reluctant to turn the engine off in PWR mode if your foot is still on the gas unless the battery state of charge is very high. I drive almost exclusively in PWR mode and you mentioned you have started doing that as well - my theory is that the car wants to remain as responsive as possible in power mode, thus keeping the engine on to avoid the small delay of tuning it back on if it thinks you might want to start it again soon anyways.

It might be possible to get the same behavior in the other modes, but you'd probably have to press the pedal further down.

I usually use this technique when I am traveling around the speed where the engine can't shut off and know I have a long shorter stretch coming to conserve battery power.

 

That does not look like Gen 4. At least. Or mine. The OP has a Gen 4. Our HSI looks different.

 

I thought perhaps you lost your way and thought you were in a Gen 3 thread.
Perhaps if you talk nicely, she will let you drive the Gen 4 more?